Table of contents

By performing two-dimensional special relativistic (SR) magnetohydrodynamic simulations, we study possible signatures of gravitational waves (GWs) in the context of the collapsar model for long-duration gamma-ray bursts. In our SR simulations, the central black hole is treated as an absorbing boundary. By doing so, we focus on the GWs generated by asphericities in neutrino emission and matter motions in the vicinity of the hyperaccreting disks. We compute nine models by adding initial angular momenta and magnetic fields parametrically to a precollapse core of a 35 M_☉ progenitor star. As for the microphysics, a realistic equation of state is employed and the neutrino cooling is taken into account via a multi-flavor neutrino leakage scheme. To accurately estimate GWs produced by anisotropic neutrino emission, we perform a ray-tracing analysis in general relativity by a post-processing procedure. By employing a stress formula that includes contributions from both magnetic fields and SR corrections, we also study the effects of magnetic fields on the gravitational waveforms. We find that the GW amplitudes from anisotropic neutrino emission show a monotonic increase with time, whose amplitudes are much larger than those from matter motions of the accreting material. We show that the increasing trend of the neutrino GWs stems from the excess of neutrino emission in the direction near parallel to the spin axis illuminated from the hyperaccreting disks. We point out that a recently proposed future space-based interferometer like Fabry–Perot-type DECIGO would permit the detection of these GW signals within ≈100 Mpc.

The objective of this paper is to determine the level of obscured star formation activity and dust attenuation in a sample of gamma-ray burst (GRB) hosts, and to test the hypothesis that GRB hosts have properties consistent with those of the general star-forming galaxy populations. We present a radio continuum survey of all z < 1 GRB hosts in The Optically Unbiased GRB Host (TOUGH) sample supplemented with radio data for all (mostly pre-Swift) GRB-SN hosts discovered before 2006 October. We present new radio data for 22 objects and have obtained a detection for three of them (GRB 980425, 021211, 031203; none in the TOUGH sample), increasing the number of radio-detected GRB hosts from two to five. The star formation rate (SFR) for the GRB 021211 host of ∼825 M_☉ yr⁻¹, the highest ever reported for a GRB host, places it in the category of ultraluminous infrared galaxies. We found that at least ∼63% of GRB hosts have SFR < 100 M_☉ yr⁻¹ and at most ∼8% can have SFR > 500 M_☉ yr⁻¹. For the undetected hosts the mean radio flux (<35 μJy 3σ) corresponds to an average SFR < 15 M_☉ yr⁻¹. Moreover, ≳ 88% of the z ≲ 1 GRB hosts have ultraviolet dust attenuation A_UV < 6.7 mag (visual attenuation A_V < 3 mag). Hence, we did not find evidence for large dust obscuration in a majority of GRB hosts. Finally, we found that the distributions of SFRs and A_UV of GRB hosts are consistent with those of Lyman break galaxies, Hα emitters at similar redshifts, and of galaxies from cosmological simulations. The similarity of the GRB population with other star-forming galaxies is consistent with the hypothesis that GRBs, a least at z ≲ 1, trace a large fraction of all star formation, and are therefore less biased indicators than once thought.

Magnetic loops are building blocks of the closed-field corona. While active region loops are readily seen in images taken at EUV and X-ray wavelengths, quiet-Sun (QS) loops are seldom identifiable and are therefore difficult to study on an individual basis. The first analysis of solar minimum (Carrington Rotation 2077) QS coronal loops utilizing a novel technique called the Michigan Loop Diagnostic Technique (MLDT) is presented. This technique combines Differential Emission Measure Tomography and a potential field source surface (PFSS) model, and consists of tracing PFSS field lines through the tomographic grid on which the local differential emission measure is determined. As a result, the electron temperature T_e and density N_e at each point along each individual field line can be obtained. Using data from STEREO/EUVI and SOHO/MDI, the MLDT identifies two types of QS loops in the corona: so-called up loops in which the temperature increases with height and so-called down loops in which the temperature decreases with height. Up loops are expected, however, down loops are a surprise, and furthermore, they are ubiquitous in the low-latitude corona. Up loops dominate the QS at higher latitudes. The MLDT allows independent determination of the empirical pressure and density scale heights, and the differences between the two remain to be explained. The down loops appear to be a newly discovered property of the solar minimum corona that may shed light on the physics of coronal heating. The results are shown to be robust to the calibration uncertainties of the EUVI instrument.

We report the first two-dimensional mapping of the stellar population and non-stellar continua within the inner 180 pc (radius) of NGC 1068 at a spatial resolution of 8 pc, using integral field spectroscopy in the near-infrared. We have applied the technique of spectral synthesis to data obtained with the instrument NIFS and the adaptive optics module ALTAIR at the Gemini North Telescope. Two episodes of recent star formation are found to dominate the stellar population contribution: the first occurred 300 Myr ago, extending over most of the nuclear region; the second occurred just 30 Myr ago, in a ring-like structure at ≈100 pc from the nucleus, where it is coincident with an expanding ring of H₂ emission. Inside the ring, where a decrease in the stellar velocity dispersion is observed, the stellar population is dominated by the 300 Myr age component. In the inner 35 pc, the oldest age component (age ⩾ 2 Gyr) dominates the mass, while the flux is dominated by blackbody components with temperatures in the range 700 K ⩽ T ⩽ 800 K which we attribute to the dusty torus. We also find some contribution from blackbody and power-law components beyond the nucleus which we attribute to dust emission and scattered light.

The analysis of relativistically broadened X-ray spectral features from the inner accretion disk provides a powerful tool for measuring the spin of supermassive black holes in active galactic nuclei (AGNs). However, AGN spectra are often complex and careful analysis employing appropriate and self-consistent models is required if one has to obtain robust results. In this paper, we revisit the deep 2009 July Suzaku observation of the Seyfert galaxy NGC 3783 in order to study in a rigorous manner the robustness of the inferred black hole spin parameter. Using Monte Carlo Markov chain techniques, we identify a (partial) modeling degeneracy between the iron abundance of the disk and the black hole spin parameter. We show that the data for NGC 3783 strongly require both supersolar iron abundance (Z_Fe = 2–4 Z_☉) and a rapidly spinning black hole (a > 0.89). We discuss various astrophysical considerations that can affect the measured abundance. We note that, while the abundance enhancement inferred in NGC 3783 is modest, the X-ray analysis of some other objects has found extreme iron abundances. We introduce the hypothesis that the radiative levitation of iron ions in the innermost regions of radiation-dominated AGN disks can enhance the photospheric abundance of iron. We show that radiative levitation is a plausible mechanism in the very inner regions of high accretion rate AGN disks.

We present chemical abundance measurements for 47 damped Lyα (DLA) systems, 30 at z > 4, observed with the Echellette Spectrograph and Imager and the High Resolution Echelle Spectrometer on the Keck telescopes. H i column densities of the DLAs are measured with Voigt profile fits to the Lyα profiles, and we find an increased number of false DLA identifications with Sloan Digital Sky Survey at z > 4 due to the increased density of the Lyα forest. Ionic column densities are determined using the apparent optical depth method, and we combine our new metallicity measurements with 195 from previous surveys to determine the evolution of the cosmic metallicity of neutral gas. We find the metallicity of DLAs decreases with increasing redshift, improving the significance of the trend and extending it to higher redshifts, with a linear fit of −0.22  ±  0.03 dex per unit redshift from z = 0.09–5.06. The metallicity "floor" of ≈1/600 solar continues out to z ∼ 5, despite our sensitivity for finding DLAs with much lower metallicities. However, this floor is not statistically different from a steep tail to the distribution. We also find that the intrinsic scatter of metallicity among DLAs of ∼0.5 dex continues out to z ∼ 5. In addition, the metallicity distribution and the α/Fe ratios of z > 2 DLAs are consistent with being drawn from the same parent population with those of halo stars. It is therefore possible that the halo stars in the Milky Way formed out of gas that commonly exhibits DLA absorption at z > 2.

We present new observations of the [Ne ii] emission from the ionized gas in Sgr A West with improved resolution and sensitivity. About half of the emission comes from gas with kinematics indicating it is orbiting in a plane tipped about 25° from the Galactic plane. This plane is consistent with that derived previously for the circumnuclear molecular disk and the northern arm and western arc ionized features. However, unlike most previous studies, we conclude that the ionized gas is not moving along the ionized features, but on more nearly circular paths. The observed speeds are close to, but probably somewhat less than expected for orbital motions in the potential of the central black hole and stars and have a small inward component. The spatial distribution of the emission is well fitted by a spiral pattern. We discuss possible physical explanations for the spatial distribution and kinematics of the ionized gas, and conclude that both may be best explained by a one-armed spiral density wave, which also accounts for both the observed low velocities and the inward velocity component. We suggest that a density wave may result from the precession of elliptical orbits in the potential of the black hole and stellar mass distribution.

Despite the astrophysical importance of binary star systems, detections are limited to those located in small ranges of separations, distances, and masses and thus it is necessary to use a variety of observational techniques for a complete view of stellar multiplicity across a broad range of physical parameters. In this paper, we report the detections and measurements of two binaries discovered from observations of microlensing events MOA-2011-BLG-090 and OGLE-2011-BLG-0417. Determinations of the binary masses are possible by simultaneously measuring the Einstein radius and the lens parallax. The measured masses of the binary components are 0.43 M_☉ and 0.39 M_☉ for MOA-2011-BLG-090 and 0.57 M_☉ and 0.17 M_☉ for OGLE-2011-BLG-0417 and thus both lens components of MOA-2011-BLG-090 and one component of OGLE-2011-BLG-0417 are M dwarfs, demonstrating the usefulness of microlensing in detecting binaries composed of low-mass components. From modeling of the light curves considering full Keplerian motion of the lens, we also measure the orbital parameters of the binaries. The blended light of OGLE-2011-BLG-0417 comes very likely from the lens itself, making it possible to check the microlensing orbital solution by follow-up radial-velocity observation. For both events, the caustic-crossing parts of the light curves, which are critical for determining the physical lens parameters, were resolved by high-cadence survey observations and thus it is expected that the number of microlensing binaries with measured physical parameters will increase in the future.

In this paper, we present the Clustering-Labels-Score Patterns Spotter (CLaSPS), a new methodology for the determination of correlations among astronomical observables in complex data sets, based on the application of distinct unsupervised clustering techniques. The novelty in CLaSPS is the criterion used for the selection of the optimal clusterings, based on a quantitative measure of the degree of correlation between the cluster memberships and the distribution of a set of observables, the labels, not employed for the clustering. CLaSPS has been primarily developed as a tool to tackle the challenging complexity of the multi-wavelength complex and massive astronomical data sets produced by the federation of the data from modern automated astronomical facilities. In this paper, we discuss the applications of CLaSPS to two simple astronomical data sets, both composed of extragalactic sources with photometric observations at different wavelengths from large area surveys. The first data set, CSC+, is composed of optical quasars spectroscopically selected in the Sloan Digital Sky Survey data, observed in the x-rays by Chandra and with multi-wavelength observations in the near-infrared, optical, and ultraviolet spectral intervals. One of the results of the application of CLaSPS to the CSC+ is the re-identification of a well-known correlation between the α_OX parameter and the near-ultraviolet color, in a subset of CSC+ sources with relatively small values of the near-ultraviolet colors. The other data set consists of a sample of blazars for which photometric observations in the optical, mid-, and near-infrared are available, complemented for a subset of the sources, by Fermi γ-ray data. The main results of the application of CLaSPS to such data sets have been the discovery of a strong correlation between the multi-wavelength color distribution of blazars and their optical spectral classification in BL Lac objects and flat-spectrum radio quasars, and a peculiar pattern followed by blazars in the WISE mid-infrared colors space. This pattern and its physical interpretation have been discussed in detail in other papers by one of the authors.

We explore the suggestions by Uzdensky and Cassak et al. that coronal loops heated by magnetic reconnection should self-organize to a state of marginal collisionality. We discuss their model of coronal loop dynamics with a one-dimensional hydrodynamic calculation. We assume that many current sheets are present, with a distribution of thicknesses, but that only current sheets thinner than the ion skin depth can rapidly reconnect. This assumption naturally causes a density-dependent heating rate which is actively regulated by the plasma. We report nine numerical simulation results of coronal loop hydrodynamics in which the absolute values of the heating rates are different but their density dependences are the same. We find two regimes of behavior, depending on the amplitude of the heating rate. In the case that the amplitude of heating is below a threshold value, the loop is in stable equilibrium. Typically, the upper and less dense part of a coronal loop is collisionlessly heated and conductively cooled. When the amplitude of heating is above the threshold, the conductive flux to the lower atmosphere required to balance collisionless heating drives an evaporative flow which quenches fast reconnection, ultimately cooling and draining the loop until the cycle begins again. The key elements of this cycle are gravity and the density dependence of the heating function. Some additional factors are present, including pressure-driven flows from the loop top, which carry a large enthalpy flux and play an important role in reducing the density. We find that on average the density of the system is close to the marginally collisionless value.

We report the discovery of a wide brown dwarf companion to the mildly metal-poor ([Fe/H] = −0.24), low Galactic latitude (b = 188) K4V star HIP 38939. The companion was discovered by its common proper motion with the primary and its red optical (Pan-STARRS1) and blue infrared (Two Micron All Sky Survey) colors. It has a projected separation of 1630 AU and a near-infrared spectral type of T4.5. As such it is one of only three known companions to a main-sequence star which have early/mid T spectral types of (the others being HN Peg B and ε Indi B). Using chromospheric activity we estimate an age for the primary of 900±¹⁹⁰⁰₆₀₀ Myr. This value is also in agreement with the age derived from the star's weak ROSAT detection. Comparison with evolutionary models for this age range indicates that HIP 38939B falls in the mass range 38 ± 20 M_Jup with an effective temperature range of 1090 ± 60 K. Fitting our spectrum with atmospheric models gives a best-fitting temperature of 1100 K. We include our object in an analysis of the population of benchmark T dwarfs and find that while older atmospheric models appeared to overpredict the temperature of the coolest objects compared to evolutionary models, more recent atmospheric models provide better agreement.

Many population synthesis and stellar evolution studies have addressed the evolution of close binary systems in which the primary is a compact remnant and the secondary is filling its Roche lobe, thus triggering mass transfer. Although tidal locking is expected in such systems, most studies have neglected the rotationally induced mixing that may occur. Here we study the possible effects of mixing in mass-losing stars for a range of secondary star masses and metallicities. We find that tidal locking can induce rotational mixing prior to contact and thus affect the evolution of the secondary star if the effects of the Spruit–Tayler dynamo are included both for angular momentum and chemical transport. Once contact is made, the effect of mass transfer tends to be more rapid than the evolutionary timescale, so the effects of mixing are no longer directly important, but the mass-transfer strips matter to inner layers that may have been affected by the mixing. These effects are enhanced for secondaries of 1–1.2 M_☉ and for lower metallicities. We discuss the possible implications for the paucity of carbon in the secondaries of the cataclysmic variable SS Cyg and the black hole candidate XTE J1118+480 and for the progenitor evolution of Type Ia supernovae. We also address the issue of the origin of blue straggler stars in globular and open clusters. We find that for models that include rotation consistent with that observed for some blue straggler stars, evolution is chemically homogeneous. This leads to tracks in the H-R diagram that are brighter and bluer than the non-rotating main-sequence turn-off point. Rotational mixing could thus be one of the factors that contribute to the formation of blue stragglers.

The observation of the polarization emerging from a rotating star at different phases opens up the possibility to map the magnetic field in the stellar surface thanks to the well-known Zeeman–Doppler imaging. When the magnetic field is sufficiently weak, the circular and linear polarization profiles locally in each point of the star are proportional to the first and second derivatives of the unperturbed intensity profile, respectively. We show that the weak-field approximation (for weak lines in the case of linear polarization) can be generalized to the case of a rotating star including the Doppler effect and taking into account the integration on the stellar surface. The Stokes profiles are written as a linear combination of wavelength-dependent terms expressed as series expansions in terms of Hermite polynomials. These terms contain the surface-integrated magnetic field and velocity components. The direct numerical evaluation of these quantities is limited to rotation velocities not larger than eight times the Doppler width of the local absorption profiles. Additionally, we demonstrate that in a rotating star, the circular polarization flux depends on the derivative of the intensity flux with respect to the wavelength and also on the profile itself. Likewise, the linear polarization depends on the profile and on its first and second derivatives with respect to the wavelength. We particularize the general expressions to a rotating dipole.

Zeeman–Doppler imaging studies have shown that the magnetic fields of T Tauri stars can be significantly more complex than a simple dipole and can vary markedly between sources. We collect and summarize the magnetic field topology information obtained to date and present Hertzsprung–Russell (H-R) diagrams for the stars in the sample. Intriguingly, the large-scale field topology of a given pre-main-sequence (PMS) star is strongly dependent upon the stellar internal structure, with the strength of the dipole component of its multipolar magnetic field decaying rapidly with the development of a radiative core. Using the observational data as a basis, we argue that the general characteristics of the global magnetic field of a PMS star can be determined from its position in the H-R diagram. Moving from hotter and more luminous to cooler and less luminous stars across the PMS of the H-R diagram, we present evidence for four distinct magnetic topology regimes. Stars with large radiative cores, empirically estimated to be those with a core mass in excess of ∼40% of the stellar mass, host highly complex and dominantly non-axisymmetric magnetic fields, while those with smaller radiative cores host axisymmetric fields with field modes of higher order than the dipole dominant (typically, but not always, the octupole). Fully convective stars above ≳ 0.5 M_☉ appear to host dominantly axisymmetric fields with strong (kilo-Gauss) dipole components. Based on similarities between the magnetic properties of PMS stars and main-sequence M-dwarfs with similar internal structures, we speculate that a bistable dynamo process operates for lower mass stars (≲ 0.5 M_☉ at an age of a few Myr) and that they will be found to host a variety of magnetic field topologies. If the magnetic topology trends across the H-R diagram are confirmed, they may provide a new method of constraining PMS stellar evolution models.

We present the results of a machine-learning (ML)-based search for new R Coronae Borealis (RCB) stars and DY Persei-like stars (DYPers) in the Galaxy using cataloged light curves from the All-Sky Automated Survey (ASAS) Catalog of Variable Stars (ACVS). RCB stars—a rare class of hydrogen-deficient carbon-rich supergiants—are of great interest owing to the insights they can provide on the late stages of stellar evolution. DYPers are possibly the low-temperature, low-luminosity analogs to the RCB phenomenon, though additional examples are needed to fully establish this connection. While RCB stars and DYPers are traditionally identified by epochs of extreme dimming that occur without regularity, the ML search framework more fully captures the richness and diversity of their photometric behavior. We demonstrate that our ML method can use newly discovered RCB stars to identify additional candidates within the same data set. Our search yields 15 candidates that we consider likely RCB stars/DYPers: new spectroscopic observations confirm that four of these candidates are RCB stars and four are DYPers. Our discovery of four new DYPers increases the number of known Galactic DYPers from two to six; noteworthy is that one of the new DYPers has a measured parallax and is m ≈ 7 mag, making it the brightest known DYPer to date. Future observations of these new DYPers should prove instrumental in establishing the RCB connection. We consider these results, derived from a machine-learned probabilistic classification catalog, as an important proof-of-concept for the efficient discovery of rare sources with time-domain surveys.

Transport by meridional flows has significant consequences for stellar evolution, but is difficult to capture in global-scale numerical simulations because of the wide range of timescales involved. Stellar evolution models therefore usually adopt parameterizations for such transport based on idealized laminar or mean-field models. Unfortunately, recent attempts to model this transport in global simulations have produced results that are not consistent with any of these idealized models. In an effort to explain the discrepancies between global simulations and idealized models, here we use three-dimensional local Cartesian simulations of compressible convection to study the efficiency of transport by meridional flows below a convection zone in several parameter regimes of relevance to the Sun and solar-type stars. In these local simulations we are able to establish the correct ordering of dynamical timescales, although the separation of the timescales remains unrealistic. We find that, even though the generation of internal waves by convective overshoot produces a high degree of time dependence in the meridional flow field, the mean flow has the qualitative behavior predicted by laminar, "balanced" models. In particular, we observe a progressive deepening, or "burrowing," of the mean circulation if the local Eddington–Sweet timescale is shorter than the viscous diffusion timescale. Such burrowing is a robust prediction of laminar models in this parameter regime, but has never been observed in any previous numerical simulation. We argue that previous simulations therefore underestimate the transport by meridional flows.

We present radio continuum (1.3 and 3.6 cm) and H₂O maser observations toward the high-mass star-forming region IRAS 23033+5951 carried out with the VLA–EVLA (in transition phase) in the A configuration. Three radio continuum sources are detected at 3.6 cm, which are aligned in the east–west direction. However, no continuum emission is detected in the region at 1.3 cm. Based on the continuum information, we find that the two continuum sources detected in the region could be consistent with ultracompact H ii regions harboring ZAMS B2 and B2.5 stars; however, we do not rule out that they could be associated with a radio jet. In addition, nine water maser spots are detected toward IRAS 23033+5951, which are clustered in two groups and located about 2'' to the south of the continuum sources. The spatio-kinematical distribution of the water masers suggests that they are tracing a circumstellar disk associated with a central star ZAMS B0, which could be the least evolved source in the region and has not developed an H ii region yet. Moreover, as the circumstellar disk seems to be associated with the CO molecular outflow observed in the region, this conforms to a disk-YSO-outflow system, similar to that found in low-mass stars.

Aiming at obtaining detailed information on the surface environment of Earth analogs, Kawahara & Fujii proposed an inversion technique of annual scattered light curves named spin–orbit tomography (SOT), which enables us to sketch a two-dimensional albedo map from annual variation of the disk-integrated scattered light, and demonstrated the method with a planet in a face-on orbit. We extend it to be applicable to general geometric configurations, including low-obliquity planets like the Earth in inclined orbits. We simulate light curves of the Earth in an inclined orbit in three photometric bands (0.4–0.5 μm, 0.6–0.7 μm, and 0.8–0.9 μm) and show that the distribution of clouds, snow, and continents is retrieved with the aid of the SOT. We also demonstrate the SOT by applying it to an upright Earth, a tidally locked Earth, and Earth analogs with ancient continental configurations. The inversion is model independent in the sense that we do not assume specific albedo models when mapping the surface, and hence applicable in principle to any kind of inhomogeneity. This method can potentially serve as a unique tool to investigate the exohabitats/exoclimes of Earth analogs.

Because of the development of large-format, wide-field cameras, microlensing surveys are now able to monitor millions of stars with sufficient cadence to detect planets. These new discoveries will span the full range of significance levels including planetary signals too small to be distinguished from the noise. At present, we do not understand where the threshold is for detecting planets. MOA-2011-BLG-293Lb is the first planet to be published from the new surveys, and it also has substantial follow-up observations. This planet is robustly detected in survey+follow-up data (Δχ² ∼ 5400). The planet/host mass ratio is q = (5.3 ± 0.2) × 10⁻³. The best-fit projected separation is s = 0.548 ± 0.005 Einstein radii. However, due to the s↔s⁻¹ degeneracy, projected separations of s⁻¹ are only marginally disfavored at Δχ² = 3. A Bayesian estimate of the host mass gives M_L = 0.43^+0.27_{− 0.17} M_☉, with a sharp upper limit of M_L < 1.2 M_☉ from upper limits on the lens flux. Hence, the planet mass is m_p = 2.4^+1.5_{− 0.9} M_Jup, and the physical projected separation is either r_⊥ ≃ 1.0 AU or r_⊥ ≃ 3.4 AU. We show that survey data alone predict this solution and are able to characterize the planet, but the Δχ² is much smaller (Δχ² ∼ 500) than with the follow-up data. The Δχ² for the survey data alone is smaller than for any other securely detected planet. This event suggests a means to probe the detection threshold, by analyzing a large sample of events like MOA-2011-BLG-293, which have both follow-up data and high-cadence survey data, to provide a guide for the interpretation of pure survey microlensing data.

It has been posited that lunar eclipse observations may help predict the in-transit signature of Earth-like extrasolar planets. However, a comparative analysis of the two phenomena addressing in detail the transport of stellar light through the planet's atmosphere has not yet been presented. Here, we proceed with the investigation of both phenomena by making use of a common formulation. Our starting point is a set of previously unpublished near-infrared spectra collected at various phases during the 2008 August lunar eclipse. We then take the formulation to the limit of an infinitely distant observer in order to investigate the in-transit signature of the Earth–Sun system as being observed from outside our solar system. The refraction bending of sunlight rays that pass through Earth's atmosphere is a critical factor in the illumination of the eclipsed Moon. Likewise, refraction will have an impact on the in-transit transmission spectrum for specific planet–star systems depending on the refractive properties of the planet's atmosphere, the stellar size, and the planet's orbital distance. For the Earth–Sun system, at mid-transit, refraction prevents the remote observer's access to the lower ∼12–14 km of the atmosphere and, thus, also to the bulk of the spectroscopically active atmospheric gases. We demonstrate that the effective optical radius of the Earth in-transit is modulated by refraction and varies by ∼12 km from mid-transit to internal contact. The refractive nature of atmospheres, a property which is rarely accounted for in published investigations, will pose additional challenges to the characterization of Earth-like extrasolar planets. Refraction may have a lesser impact for Earth-like extrasolar planets within the habitable zone of some M-type stars.

We present 2''–10'' imaging of 11 transitions from 9 molecular species across the nuclear bar in Maffei 2. The data were obtained with the BIMA and OVRO interferometers. The 10 detected transitions are compared with existing CO isotopologues, HCN, CS, and millimeter continuum data. Dramatic spatial variations among the mapped species are observed across the nuclear bar. A principal component analysis is performed to characterize correlations between the transitions, star formation, and molecular column density. The analysis reveals that HCN, HNC, HCO⁺, and 3 mm continuum are tightly correlated, indicating a direct connection to massive star formation. We find two main morphologically distinct chemical groups, CH₃OH, SiO, and HNCO comprising the grain chemistry molecules, versus HCN, HNC, HCO⁺, and C₂H, molecules strong in the presence of star formation. The grain chemistry molecules, HNCO, CH₃OH, and SiO, trace hydrodynamical bar shocks. The near constancy of the HNCO/CH₃OH, SiO/CH₃OH, and SiO/HNCO ratios argues that shock properties are uniform across the nucleus. HCN/HCO⁺, HCN/HNC, HCN/CS, and HCN/CO ratios are explained primarily by variations in density. High HCO⁺/N₂H⁺ ratios are correlated with the C₂H line, suggesting that this ratio may be a powerful new dense photon-dominated region probe in external galaxies. C₂H reveals a molecular outflow along the minor axis. The morphology and kinematics of the outflow are consistent with an outflow age of 6–7 Myr.

This paper examines star formation (SF) in relatively massive, primarily early-type galaxies (ETGs) at z ∼ 0.1. A sample is drawn from bulge-dominated Galaxy Evolution Explorer/Sloan Digital Sky Survey (GALEX/SDSS) galaxies on the optical red sequence with strong UV excess and yet quiescent SDSS spectra. High-resolution far-UV imaging of 27 such ETGs using Hubble Space Telescope Advanced Camera for Surveys/Solar Blind Channel (ACS/SBC) reveals structured UV morphology in 93% of the sample, consistent with low-level ongoing SF (∼0.5 M_☉ yr⁻¹). In 3/4 of the sample the SF is extended on galaxy scales (25–75 kpc), while the rest contains smaller (5–15 kpc) SF patches in the vicinity of an ETG—presumably gas-rich satellites being disrupted. Optical imaging reveals that all ETGs with galaxy-scale SF in our sample have old stellar disks (mostly S0 type). None is classified as a true elliptical. In our sample, galaxy-scale SF takes the form of UV rings of varying sizes and morphologies. For the majority of such objects we conclude that the gas needed to fuel current SF has been accreted from the intergalactic medium, probably in a prolonged, quasi-static manner, leading in some cases to additional disk buildup. The remaining ETGs with galaxy-scale SF have UV and optical morphologies consistent with minor merger-driven SF or with the final stages of SF in fading spirals. Our analysis excludes that all recent SF on the red sequence resulted from gas-rich mergers. We find further evidence that galaxy-scale SF is almost exclusively an S0 phenomenon (∼20% S0s have SF) by examining the overall optically red SDSS ETGs. Conclusion is that significant number of field S0s maintain or resume low-level SF because the preventive feedback is not in place or is intermittent. True ellipticals, on the other hand, stay entirely quiescent even in the field.

The physical relationship between the far-infrared and radio fluxes of star-forming galaxies has yet to be definitively determined. The favored interpretation, the "calorimeter model," requires that supernova generated cosmic-ray (CR) electrons cool rapidly via synchrotron radiation. However, this cooling should steepen their radio spectra beyond what is observed, and so enhanced ionization losses at low energies from high gas densities are also required. Further, evaluating the minimum energy magnetic field strength with the traditional scaling of the synchrotron flux may underestimate the true value in massive starbursts if their magnetic energy density is comparable to the hydrostatic pressure of their disks. Gamma-ray spectra of starburst galaxies, combined with radio data, provide a less ambiguous estimate of these physical properties in starburst nuclei. While the radio flux is most sensitive to the magnetic field, the GeV gamma-ray spectrum normalization depends primarily on gas density. To this end, spectra above 100 MeV were constructed for two nearby starburst galaxies, NGC 253 and M82, using Fermi data. Their nuclear radio and far-infrared spectra from the literature are compared to new models of the steady-state CR distributions expected from starburst galaxies. Models with high magnetic fields, favoring galaxy calorimetry, are overall better fits to the observations. These solutions also imply relatively high densities and CR ionization rates, consistent with molecular cloud studies.

We present our XMM-Newton observation of the fastest rotating spiral galaxy UGC 12591. We detect hot gas halo emission out to 80 kpc from the galaxy center, and constrain the halo gas mass to be smaller than 4.5 × 10¹¹ M_☉. We also measure the temperature of the hot gas as T = 0.64 ± 0.03 keV. Combining our x-ray constraints and the near-infrared and radio measurements in the literature, we find a baryon mass fraction of 0.03–0.05 in UGC 12591, suggesting a missing baryon mass of 70% compared with the cosmological mean value. Combined with another recent measurement in NGC 1961, the result strongly argues that the majority of missing baryons in spiral galaxies do not reside in their hot halos. We also find that UGC 12591 lies significantly below the baryonic Tully–Fisher relationship. Finally, we find that the baryon fractions of massive spiral galaxies are similar to those of galaxy groups with similar masses, indicating that the baryon loss is ultimately controlled by the gravitational potential well. The cooling radius of this gas halo is small, similar to NGC 1961, which argues that the majority of the stellar mass of this galaxy is not assembled as a result of cooling of this gas halo.

If a component of cosmological dark matter is made up of massive particles—such as sterile neutrinos—that decay with cosmological lifetime to emit photons, the reionization history of the universe would be affected, and cosmic microwave background anisotropies can be used to constrain such a decaying particle model of dark matter. The optical depth depends rather sensitively on the decaying dark matter particle mass m_dm, lifetime τ_dm, and the mass fraction of cold dark matter f that they account for in this model. Assuming that there are no other sources of reionization and using the Wilkinson Microwave Anisotropy Probe 7-year data, we find that 250 eV ≲ m_dm ≲ 1 MeV, whereas 2.23 × 10³ yr ≲ τ_dm/f ≲ 1.23 × 10¹⁸ yr. The best-fit values for m_dm and τ_dm/f are 17.3 keV and 2.03 × 10¹⁶ yr, respectively.

Electron accelerations at high Mach number collisionless shocks are investigated by means of two-dimensional electromagnetic particle-in-cell simulations with various Alfvén Mach numbers, ion-to-electron mass ratios, and the upstream electron β_e (the ratio of the thermal pressure to the magnetic pressure). We find electrons are effectively accelerated at a super-high Mach number shock (M_A ∼ 30) with a mass ratio of M/m = 100 and β_e = 0.5. The electron shock surfing acceleration is an effective mechanism for accelerating the particles toward the relativistic regime even in two dimensions with a large mass ratio. Buneman instability excited at the leading edge of the foot in the super-high Mach number shock results in a coherent electrostatic potential structure. While multi-dimensionality allows the electrons to escape from the trapping region, they can interact with the strong electrostatic field several times. Simulation runs in various parameter regimes indicate that the electron shock surfing acceleration is an effective mechanism for producing relativistic particles in extremely high Mach number shocks in supernova remnants, provided that the upstream electron temperature is reasonably low.

We report four years of radio and X-ray monitoring of the Type IIn supernova SN 2006jd at radio wavelengths with the Very Large Array, Giant Metrewave Radio Telescope, and Expanded Very Large Array; at X-ray wavelengths with Chandra, XMM-Newton, and Swift-XRT. We assume that the radio and X-ray emitting particles are produced by shock interaction with a dense circumstellar medium. The radio emission shows an initial rise that can be attributed to free–free absorption by cool gas mixed into the nonthermal emitting region; external free–free absorption is disfavored because of the shape of the rising light curves and the low gas column density inferred along the line of sight to the emission region. The X-ray luminosity implies a preshock circumstellar density ∼10⁶ cm⁻³ at a radius r ∼ 2 × 10¹⁶ cm, but the column density inferred from the photoabsorption of X-rays along the line of sight suggests a significantly lower density. The implication may be an asymmetry in the interaction. The X-ray spectrum shows Fe line emission at 6.9 keV that is stronger than is expected for the conditions in the X-ray emitting gas. We suggest that cool gas mixed into the hot gas plays a role in the line emission. Our radio and X-ray data both suggest the density profile is flatter than r⁻² because of the slow evolution of the unabsorbed emission.

Monte Carlo approaches to radiation transport have several attractive properties such as simplicity of implementation, high accuracy, and good parallel scaling. Moreover, Monte Carlo methods can handle complicated geometries and are relatively easy to extend to multiple spatial dimensions, which makes them potentially interesting in modeling complex multi-dimensional astrophysical phenomena such as core-collapse supernovae. The aim of this paper is to explore Monte Carlo methods for modeling neutrino transport in core-collapse supernovae. We generalize the Implicit Monte Carlo photon transport scheme of Fleck & Cummings and gray discrete-diffusion scheme of Densmore et al. to energy-, time-, and velocity-dependent neutrino transport. Using our 1D spherically-symmetric implementation, we show that, similar to the photon transport case, the implicit scheme enables significantly larger timesteps compared with explicit time discretization, without sacrificing accuracy, while the discrete-diffusion method leads to significant speed-ups at high optical depth. Our results suggest that a combination of spectral, velocity-dependent, Implicit Monte Carlo and discrete-diffusion Monte Carlo methods represents a robust approach for use in neutrino transport calculations in core-collapse supernovae. Our velocity-dependent scheme can easily be adapted to photon transport.

The present paper provides a possible explanation for the solar wind electron velocity distribution functions possessing asymmetric energetic tails. By numerically solving the electrostatic weak turbulence equations that involve nonlinear interactions among electrons, Langmuir waves, and ion-sound waves, it is shown that different ratios of ion-to-electron temperatures lead to the generation of varying degrees of asymmetric tails. The present finding may be applicable to observations in the solar wind near 1 AU and in other regions of the heliosphere and interplanetary space.

Quasi-periodic pulsations (QPPs) of flaring emission with periods from a few seconds to tens of minutes have been widely detected from radio bands to γ-ray emissions. However, in the past the spatial information of pulsations could not be utilized well due to the instrument limits. We report here imaging observations of the QPPs in three loop sections during a C1.7 flare with periods of P = 24 s–3 minutes by means of the extreme-ultraviolet 171 Å channel of the Atmospheric Imaging Assembly (AIA) instrument on board the Solar Dynamics Observatory. We confirm that the QPPs with the shortest period of 24 s were not of an artifact produced by the Nyquist frequency of the AIA 12 s cadence. The QPPs in the three loop sections were interconnected and closely associated with the flare. The detected perturbations propagated along the loops at speeds of 65–200 km s⁻¹, close to those of acoustic waves in them. The loops were made up of many bright blobs arranged in alternating bright and dark changes in intensity (spatial periodical distribution) with the wavelengths 2.4–5 Mm (as if they were magnetohydrodynamic waves). Furthermore, in the time–distance diagrams, the detected perturbation wavelengths of the QPPs are estimated to be ∼10 Mm, which evidently do not fit the above ones of the spatial periodic distributions and produce a difference of a factor of 2–4 with them. It is suggested that the short QPPs with periods P < 60 s were possibly sausage-mode oscillations and the long QPPs with periods P > 60 s were the higher (e.g., >2nd) harmonics of slow magnetoacoustic waves.

Using test-particle simulations, we investigate the temporal dependence of the two-point velocity correlation function for charged particles scattering in a time-independent spatially fluctuating magnetic field derived from a three-dimensional isotropic turbulence power spectrum. Such a correlation function allowed us to compute the spatial coefficients of diffusion both parallel and perpendicular to the average magnetic field. Our simulations confirm the dependence of the perpendicular diffusion coefficient on turbulence energy density and particle energy predicted previously by a model for early-time charged particle transport. Using the computed diffusion coefficients, we exploit the particle velocity autocorrelation to investigate the timescale over which the particles "decorrelate" from the solution to the unperturbed equation of motion. Decorrelation timescales are evaluated for parallel and perpendicular motions, including the drift of the particles from the local magnetic field line. The regimes of strong and weak magnetic turbulence are compared for various values of the ratio of the particle gyroradius to the correlation length of the magnetic turbulence. Our simulation parameters can be applied to energetic particles in the interplanetary space, cosmic rays at the supernova shocks, and cosmic-rays transport in the intergalactic medium.

We present the vertical kinematics of stars in the Milky Way's stellar disk inferred from Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding and Exploration (SDSS/SEGUE) G-dwarf data, deriving the vertical velocity dispersion, σ_z, as a function of vertical height |z| and Galactocentric radius R for a set of "mono-abundance" sub-populations of stars with very similar elemental abundances [α/Fe] and [Fe/H]. We find that all mono-abundance components exhibit nearly isothermal kinematics in |z|, and a slow outward decrease of the vertical velocity dispersion: σ_z(z, R | [α/Fe], [Fe/H]) ≈ σ_z([α/Fe], [Fe/H]) × exp (− (R − R₀)/7 kpc). The characteristic velocity dispersions of these components vary from ∼15 km s⁻¹ for chemically young, metal-rich stars with solar [α/Fe], to ≳ 50 km s⁻¹ for metal-poor stars that are strongly [α/Fe]-enhanced, and hence presumably very old. The mean σ_z gradient (dσ_z/dz) away from the mid-plane is only 0.3 ± 0.2 km s⁻¹ kpc⁻¹. This kinematic simplicity of the mono-abundance components mirrors their geometric simplicity; we have recently found their density distribution to be simple exponentials in both the z- and R-directions. We find a continuum of vertical kinetic temperatures (∝σ²_z) as a function of ([α/Fe], [Fe/H]), which contribute to the total stellar surface-mass density approximately as $\Sigma _{R_0}(\sigma ^2_z)\propto \exp (-\sigma ^2_z)$. This and the existence of isothermal mono-abundance populations with intermediate dispersions (30–40 km s⁻¹) reject the notion of a thin–thick-disk dichotomy. This continuum of disk components, ranging from old, "hot," and centrally concentrated ones to younger, cooler, and radially extended ones, argues against models where the thicker disk portions arise from massive satellite infall or heating; scenarios where either the oldest disk portion was born hot, or where internal evolution plays a major role, seem the most viable. In addition, the wide range of σ_z([α/Fe], [Fe/H]) combined with a constant σ_z(z) for each abundance bin provides an independent check on the precision of the SEGUE-derived abundances: δ_[α/Fe] ≈ 0.07 dex and δ_[Fe/H] ≈ 0.15 dex. The slow radial decline of the vertical dispersion presumably reflects the decrease in disk surface-mass density. This measurement constitutes a first step toward a purely dynamical estimate of the mass profile of the stellar and gaseous disk in our Galaxy.

Recent simulations of cluster formation have demonstrated that condensation of baryons into central galaxies during cluster formation can drive the shape of the gas distribution in galaxy clusters significantly rounder out to their virial radius. These simulations generally predict stellar fractions within cluster virial radii that are ∼2–3 times larger than the stellar masses deduced from observations. In this paper, we compare ellipticity profiles of simulated clusters performed with varying input physics (radiative cooling, star formation, and supernova feedback) to the cluster ellipticity profiles derived from Chandra and ROSAT observations, in an effort to constrain the fraction of gas that cools and condenses into the central galaxies within clusters. We find that local relaxed clusters have an average ellipticity of = 0.18 ± 0.05 in the radial range of 0.04 ⩽ r/r₅₀₀ ⩽ 1. At larger radii r > 0.1r₅₀₀, the observed ellipticity profiles agree well with the predictions of non-radiative simulations. In contrast, the ellipticity profiles of simulated clusters that include dissipative gas physics deviate significantly from the observed ellipticity profiles at all radii. The dissipative simulations overpredict (underpredict) ellipticity in the inner (outer) regions of galaxy clusters. By comparing simulations with and without dissipative gas physics, we show that gas cooling causes the gas distribution to be more oblate in the central regions, but makes the outer gas distribution more spherical. We find that late-time gas cooling and star formation are responsible for the significantly oblate gas distributions in cluster cores, but the gas shapes outside of cluster cores are set primarily by baryon dissipation at high redshift (z ⩾ 2). Our results indicate that the shapes of X-ray emitting gas in galaxy clusters, especially at large radii, can be used to place constraints on cluster gas physics, making it potential probes of the history of baryonic cooling in galaxy clusters.

Star formation in galaxies is observed to be associated with gamma-ray emission, presumably from non-thermal processes connected to the acceleration of cosmic-ray nuclei and electrons. The detection of gamma rays from starburst galaxies by the Fermi Large Area Telescope (LAT) has allowed the determination of a functional relationship between star formation rate and gamma-ray luminosity. Since star formation is known to scale with total infrared (8–1000 μm) and radio (1.4 GHz) luminosity, the observed infrared and radio emission from a star-forming galaxy can be used to quantitatively infer the galaxy's gamma-ray luminosity. Similarly, star-forming galaxies within galaxy clusters allow us to derive lower limits on the gamma-ray emission from clusters, which have not yet been conclusively detected in gamma rays. In this study, we apply the functional relationships between gamma-ray luminosity and radio and IR luminosities of galaxies derived by the Fermi Collaboration to a sample of the best candidate galaxy clusters for detection in gamma rays in order to place lower limits on the gamma-ray emission associated with star formation in galaxy clusters. We find that several clusters have predicted gamma-ray emission from star formation that are within an order of magnitude of the upper limits derived in Ackermann et al. based on non-detection by Fermi-LAT. Given the current gamma-ray limits, star formation likely plays a significant role in the gamma-ray emission in some clusters, especially those with cool cores. We predict that both Fermi-LAT over the course of its lifetime and the future Cerenkov Telescope Array will be able to detect gamma-ray emission from star-forming galaxies in clusters.

We present observations of the BL Lac object 1ES 0414+009 in the >200 GeV gamma-ray band by the VERITAS array of Cherenkov telescopes. 1ES 0414+009 was observed by VERITAS between 2008 January and 2011 February, resulting in 56.2 hr of good quality pointed observations. These observations resulted in a detection of 822 events from the source corresponding to a statistical significance of 6.4 standard deviations (6.4σ) above the background. The source flux, showing no evidence for variability, is measured as (5.2 ± 1.1_stat ± 2.6_sys) × 10⁻¹² photons cm⁻² s⁻¹ above 200 GeV, equivalent to approximately 2% of the Crab Nebula flux above this energy. The differential photon spectrum from 230 GeV to 850 GeV is well fit by a power law with a photon index of Γ = 3.4 ± 0.5_stat ± 0.3_sys and a flux normalization of (1.6 ± 0.3_stat ± 0.8_sys) × 10⁻¹¹ photons cm⁻² s⁻¹ at 300 GeV. We also present multiwavelength results taken in the optical (MDM), x-ray (Swift-XRT), and GeV (Fermi-LAT) bands and use these results to construct a broadband spectral energy distribution (SED). Modeling of this SED indicates that homogenous one-zone leptonic scenarios are not adequate to describe emission from the system, with a lepto-hadronic model providing a better fit to the data.

Laboratory evidence suggests that recombination of adsorbed radicals may cause an abrupt temperature excursion of a dust grain to about 1000 K. One consequence of this is the rapid desorption of adsorbed H₂ molecules with excitation temperatures of this magnitude. We compute the consequences of injection of hot H₂ into cold diffuse interstellar gas at a rate of 1% of the canonical H₂ formation rate. We find that the level populations of H₂ in J = 3, 4, and 5 are close to observed values, and that the abundances of CH⁺ and OH formed in reactions with hot hydrogen are close to the values obtained from observations of diffuse clouds.

We propose to evaluate the contribution of polycyclic aromatic hydrocarbon (PAH) molecules that carry side groups to the mid-infrared emission spectra. Within this framework, the IR absorption spectra of 2-vinylanthracene (2-VA) and 9-vinylanthracene (9-VA) were measured in Ar matrices at 12 K and in CsI and polyethylene pellets at room temperature. The laboratory spectra were analyzed with the support of simulations based on the density functional theory. For each PAH molecule, eight IR spectra were computed by combining the B3LYP functional with as many different basis sets, namely, 4-31G, 4-31G(d), 6-31G, 6-311G, 6-31G(d), 6-31G(d,p), 6-31+G(d,p), and 6-31++G(d,p). The comparison of the theoretical spectra with the laboratory data allowed us to determine the most suitable combinations for modeling the IR spectra of neutral PAH molecules that carry a vinyl side group. It was concluded from the examples of 2- and 9-VA that the optimum basis set is 6-31G unless a steric interaction has to be taken into account, in which case the optimum basis set is 6-31G(d). Thus, in the presence of such an interaction, the use of d-type polarization functions is recommended. We discuss the possibility for neutral vinyl-substituted PAHs to contribute to the mid-infrared emission spectra and find that their specific features do not match with the mid-infrared aromatic emission bands.

A collisionless shock may be strongly modified by the presence of neutral atoms through the processes of charge exchange between ions and neutrals and ionization of the latter. These two processes lead to exchange of energy and momentum between charged and neutral particles both upstream and downstream of the shock. In particular, neutrals that suffer a charge exchange downstream with shock-heated ions generate high-velocity neutrals that have a finite probability of returning upstream. These neutrals might then deposit heat in the upstream plasma through ionization and charge exchange, thereby reducing the fluid Mach number. A consequence of this phenomenon, which we refer to as the neutral return flux, is a reduction of the shock compression factor and the formation of a shock precursor upstream. The scale length of the precursor is determined by the ionization and charge-exchange interaction lengths of fast neutrals moving toward upstream infinity. In the case of a shock propagating in the interstellar medium, the effects of ion–neutral interactions are especially important for shock velocities <3000 km s⁻¹. Such propagation velocities are common among shocks associated with supernova remnants, the primary candidate sources for the acceleration of Galactic cosmic rays. We then investigate the effects of the return flux of neutrals on the spectrum of test particles accelerated at the shock. We find that, for shocks slower than ∼3000 km s⁻¹, the particle energy spectrum steepens appreciably with respect to the naive expectation for a strong shock, namely, ∝E⁻².

We introduce the numbers of hot and cold spots, n_h and n_c, of excursion sets of the cosmic microwave background (CMB) temperature anisotropy maps as statistical observables that can discriminate different non-Gaussian models. We numerically compute them from simulations of non-Gaussian CMB temperature fluctuation maps. The first kind of non-Gaussian model we study is the local type primordial non-Gaussianity. The second kind of model has some specific form of the probability distribution function from which the temperature fluctuation value at each pixel is drawn, obtained using HEALPIX. We find the characteristic non-Gaussian deviation shapes of n_h and n_c, which is distinct for each of the models under consideration. We further demonstrate that n_h and n_c carry additional information compared to the genus, which is just their linear combination, making them valuable additions to the Minkowski Functionals in constraining non-Gaussianity.

Approximately 30% of all massive stars in the Galaxy are runaways with velocities exceeding 30 km s⁻¹. Their high speeds allow them to travel ∼0.1–1 kpc away from their birthplace before they explode at the end of their several Myr lifetimes. At high redshift, when galaxies were much smaller than in the local universe, runaways could venture far from the dense inner regions of their host galaxies. From these large radii, and therefore low column densities, much of their ionizing radiation is able to escape into the intergalactic medium. Runaways may therefore significantly enhance the overall escape fraction of ionizing radiation, f_esc, from small galaxies at high redshift. We present simple models of the high-redshift runaway population and its impact on f_esc as a function of halo mass, size, and redshift. We find that the inclusion of runaways enhances f_esc by factors of ≈1.1–8, depending on halo mass, galaxy geometry, and the mechanism of runaway production, implying that runaways may contribute 50%–90% of the total ionizing radiation escaping from high-redshift galaxies. Runaways may therefore play an important role in reionizing the universe.

We have evaluated the contribution of the active galactic nuclei (AGN) population to the ionization history of the universe based on a semi-analytic model of galaxy formation and evolution in the cold dark matter cosmological scenario. The model connects the growth of black holes and of the ensuing AGN activity to galaxy interactions. In the model we have included a self-consistent physical description of the escape of ionizing UV photons; this is based on the blast-wave model for the AGN feedback we developed in a previous paper to explain the distribution of hydrogen column densities in AGNs of various redshifts and luminosities, due to absorption by the host galaxy gas. The model predicts UV luminosity functions for AGNs that are in good agreement with those derived from the observations especially at low and intermediate redshifts (z ∼ 3). At higher redshifts (z  >  5), the model tends to overestimate the data at faint luminosities. Critical biases in both the data and in the model are discussed to explain such apparent discrepancies. The predicted hydrogen photoionization rate as a function of redshift is found to be consistent with that derived from the observations. All of the above suggests that we should reconsider the role of the AGNs as the main driver of the ionization history of the universe.

We use Type Ia supernovae (SNe Ia) discovered by the Sloan Digital Sky Survey-II SN Survey to search for dependencies between SN Ia properties and the projected distance to the host-galaxy center, using the distance as a proxy for local galaxy properties (local star formation rate, local metallicity, etc.). The sample consists of almost 200 spectroscopically or photometrically confirmed SNe Ia at redshifts below 0.25. The sample is split into two groups depending on the morphology of the host galaxy. We fit light curves using both MLCS2k2 and SALT2, and determine color (A_V, c) and light-curve shape (Δ, x₁) parameters for each SN Ia, as well as its residual in the Hubble diagram. We then correlate these parameters with both the physical and the normalized distances to the center of the host galaxy and look for trends in the mean values and scatters of these parameters with increasing distance. The most significant (at the 4σ level) finding is that the average fitted A_V from MLCS2k2 and c from SALT2 decrease with the projected distance for SNe Ia in spiral galaxies. We also find indications that supernovae (SNe) in elliptical galaxies tend to have narrower light curves if they explode at larger distances, although this may be due to selection effects in our sample. We do not find strong correlations between the residuals of the distance moduli with respect to the Hubble flow and the galactocentric distances, which indicates a limited correlation between SN magnitudes after standardization and local host metallicity.

A new code for following the evolution and emissions of proto-neutron stars during the first minute of their lives is developed and tested. The code is one dimensional, fully implicit, and general relativistic. Multi-group, multi-flavor neutrino transport is incorporated that makes use of variable Eddington factors obtained from a formal solution of the static general relativistic Boltzmann equation with linearized scattering terms. The timescales of neutrino emission and spectral evolution obtained using the new code are broadly consistent with previous results. Unlike other recent calculations, however, the new code predicts that the neutrino-driven wind will be characterized, at least for part of its existence, by a neutron excess. This change, potentially consequential for nucleosynthesis in the wind, is due to an improved treatment of the charged current interactions of electron-flavored neutrinos and anti-neutrinos with nucleons. A comparison is also made between the results obtained using either variable Eddington factors or simple equilibrium flux-limited diffusion. The latter approximation, which has been frequently used in previous studies of proto-neutron star cooling, accurately describes the total neutrino luminosities (to within 10%) for most of the evolution, until the proto-neutron star becomes optically thin.

Synchrotron self-Compton (SSC) emission from a reverse shock has been suggested as the origin for the high-energy component lasting 2 s in the prompt phase of GRB98080923. The model describes spectral indices, fluxes, and the duration of the high-energy component as well as a long keV tail present in the prompt phase of GRB980923. Here, we present an extension of this model to describe the high-energy emission of GRB090926A. We argue that the emission consists of two components, one with a duration less than 1 s during the prompt phase, and a second, longer-lasting GeV phase lasting hundred of seconds after the prompt phase. The short high-energy phase can be described as SSC emission from a reverse shock similar to that observed in GRB980923, while the longer component arises from the forward shock. The main assumption is that the jet is magnetized and evolves in the thick-shell case, and the calculated fluxes and break energies are all consistent with the observed values. A comparison between the resulting parameters obtained for GRB980923 and GRB090926A suggests differences in burst tails that could be attributable to the circumburst medium, and this could account for previous analyses reported in the literature for other bursts. We find that the density of the surrounding medium inferred from the observed values associated with the forward shock agrees with standard values for host galaxies such as the one associated with GRB090926A.

We examine in detail the proposition that GW Vir pulsators owe their existence to a residual stellar wind that competes against the settling of the carbon and oxygen atoms which "fuel" pulsational instabilities via their opacity. With cooling, the fading wind progressively loses its capacity to maintain enough of these opaque atoms in the driving region, leading naturally to a red edge where pulsations disappear. We investigate, in particular, the effects of changing the mass-loss law and the initial envelope composition on the position of the red edge in the log g–T_eff diagram. With this approach, we derive a coherent picture of the GW Vir instability domain.

The planetary nebula A30 is believed to have undergone a very late thermal pulse resulting in the ejection of knots of hydrogen-poor material. Using multi-epoch Hubble Space Telescope images, we have detected the angular expansion of these knots and derived an age of 850⁺²⁸⁰_{− 150} yr. To investigate the spectral and spatial properties of the soft X-ray emission detected by ROSAT, we have obtained Chandra and XMM-Newton deep observations of A30. The X-ray emission from A30 can be separated into two components: a point source at the central star and diffuse emission associated with the hydrogen-poor knots and the cloverleaf structure inside the nebular shell. To help us assess the role of the current stellar wind in powering this X-ray emission, we have determined the stellar parameters and wind properties of the central star of A30 using a non-LTE model fit to its optical and UV spectra. The spatial distribution and spectral properties of the diffuse X-ray emission are highly suggestive that it is generated by the post-born-again and present fast stellar winds interacting with the hydrogen-poor ejecta of the born-again event. This emission can be attributed to shock-heated plasma, as the hydrogen-poor knots are ablated by the stellar winds, under which circumstances the efficient mass loading of the present fast stellar wind raises its density and damps its velocity to produce the observed diffuse soft X-rays. Charge transfer reactions between the ions of the stellar winds and material of the born-again ejecta have also been considered as a possible mechanism for the production of diffuse X-ray emission, and upper limits on the expected X-ray production by this mechanism have been derived. The origin of the X-ray emission from the central star of A30 is puzzling: shocks in the present fast stellar wind and photospheric emission can be ruled out, while the development of a new, compact hot bubble confining the fast stellar wind seems implausible.

We present the first resolved map of plane-of-sky magnetic field strength for a quiescent molecular cloud. GRSMC 45.60+0.30 subtends 40 × 10 pc at a distance of 1.88 kpc, masses 16,000 M_☉, and exhibits no star formation. Near-infrared background starlight polarizations were obtained for the Galactic Plane Infrared Polarization Survey using the 1.8 m Perkins telescope and the Mimir instrument. The cloud area of 0.78 deg² contains 2684 significant starlight polarizations for Two Micron All Sky Survey matched stars brighter than 12.5 mag in the H band. Polarizations are generally aligned with the cloud's major axis, showing an average position angle dispersion of 15 ± 2° and polarization of 1.8 ± 0.6%. The polarizations were combined with Galactic Ring Survey ¹³CO spectroscopy and the Chandrasekhar–Fermi method to estimate plane-of-sky magnetic field strengths, with an angular resolution of 100 arcsec. The average plane-of-sky magnetic field strength across the cloud is 5.40 ± 0.04 μG. The magnetic field strength map exhibits seven enhancements or "magnetic cores." These cores show an average magnetic field strength of 8.3 ± 0.9 μG, radius of 1.2 ± 0.2 pc, intercore spacing of 5.7 ± 0.9 pc, and exclusively subcritical mass-to-flux ratios, implying their magnetic fields continue to suppress star formation. The magnetic field strength shows a power-law dependence on gas volume density, with slope 0.75 ± 0.02 for $n_{{\rm H}_2}$ ⩾10 cm⁻³. This power-law index is identical to those in studies at higher densities, but disagrees with predictions for the densities probed here.

As part of the Panchromatic Hubble Andromeda Treasury multi-cycle program, we observed a 12' × 65 area of the bulge of M31 with the WFC3/UVIS filters F275W and F336W. From these data we have assembled a sample of ∼4000 UV-bright, old stars, vastly larger than previously available. We use updated Padova stellar evolutionary tracks to classify these hot stars into three classes: Post-AGB stars (P-AGB), Post-Early AGB (PE-AGB) stars, and AGB-manqué stars. P-AGB stars are the end result of the asymptotic giant branch (AGB) phase and are expected in a wide range of stellar populations, whereas PE-AGB and AGB-manqué (together referred to as the hot post-horizontal branch; HP-HB) stars are the result of insufficient envelope masses to allow a full AGB phase, and are expected to be particularly prominent at high helium or α abundances when the mass loss on the red giant branch is high. Our data support previous claims that most UV-bright sources in the bulge are likely hot (extreme) horizontal branch (EHB) stars and their progeny. We construct the first radial profiles of these stellar populations and show that they are highly centrally concentrated, even more so than the integrated UV or optical light. However, we find that this UV-bright population does not dominate the total UV luminosity at any radius, as we are detecting only the progeny of the EHB stars that are the likely source of the UV excess. We calculate that only a few percent of main-sequence stars in the central bulge can have gone through the HP-HB phase and that this percentage decreases strongly with distance from the center. We also find that the surface density of hot UV-bright stars has the same radial variation as that of low-mass X-ray binaries. We discuss age, metallicity, and abundance variations as possible explanations for the observed radial variation in the UV-bright population.

A model of coupled mantle convection and planetary tectonics is used to demonstrate that history dependence can outweigh the effects of a planet's energy content and material parameters in determining its tectonic state. The mantle convection-surface tectonics system allows multiple tectonic modes to exist for equivalent planetary parameter values. The tectonic mode of the system is then determined by its specific geologic and climatic history. This implies that models of tectonics and mantle convection will not be able to uniquely determine the tectonic mode of a terrestrial planet without the addition of historical data. Historical data exists, to variable degrees, for all four terrestrial planets within our solar system. For the Earth, the planet with the largest amount of observational data, debate does still remain regarding the geologic and climatic history of Earth's deep past but constraints are available. For planets in other solar systems, no such constraints exist at present. The existence of multiple tectonic modes, for equivalent parameter values, points to a reason why different groups have reached different conclusions regarding the tectonic state of extrasolar terrestrial planets larger than Earth ("super-Earths"). The region of multiple stable solutions is predicted to widen in parameter space for more energetic mantle convection (as would be expected for larger planets). This means that different groups can find different solutions, all potentially viable and stable, using identical models and identical system parameter values. At a more practical level, the results argue that the question of whether extrasolar terrestrial planets will have plate tectonics is unanswerable and will remain so until the temporal evolution of extrasolar planets can be constrained.

We obtain estimates of Sgr A* accretion flow and black hole parameters by fitting polarized submillimeter observations with spectra computed using three-dimensional general relativistic (GR) magnetohydrodynamical (MHD) (GRMHD) simulations. Observations are compiled from averages over many epochs from reports in 29 papers for estimating the mean fluxes F_ν, linear polarization (LP) fractions, circular polarization (CP) fractions, and electric vector position angles. GRMHD simulations are computed with dimensionless spins a_* = 0, 0.5, 0.7, 0.9, 0.98 over a 20, 000M time interval. We perform fully self-consistent GR polarized radiative transfer using our new code to explore the effects of spin a_*, inclination angle θ, position angle (P.A.), accretion rate $\dot{M}$, and electron temperature T_e (T_e is reported for radius 6M). By fitting the mean submillimeter fluxes and LP/CP fractions, we obtain estimates for these model parameters and determine the physical effects that could produce polarization signatures. Our best-bet model has a_* = 0.5, θ = 75°, P.A. = 115°, $\dot{M}=4.6\times 10^{-8}\ M_\odot \ {\rm {{\rm yr}}}^{-1}$, and T_e = 3.1 × 10¹⁰ K at 6M. The submillimeter CP is mainly produced by Faraday conversion as modified by Faraday rotation, and the emission region size at 230 GHz is consistent with the very long baseline interferometry size of 37 μas. Across all spins, model parameters are in the ranges θ = 42°–75°, $\dot{M}=(1.4\hbox{--}7.0)\times 10^{-8}\ M_\odot \ {\rm {{\rm yr}}}^{-1}$, and T_e = (3–4) × 10¹⁰ K. Polarization is found both to help differentiate models and to introduce new observational constraints on the effects of the magnetic field that might not be fit by accretion models so far considered.

We report the discovery of two new halo velocity groups (Cancer groups A and B) traced by eight distant RR Lyrae stars and observed by the Palomar Transient Factory survey at R.A. ∼ 129°, decl. ∼ 20° (l ∼ 205°, b ∼ 32°). Located at 92 kpc from the Galactic center (86 kpc from the Sun), these are some of the most distant substructures in the Galactic halo known to date. Follow-up spectroscopic observations with the Palomar Observatory 5.1 m Hale telescope and W. M. Keck Observatory 10 m Keck I telescope indicate that the two groups are moving away from the Galaxy at $\bar{v}^A_{{\rm gsr}} = 78.0\pm 5.6$ km s⁻¹ (Cancer group A) and $\bar{v}^B_{{\rm gsr}} = 16.3\pm 7.1$ km s⁻¹ (Cancer group B). The groups have velocity dispersions of $\sigma ^A_{v_{{\rm gsr}}}=12.4\pm 5.0$ km s⁻¹ and $\sigma ^B_{v_{{\rm gsr}}}=14.9\pm 6.2$ km s⁻¹ and are spatially extended (about several kpc), making it very unlikely that they are bound systems, and more likely to be debris of tidally disrupted dwarf galaxies or globular clusters. Both groups are metal-poor (median metallicities of [Fe/H]^A = −1.6 dex and [Fe/H]^B = −2.1 dex) and have a somewhat uncertain (due to small sample size) metallicity dispersion of ∼0.4 dex, suggesting dwarf galaxies as progenitors. Two additional RR Lyrae stars with velocities consistent with those of the Cancer groups have been observed ∼25° east, suggesting possible extension of the groups in that direction.

Inferences based on interplanetary field measurements have suggested a statistical tendency for the heliospheric current sheet (HCS) to be displaced southward of the heliographic equator during the past four solar cycles. Here, we use synoptic maps of white-light streamer structures to determine more directly the longitudinally averaged latitude of the HCS, after separating out the contribution of streamers without magnetic polarity reversals ("pseudostreamers"). We find a strong tendency for the HCS to be shifted southward by a few degrees during 2007–2011, but no significant shift during the 1996–1997 sunspot minimum. Fluctuations in the magnitude and direction of the north–south shifts often occur on timescales as short as one or two Carrington rotations, as a result of changes in the streamer structures due to active region emergence. The largest shifts occurred during 2010–2011 and were on the order of −6°. Such southward displacements are consistent with the overwhelming dominance of northern-hemisphere sunspot activity during the rising phase of the current solar cycle 24, resulting in a strong axisymmetric quadrupole component whose sign at the equator matched that of the north polar field; the symmetry-breaking effect of the quadrupole was further enhanced by the weakness of the polar fields.

We present one-dimensional hydrodynamical models that suggest a new mechanism for generating spiral structures around evolved stars. In these models, the pulsation of the star initiates the mass outflow and generates shock waves from a static atmosphere. An orbiting companion perturbs the outflow, creating a long-period series of shocks with different speeds and gas density that form spiral arms around the star. The spacing and number of spirals generated are predictable from pulsation and orbital periods. Companions in close orbits create up to four spiral arms, while companions farther out predominantly form single spiral arms. The interaction also produces a variety of density and temperature structures close to the star in the equatorial plane. This study extends the set of mechanisms for explaining the morphologies of protoplanetary nebulae.

Traditional pulsar polarization sweep analysis starts from the point dipole rotating vector model (RVM) approximation. If augmented by a measurement of the sweep phase shift, one obtains an estimate of the emission altitude (Blaskiewicz et al.). However, a more realistic treatment of field line sweepback and finite altitude effects shows that this estimate breaks down at modest altitude ∼0.1 R_LC. Such radio emission altitudes turn out to be relevant to the young energetic and millisecond pulsars that dominate the γ-ray population. We quantify the breakdown height as a function of viewing geometry and provide simple fitting formulae that allow observers to correct RVM-based height estimates, preserving reasonable accuracy to R ∼ 0.3 R_LC. We discuss briefly other observables that can check and improve height estimates.

Following a simulation approach of recent publications, we explore the viability of the neutrino-heating explosion mechanism's dependence on the spatial dimension. Our results disagree with previous findings. While we also observe that two-dimensional (2D) models explode for lower driving neutrino luminosity than spherically symmetric (1D) models, we do not find that explosions in 3D occur easier and earlier than in 2D. Moreover, we find that the average entropy of matter in the gain layer hardly depends on the dimension and thus is not a good diagnostic quantity for the readiness to explode. Instead, mass, integrated entropy, total neutrino-heating rate, and non-radial kinetic energy in the gain layer are higher when models are closer to explosion. Coherent, large-scale mass motions as typically associated with the standing accretion-shock instability (SASI) are observed to be supportive for explosions because they drive strong shock expansion and thus enlarge the gain layer. While 2D models with better angular resolution clearly explode more easily, the opposite trend is seen in 3D. We interpret this as a consequence of the turbulent energy cascade, which transports energy from small to large spatial scales in 2D, thus fostering SASI activity. In contrast, the energy flow in 3D is in the opposite direction, feeding fragmentation and vortex motions on smaller scales and thus making the 3D evolution with finer grid resolution more similar to 1D. More favorable conditions for explosions in 3D may therefore be tightly linked to efficient growth of low-order SASI modes including nonaxisymmetric ones.

A posteriori anisotropy study of ultra-high energy cosmic rays (UHECRs) with the Pierre Auger Observatory (PAO) has shown evidence of an excess of cosmic-ray particles above 55 EeV within 18° of the direction of the radio galaxy Centaurus A. However, the origin of the excess remains elusive. We simulate the propagation of different species of particles coming from the direction of Centaurus A in the Galactic magnetic fields and find that only particles of nuclear charge Z ≲ 10 can avoid being deflected outside of the 18° window of Centaurus A. On the other hand, considering the increasingly heavy composition of UHECRs at the highest energies measured by PAO, a plausible scenario for cosmic rays from the direction of Centaurus A can be found if they consist of intermediate-mass nuclei. The chemical composition of cosmic rays can be further constrained by lower-energy cosmic rays of the same rigidity. We find that cosmic-ray acceleration in the lobes of Centaurus A is not favored, while acceleration in the stellar winds that are rich in intermediate-mass nuclei could meet the requirement. This suggests that the observed excess may originate from cosmic-ray accelerators induced by stellar explosions in the star-forming regions of Centaurus A and/or the Centaurus cluster located behind Centaurus A.

The prompt emission of gamma-ray bursts (GRBs) is usually well described by the Band function: two power laws (PLs) joined smoothly at a given break energy. In addition to the Band component, a few bursts (GRB941017, GRB090510, GRB090902B, and GRB090926A) show clear evidence of a distinct high-energy spectral component, which in some cases evolves independently from the prompt keV component and is well described by a PL, sometimes with a cutoff energy; this component is found to have long duration, even longer than the burst itself for all four bursts. Here we report the observation of an anomalous short duration high-energy component in GRB980923. GRB980923 is one of the brightest GRBs observed by BATSE. Its light curve is characterized by a rapid variability phase lasting ∼40 s, followed by a smooth emission tail lasting ∼400 s. A detailed joint analysis of BATSE (Large Area Detector and Spectroscopy Detector) and EGRET TASC data of GRB980923 reveals the presence of an anomalous keV to MeV component in the spectrum that evolves independently from the prompt keV one. This component is well described by a PL with a spectral index of −1.44 and lasts only ∼2 s; it represents one of the three clearly separated spectral components identified in GRB980923, the other two being the keV prompt emission, well described by the Band function and the tail, well fit by a Smoothly Broken Power Law.

Using the High Resolution Camera on board the Chandra X-ray Observatory, we have re-examined the proper motion of the central compact object RX J0822−4300 in the supernova remnant Puppis A. New data from 2010 August, combined with three archival data sets from as early as 1999 December, provide a baseline of 3886 days (more than 10.5 yr) to perform the measurement. Correlating the four positions of RX J0822−4300 measured in each data set implies a projected proper motion of μ = 71 ± 12  mas yr⁻¹. For a distance of 2 kpc, this proper motion is equivalent to a recoil velocity of 672 ± 115  km s⁻¹. The position angle is found to be 244° ± 11°. Both the magnitude and direction of the proper motion are in agreement with RX J0822−4300 originating near the optical expansion center of the supernova remnant. For a displacement of 371 ± 31 arcsec between its birthplace and today's position, we deduce an age of (5.2 ± 1.0) × 10³ yr for RX J0822−4300. The age inferred from the neutron star proper motion and filament motions can be considered as two independent measurements of the same quantity. They average to 4450 ± 750 yr for the age of the supernova remnant Puppis A.

This manuscript describes the first ensemble of three-dimensional (3D) particle-in-cell (PIC) plasma simulations of whistler turbulence. The computational model represents a collisionless, homogeneous, magnetized plasma on which an initial spectrum of relatively long wavelength whistler fluctuations is imposed. The simulations represent a range of initial fluctuation amplitudes and follow the temporal evolution of the system as it decays into a broadband, anisotropic, turbulent spectrum at shorter wavelengths via a forward cascade. The resulting 3D turbulence is similar in many ways to whistler turbulence from previous two-dimensional (2D) PIC simulations, although the anisotropies in 3D are stronger than in comparable 2D runs. The most important difference is that reduced magnetic fluctuation spectra from the 3D simulations show a clear break in the perpendicular wavenumber (k_⊥) spectra. Spectra at small k_⊥ are relatively steep, but spectra at larger k_⊥ are even steeper, similar in character to magnetic spectra at electron scales recently measured in the solar wind.

We propose to describe the variety of galaxies from the Sloan Digital Sky Survey by using only one affine parameter. To this aim, we construct the principal curve (P-curve) passing through the spine of the data point cloud, considering the eigenspace derived from Principal Component Analysis (PCA) of morphological, physical, and photometric galaxy properties. Thus, galaxies can be labeled, ranked, and classified by a single arc-length value of the curve, measured at the unique closest projection of the data points on the P-curve. We find that the P-curve has a "W" letter shape with three turning points, defining four branches that represent distinct galaxy populations. This behavior is controlled mainly by two properties, namely u − r and star formation rate (from blue young at low arc length to red old at high arc length), while most other properties correlate well with these two. We further present the variations of several important galaxy properties as a function of arc length. Luminosity functions vary from steep Schechter fits at low arc length to double power law and ending in lognormal fits at high arc length. Galaxy clustering shows increasing autocorrelation power at large scales as arc length increases. Cross correlation of galaxies with different arc lengths shows that the probability of two galaxies belonging to the same halo decreases as their distance in arc length increases. PCA analysis allows us to find peculiar galaxy populations located apart from the main cloud of data points, such as small red galaxies dominated by a disk, of relatively high stellar mass-to-light ratio and surface mass density. On the other hand, the P-curve helped us understand the average trends, encoding 75% of the available information in the data. The P-curve allows not only dimensionality reduction but also provides supporting evidence for the following relevant physical models and scenarios in extragalactic astronomy: (1) The hierarchical merging scenario in the formation of a selected group of red massive galaxies. These galaxies present a lognormal r-band luminosity function, which might arise from multiplicative processes involved in this scenario. (2) A connection between the onset of active galactic nucleus activity and star formation quenching as mentioned in Martin et al., which appears in green galaxies transitioning from blue to red populations.

The relation between the ratio of infrared (IR) and ultraviolet (UV) flux densities (the infrared excess: IRX) and the slope of the UV spectrum (β) of galaxies plays a fundamental role in the evaluation of the dust attenuation of star-forming galaxies, especially at high redshifts. Many authors, however, have pointed out that there is a significant dispersion and/or deviation from the originally proposed IRX–β relation depending on sample selection. We reexamined the IRX–β relation by measuring the far- and near-UV flux densities of the original sample galaxies with GALEX and AKARI imaging data and constructed a revised formula. We found that the newly obtained IRX values were lower than the original relation because of the significant underestimation of the UV flux densities of the galaxies, caused by the small aperture of IUE. Furthermore, since the original relation was based on IRAS data that covered a wavelength range of λ = 42–122 μm, we obtained an appropriate IRX–β relation with total dust emission (TIR): log (L_TIR/L_FUV) = log [10^{0.4(3.06 + 1.58β)} − 1] + 0.22 using the data from AKARI, which has wider wavelength coverage toward longer wavelengths. This new relation is consistent with most of the preceding results for samples selected at optical and UV, though there is significant scatter around it. We also found that even the quiescent class of IR galaxies follows this new relation, though luminous and ultraluminous IR galaxies distribute completely differently as previously thought.

We construct axisymmetric mass models for dwarf spheroidal (dSph) galaxies in the Milky Way to obtain plausible limits on the non-spherical structure of their dark halos. This is motivated by the fact that the observed luminous parts of the dSphs are actually non-spherical and cold dark matter models predict non-spherical virialized dark halos. Our models consider velocity anisotropy of stars $\overline{v^2_R}{/}\overline{v^2_{\phi }}$, which can vary with the adopted cylindrical coordinates under the assumption $\overline{v^2_z}=\overline{v^2_R}$ for simplicity, and also include an inclination of the system as a fitting parameter to explain the observed line-of-sight velocity dispersion profile. Applying these models to six of the bright dSphs in the Milky Way, we find that the best-fitting cases for most of the dSphs yield oblate and flattened dark halos, irrespective of assumed density profiles in their central parts. We also find that the total mass of the dSphs enclosed within a spheroid with major-axis length of 300 pc varies from 10⁶ M_☉ to 10⁷ M_☉, contrary to the conclusion from spherical models. This suggests the importance of considering shapes of dark halos in mass models of the dSphs. It is also found that dark halos of the Galactic dSphs may be more flattened than N-body predictions, thereby implying our yet incomplete understanding of baryonic and/or non-baryonic dark matter physics in dwarf galaxy scales.

We present a detailed study of the infrared spectral energy distribution of the high-redshift radio galaxy MRC 1138-26 at z = 2.156, also known as the Spiderweb Galaxy. By combining photometry from Spitzer, Herschel, and LABOCA we fit the rest-frame 5–300 μm emission using a two-component, starburst, and active galactic nucleus (AGN) model. The total infrared (8–1000 μm) luminosity of this galaxy is (1.97  ±  0.28)  ×  10¹³ L_☉ with (1.17  ±  0.27) and (0.79  ±  0.09)  ×  10¹³ L_☉ due to the AGN and starburst components, respectively. The high derived AGN accretion rate of ∼20% Eddington and the measured star formation rate (SFR) of 1390  ±  150 M_☉ yr⁻¹ suggest that this massive system is in a special phase of rapid central black hole and host galaxy growth, likely caused by a gas-rich merger in a dense environment. The accretion rate is sufficient to power both the jets and the previously observed large outflow. The high SFR and strong outflow suggest that this galaxy could potentially exhaust its fuel for stellar growth in a few tens of Myr, although the likely merger of the radio galaxy with nearby satellites suggests that bursts of star formation may recur again on timescales of several hundreds of Myr. The age of the radio lobes implies the jet started after the current burst of star formation, and therefore we are possibly witnessing the transition from a merger-induced starburst phase to a radio-loud AGN phase. We also note tentative evidence for [C ii]158 μm emission. This paper marks the first results from the Herschel Galaxy Evolution Project (Project HeRGÉ), a systematic study of the evolutionary state of 71 high-redshift, 1 < z < 5.2, radio galaxies.

The flat-spectrum radio quasar 4C +21.35 (PKS 1222+216) displays prominent nuclear infrared emission from ≈1200 K dust. A 70–400 GeV flare with ≈10 minute variations during half an hour of observations was found by the MAGIC telescopes, and GeV variability was observed on sub-day timescales with the Large Area Telescope on Fermi. We examine 4C +21.35, assuming that it is a source of ultra-high energy cosmic rays (UHECRs). UHECR proton acceleration in the inner jet powers a neutral beam of neutrinos, neutrons, and γ-rays from pγ photopion production. The radiative efficiency and production spectra of neutrals formed through photohadronic processes with isotropic external target photons of the broad-line region (BLR) and torus are calculated. Secondary radiations made by this process have a beaming factor ∝δ⁵_D, where δ_D is the Doppler factor. The pair-production optical depth for γ-rays and the photopion efficiency for UHECR neutrons as they pass through external isotropic radiation fields are calculated. If target photons come from the BLR and dust torus, large Doppler factors, δ_D ≳ 100, are required to produce rapidly variable secondary radiation with isotropic luminosity ≳ 10⁴⁷ erg s⁻¹ at the pc scale. The γ-ray spectra from leptonic secondaries are calculated from cascades initiated by the UHECR neutron beam at the pc-scale region and fit to the flaring spectrum of 4C +21.35. Detection of ≳ 100 TeV neutrinos from 4C +21.35 or other very high energy γ-ray blazars with IceCube or KM3NeT would confirm this scenario.

We use the ultra-deep HUDF09 and the deep Early Release Science data from the HST WFC3/IR camera, along with the wide-area Spitzer/IRAC data from GOODS-S to derive spectral energy distributions (SEDs) of star-forming galaxies from the rest-frame UV to the optical over a wide luminosity range (M₁₅₀₀ ∼ −21 to M₁₅₀₀ ∼ −18) from z ∼ 7 to z ∼ 4. The sample contains ∼400 z ∼ 4, ∼120 z ∼ 5, ∼60 z ∼ 6, and 36 z ∼ 7 galaxies. Median stacking enables the first comprehensive SED study of very faint high-z galaxies at multiple redshifts (e.g., [3.6] = 27.4 ± 0.1 AB mag for the M₁₅₀₀ ∼ −18 sources at z ∼ 4). At z ∼ 4, we study the stacked SEDs over a range of 5 mag reaching down to ∼0.06L*_{z = 4}. We use all available SEDs and template fits to derive rest-frame UV-to-optical colors (U − V) at all redshifts and luminosities. We find that this color does not vary significantly with redshift at a fixed luminosity. The UV-to-optical color does show a weak trend with luminosity, becoming redder at higher luminosities. This is most likely due to dust. At z ≳ 5, we find blue [3.6]–[4.5] colors ∼ −0.3 mag that are most likely due to rest-frame optical emission lines contributing to the flux in the IRAC filter bandpasses. Such contributions would lower both ages and masses by ∼2 ×. The scatter in our derived SEDs remains large, but the results are most consistent with a lack of any evolution in the SEDs with redshift at a given luminosity. The uniformity of the SEDs suggests a self-similar mode of evolution over a timespan from 0.7 Gyr to 1.5 Gyr after the big bang that encompasses very substantial growth in the stellar mass density in the universe (from ∼4 × 10⁶ to ∼2 × 10⁷ M_☉ Mpc⁻³).

Advancements in infrared (IR) interferometry open up the possibility to spatially resolve active galactic nuclei (AGNs) on the parsec-scale level and study the circumnuclear dust distribution, commonly referred to as the "dust torus," that is held responsible for the type 1/type 2 dichotomy of AGNs. We used the mid-IR beam combiner MIDI together with the 8 m telescopes at the Very Large Telescope Interferometer to observe the nucleus of the Seyfert 2 galaxy NGC 424, achieving an almost complete coverage of the uv-plane accessible by the available telescope configurations. We detect extended mid-IR emission with a relatively baseline- and model-independent mid-IR half-light radius of (2.0 ± 0.2) pc × (1.5 ± 0.3) pc (averaged over the 8–13 μm wavelength range). The extended mid-IR source shows an increasing size with wavelength. These properties are in agreement with the idea of dust heated in thermal equilibrium with the AGN. The orientation of the major axis in position angle ∼ − 27° is closely aligned with the system axis as set by optical polarization observations. Torus models typically favor extension along the mid-plane at mid-IR wavelengths instead. Therefore, we conclude that the majority of the parsec-scale mid-IR emission (≳60%) in this type 2 AGN originates from optically thin dust in the polar region of the AGN, a scenario consistent with the near- to far-IR spectral energy distribution. We suggest that a radiatively driven dusty wind, possibly launched in a puffed-up region of the inner hot part of the torus, is responsible for the polar dust. In this picture, the torus dominates the near-IR emission up to about 5 μm, while the polar dust is the main contributor to the mid-IR flux. Our results of NGC 424 are consistent with recent observations of the AGN in the Circinus galaxy and resemble large-scale characteristics of other objects. If our results reflect a general property of the AGN population, the current paradigm for interpreting and modeling the IR emission of AGNs has to be revised.

In early 2008 October, the soft gamma repeater SGR J1550−5418 (1E 1547.0−5408, AX J155052−5418, PSR J1550−5418) became active, emitting a series of bursts which triggered the Fermi Gamma-ray Burst Monitor (GBM) after which a second especially intense activity period commenced in 2009 January and a third, less active period was detected in 2009 March–April. Here, we analyze the GBM data for all the bursts from the first and last active episodes. We performed temporal and spectral analysis for all events and found that their temporal characteristics are very similar to the ones of other SGR bursts, as well the ones reported for the bursts of the main episode (average burst durations ∼170 ms). In addition, we used our sample of bursts to quantify the systematic uncertainties of the GBM location algorithm for soft gamma-ray transients to ≲8°. Our spectral analysis indicates significant spectral evolution between the first and last set of events. Although the 2008 October events are best fitted with a single blackbody function, for the 2009 bursts an optically thin thermal bremsstrahlung is clearly preferred. We attribute this evolution to changes in the magnetic field topology of the source, possibly due to effects following the very energetic main bursting episode.

We report on a new Chandra exposure of PSR J1809−2332, the recently discovered pulsar powering the bright EGRET source 3EG J1809−2328. By registration of field X-ray sources in an archival exposure, we measure a significant proper motion for the pulsar point source over an ≈11 yr baseline. The shift of 0.30 ± 006 (at P.A. = 153.3 ± 18.4) supports an association with proposed supernova remnant (SNR) parent G7.5−1.7. Spectral analysis of diffuse emission in the region also supports the interpretation as a hard wind nebula trail pointing back toward the SNR.

The classic H ii region M17 is one of the best studied across the electromagnetic spectrum. We present sensitive, high angular resolution observations made with the Jansky Very Large Array at 4.96 and 8.46 GHz that reveal the presence of 38 compact radio sources, in addition to the well-known hypercompact cometary H ii region M17 UC1. For this last source, we find that its spectral index of the order of ∼1 is due to a gradient in opacity across its face. Of the 38 compact radio sources detected, 19 have stellar counterparts detected in the infrared, optical, or X-rays. Finally, we discuss the nature of the radio emission from the massive binary system CEN 1a and CEN 1b, concluding that both are most probably non-thermal emitters, although the first is strongly time variable and the second is steady.

The rotational spectrum of the higher-energy trans-conformational isomer of methyl formate has been assigned for the first time using several pulsed-jet Fourier transform microwave spectrometers in the 6–60 GHz frequency range. This species has also been sought toward the Sagittarius B2(N) molecular cloud using the publicly available PRIMOS survey from the Green Bank Telescope. We detect seven absorption features in the survey that coincide with laboratory transitions of trans-methyl formate, from which we derive a column density of 3.1 (+2.6, −1.2) × 10¹³ cm⁻² and a rotational temperature of 7.6 ± 1.5 K. This excitation temperature is significantly lower than that of the more stable cis conformer in the same source but is consistent with that of other complex molecular species recently detected in Sgr B2(N). The difference in the rotational temperatures of the two conformers suggests that they have different spatial distributions in this source. As the abundance of trans-methyl formate is far higher than would be expected if the cis and trans conformers are in thermodynamic equilibrium, processes that could preferentially form trans-methyl formate in this region are discussed. We also discuss measurements that could be performed to make this detection more certain. This manuscript demonstrates how publicly available broadband radio astronomical surveys of chemically rich molecular clouds can be used in conjunction with laboratory rotational spectroscopy to search for new molecules in the interstellar medium.

The present observational understanding of the evolution of the mass accretion rates ($\dot{M}_{\rm acc}$) in pre-main-sequence stars is limited by the lack of accurate measurements of $\dot{M}_{\rm acc}$ over homogeneous and large statistical samples of young stars. Such observational effort is needed to properly constrain the theory of star formation and disk evolution. Based on Hubble Space Telescope/WFPC2 observations, we present a study of $\dot{M}_{\rm acc}$ for a sample of ∼700 sources in the Orion Nebula Cluster, ranging from the hydrogen-burning limit to M_* ∼ 2 M_☉. We derive $\dot{M}_{\rm acc}$ from both the U-band excess and the Hα luminosity (L_Hα), after determining empirically both the shape of the typical accretion spectrum across the Balmer jump and the relation between the accretion luminosity (L_acc) and L_Hα, which is L_acc/L_☉ = (1.31 ± 0.03) · L_Hα/L_☉ + (2.63 ± 0.13). Given our large statistical sample, we are able to accurately investigate relations between $\dot{M}_{\rm acc}$ and the parameters of the central star such as mass and age. We clearly find $\dot{M}_{\rm acc}$ to increase with stellar mass and decrease over evolutionary time, but we also find strong evidence that the decay of $\dot{M}_{\rm acc}$ with stellar age occurs over longer timescales for more massive PMS stars. Our best-fit relation between these parameters is given by log ($\dot{M}_{\rm acc}$/M_☉ yr) = (−5.12 ± 0.86) − (0.46 ± 0.13) ·  log (t/yr) − (5.75 ± 1.47) ·  log (M_*/M_☉) + (1.17 ± 0.23) ·  log (t/yr)  ·  log (M_*/M_☉). These results also suggest that the similarity solution model could be revised for sources with M_* ≳ 0.5 M_☉. Finally, we do not find a clear trend indicating environmental effects on the accretion properties of the sources.

We investigate the origin and fate of the recently discovered gas cloud G2 close to the Galactic center. Our hydrodynamical simulations focusing on the dynamical evolution of the cloud in combination with currently available observations favor two scenarios: a Compact Cloud which started around the year 1995 and a Spherical Shell of gas, with an apocenter distance within the disk(s) of young stars and a radius of a few times the size of the Compact Cloud. The former is able to explain the detected signal of G2 in the position–velocity (PV) diagram of the Brγ emission of the year 2008.5 and 2011.5 data. The latter can account for both G2's signal as well as the fainter extended tail-like structure G2t seen at larger distances from the black hole and smaller velocities. In contrast, gas stripped from a compact cloud by hydrodynamical interactions is not able to explain the location of the detected G2t emission in the observed PV diagrams. This favors the Spherical Shell Scenario and might be a severe problem for the Compact Cloud as well as the so-called Compact Source Scenario. From these first idealized simulations, we expect a roughly constant feeding of the supermassive black hole through a nozzle-like structure over a long period, starting shortly after the closest approach in 2013.51 for the Compact Cloud. If the matter accretes in the hot accretion mode, we do not expect a significant boost of the current activity of Sgr A* for the Compact Cloud model, but a boost of the average infrared and X-ray luminosity by roughly a factor of 80 for the Spherical Shell Scenario with order of magnitude variations on a timescale of a few months. Assuming that a part of the gas is accreted in cold disk mode, even higher boost factors can be reached. The near-future evolution of the cloud will be a sensitive probe of the conditions of the gas distribution in the milli-parsec environment of the massive black hole in the Galactic center.

We present the results of a comprehensive analysis of the structure and kinematics of six Galactic globular clusters. By comparing the results of the most extensive photometric and kinematical surveys available to date with suitable dynamical models, we determine the stellar and dynamical masses of these stellar systems taking into account the effect of mass segregation, anisotropy, and unresolved binaries. We show that the stellar masses of these clusters are on average smaller than those predicted by canonical integrated stellar evolution models because of the shallower slopes of their mass functions. The derived stellar masses are found to be also systematically smaller than the dynamical masses by ∼40%, although the presence of systematics affecting our estimates cannot be excluded. If confirmed, this evidence can be linked to an increased fraction of retained dark remnants or to the presence of a modest amount of dark matter.

We present 230 GHz Submillimeter Array continuum and molecular line observations of the newly discovered FU Orionis candidate HBC722. We report the detection of seven 1.3 mm continuum sources in the vicinity of HBC722, none of which corresponds to HBC722 itself. We compile infrared and submillimeter continuum photometry of each source from previous studies and conclude that three are Class 0 embedded protostars, one is a Class I embedded protostar, one is a Class I/II transition object, and two are either starless cores or very young, very low luminosity protostars or first hydrostatic cores. We detect a northwest–southeast outflow, consistent with the previous detection of such an outflow in low-resolution, single-dish observations, and note that its axis may be precessing. We show that this outflow is centered on and driven by one of the nearby Class 0 sources rather than HBC722, and find no conclusive evidence that HBC722 itself is driving an outflow. The non-detection of HBC722 in the 1.3 mm continuum observations suggests an upper limit of 0.02 M_☉ for the mass of the circumstellar disk. This limit is consistent with typical T Tauri disks and with a disk that provides sufficient mass to power the burst.

We used the Palomar Testbed Interferometer (PTI) to resolve 2.2 μm emission from the classical nova V458 Vul 2007 over the course of several days following its discovery on 2007 August 8.54 UT. We also obtained K-band photometric data and spectra of the nova during the early days of the outburst. We also used photometric measurements from the AAVSO database. This is a unique data set offering a three-technique approach: high-resolution imaging, spectroscopy, and photometry. Our analysis shows that the nova ejecta can be modeled as an inclined disk at low inclination, i.e., low ellipticity which is consistent with the nova being in the fireball phase at which the outflowing gas is optically thick, confirmed by the presence of strong P-Cygni Balmer lines in the spectra. The expansion velocity is ≈1700 km s⁻¹, derived from the Hα line. By combining the nova's angular expansion rate measured by PTI with the expansion rate measured from spectroscopy, the inferred distance to the nova is 9.9–11.4 kpc. We also used the K-band fluxes and the derived size of the emission to estimate the total mass ejected from the nova ≈4 × 10⁻⁴ M_☉. The quick transition of the nova from Fe ii to He/N class makes V458 Vul 2007 a hybrid nova.

Kinetic plasma theory is used to generate synthetic spacecraft data to analyze and interpret the compressible fluctuations in the inertial range of solar wind turbulence. The kinetic counterparts of the three familiar linear MHD wave modes—the fast, Alfvén, and slow waves—are identified, and the properties of the density–parallel magnetic field correlation for these kinetic wave modes are presented. The construction of synthetic spacecraft data, based on the quasi-linear premise—that some characteristics of magnetized plasma turbulence can be usefully modeled as a collection of randomly phased, linear wave modes—is described in detail. Theoretical predictions of the density–parallel magnetic field correlation based on MHD and Vlasov–Maxwell linear eigenfunctions are presented and compared to the observational determination of this correlation based on 10 years of Wind spacecraft data. It is demonstrated that MHD theory is inadequate to describe the compressible turbulent fluctuations and that the observed density–parallel magnetic field correlation is consistent with a statistically negligible kinetic fast wave energy contribution for the large sample used in this study. A model of the solar wind inertial range fluctuations is proposed composed of a mixture of a critically balanced distribution of incompressible Alfvénic fluctuations and a critically balanced or more anisotropic than critical balance distribution of compressible slow wave fluctuations. These results imply that there is little or no transfer of large-scale turbulent energy through the inertial range down to whistler waves at small scales.

It is suggested in observations of supernova remnants that a number of large- and small-scale structures form at various points in the explosion. Multi-dimensional modeling of core-collapse supernovae has been undertaken since SN1987A, and both simulations and observations suggest/show that Rayleigh–Taylor (RT) instabilities during the explosion is a main driver of the formation of structure in the remnants. We present a case study of structure formation in three dimensions in a 15 M_☉ supernova for different parameters. We investigate the effect of moderate asymmetries and different resolutions of the formation and morphology of the RT unstable region, and take first steps toward determining typical physical quantities (size, composition) of arising clumps. We find that in this progenitor the major RT unstable region develops at the He/OC interface for all cases considered. The RT instabilities result in clumps that are overdense by one to two orders of magnitude with respect to the ambient gas, have size scales on the level of a few percent of the remnant diameter, and are not diffused after the first ∼30 yr of the remnant evolution, in the absence of a surrounding medium.

From the first two seasons of the Palomar Transient Factory, we identify three peculiar transients (PTF 09dav, PTF 10iuv, and PTF 11bij) with five distinguishing characteristics: peak luminosity in the gap between novae and supernovae (M_R ≈ −15.5 to −16.5 mag), rapid photometric evolution (t_rise ≈ 12–15 days), large photospheric velocities (≈6000–11,000 km s⁻¹), early spectroscopic evolution into nebular phase (≈1–3 months), and peculiar nebular spectra dominated by calcium. We also culled the extensive decade-long Lick Observatory Supernova Search database and identified an additional member of this group, SN 2007ke. Our choice of photometric and spectroscopic properties was motivated by SN 2005E (Perets et al.). To our surprise, as in the case of SN 2005E, all four members of this group are also clearly offset from the bulk of their host galaxy. Given the well-sampled early- and late-time light curves, we derive ejecta masses in the range of 0.4–0.7 M_☉. Spectroscopically, we find that there may be a diversity in the photospheric phase, but the commonality is in the unusual nebular spectra. Our extensive follow-up observations rule out standard thermonuclear and standard core-collapse explosions for this class of "calcium-rich gap" transients. If the progenitor is a white dwarf, we are likely seeing a detonation of the white dwarf core and perhaps even shock-front interaction with a previously ejected nova shell. If the progenitor is a massive star, a nonstandard channel specific to a low-metallicity environment needs to be invoked (e.g., ejecta fallback leading to black hole formation). Detection (or the lack thereof) of a faint underlying host (dwarf galaxy and cluster) will provide a crucial and decisive diagnostic to choose between these alternatives.

We report the spectral and temporal variability properties of 18 candidate transient (TC) and potential transient (PTC) sources detected in deep multi-epoch Chandra observation of the nearby elliptical galaxies, NGC 3379, NGC 4278, and NGC 4697. Only one source can be identified with a background counterpart, leaving 17 TCs + PTCs in the galaxies. Of these, 14 are in the galaxy field, supporting the theoretical picture that the majority of field X-ray binaries (XRBs) will exhibit transient accretion for >75% of their lifetime. Three sources are coincident with globular clusters, including two high-luminosity candidate black hole (BH) XRBs, with L_X = 5.4 × 10³⁸ erg s⁻¹and L_X = 2.8 × 10³⁹ erg s⁻¹, respectively. The spectra, luminosities, and temporal behavior of these 17 sources suggest that the transient population is heterogeneous, including neutron star (NS) and BH XRBs in both normal and high-rate accretion modes, and super soft sources containing white dwarf binaries. Our TC and PTC detections are noticeably fewer than the number expected from the population synthesis (PS) models of Fragos et al., tailored to our new Chandra pointings of NGC 4278. We attribute this discrepancy to the PS assumption that the transient population is composed of NS XRBs, as well as differences between the statistical analysis and error estimates used in the model and our observations.

We have modeled the inner surface brightness profiles of 39 alleged "core" galaxies with the core-Sérsic model, and provide new physical parameters for the largest ever sample of "core" galaxies fit with this model. When present, additional nuclear components were simultaneously modeled and the typical root-mean-square scatter of the fits (out to ∼10'') is 0.02 mag arcsec⁻². Model-independent estimates of each core's break radius are shown to agree with those from the core-Sérsic model, and a comparison with the Nuker model is provided. We found an absence of cores in what amounts to 18% of the sample, which are reclassified here as Sérsic galaxies with low values of n (≲ 4) and thus shallow inner profile slopes. In general, galaxies with n < 3 and σ < 183 km s⁻¹ do not have depleted cores. We derive updated relations between core-Sérsic break radii, their associated surface brightness, bulge luminosity, central velocity dispersion, and predicted black hole mass for galaxies with depleted cores. With the possible exception of NGC 584, we confirm that the inner negative logarithmic profile slopes γ are ≲0.3 for the "core" galaxies, and 0 > γ > −0.1 for six of these. Finally, the central stellar mass deficits are found to have values typically within a factor of four of the expected central black hole mass.

Recent detections of the starburst galaxies M82 and NGC 253 by gamma-ray telescopes suggest that galaxies rapidly forming massive stars are more luminous at gamma-ray energies compared to their quiescent relatives. Building upon those results, we examine a sample of 69 dwarf, spiral, and luminous and ultraluminous infrared galaxies at photon energies 0.1–100 GeV using 3 years of data collected by the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (Fermi). Measured fluxes from significantly detected sources and flux upper limits for the remaining galaxies are used to explore the physics of cosmic rays in galaxies. We find further evidence for quasi-linear scaling relations between gamma-ray luminosity and both radio continuum luminosity and total infrared luminosity which apply both to quiescent galaxies of the Local Group and low-redshift starburst galaxies (conservative P-values ≲ 0.05 accounting for statistical and systematic uncertainties). The normalizations of these scaling relations correspond to luminosity ratios of log (L_{0.1–100 GeV}/L_1.4 GHz) = 1.7 ± 0.1_{(statistical)} ± 0.2_(dispersion) and log (L_{0.1–100 GeV}/L_{8–1000 μm}) = −4.3 ± 0.1_{(statistical)} ± 0.2_(dispersion) for a galaxy with a star formation rate of 1 M_☉ yr⁻¹, assuming a Chabrier initial mass function. Using the relationship between infrared luminosity and gamma-ray luminosity, the collective intensity of unresolved star-forming galaxies at redshifts 0 < z < 2.5 above 0.1 GeV is estimated to be 0.4–2.4 × 10⁻⁶ ph cm⁻² s⁻¹ sr⁻¹ (4%–23% of the intensity of the isotropic diffuse component measured with the LAT). We anticipate that ∼10 galaxies could be detected by their cosmic-ray-induced gamma-ray emission during a 10 year Fermi mission.

Using infrared imaging from the Herschel Space Observatory, observed as part of the Very Nearby Galaxies Survey, we investigate the spatially resolved dust properties of the interacting Whirlpool galaxy system (NGC 5194 and NGC 5195), on physical scales of ∼1 kpc. Spectral energy distribution modeling of the new infrared images in combination with archival optical and near- through mid-infrared images confirms that both galaxies underwent a burst of star formation ∼370–480 Myr ago and provides spatially resolved maps of the stellar and dust mass surface densities. The resulting average dust-to-stellar mass ratios are comparable to other spiral and spheroidal galaxies studied with Herschel, with NGC 5194 at log (M_dust/M_⋆) = −2.5 ± 0.2 and NGC 5195 at log (M_dust/M_⋆) = −3.5 ± 0.3. The dust-to-stellar mass ratio is constant across NGC 5194 suggesting the stellar and dust components are coupled. In contrast, the mass ratio increases with radius in NGC 5195 with decreasing stellar mass density. Archival mass surface density maps of the neutral and molecular hydrogen gas are also folded into our analysis, revealing a fairly constant gas-to-dust mass ratio, 94 ± 17 across the system. Somewhat surprisingly, we find the dust in NGC 5195 is heated by a strong interstellar radiation field (ISRF), over 20 times that of the ISRF in the Milky Way, resulting in relatively high characteristic dust temperatures (∼30 K). This post-starburst galaxy contains a substantial amount of low-density molecular gas and displays a gas-to-dust ratio (73 ± 35) similar to spiral galaxies. It is unclear why the dust in NGC 5195 is heated to such high temperatures as there is no star formation in the galaxy and its active galactic nucleus is 5–10 times less luminous than the one in NGC 5194, which exhibits only a modest enhancement in the amplitude of its ISRF.

The Elliptical Isolated X-ray (ElIXr) Galaxy Survey is a volume-limited (<110 Mpc) study of optically selected, isolated, L_* elliptical galaxies to provide an X-ray census of galaxy-scale (virial mass, M_vir ≲ 10¹³ M_☉) objects and identify candidates for detailed hydrostatic mass modeling. In this paper, we present a Chandra and XMM study of one such candidate, NGC 1521, and constrain its distribution of dark and baryonic matter. We find a morphologically relaxed hot gas halo, extending almost to R₅₀₀, that is well described by hydrostatic models similar to the benchmark, baryonically closed, Milky Way mass elliptical galaxy NGC 720. We obtain good constraints on the enclosed gravitating mass (M₅₀₀ = [3.8 ± 1.0] × 10¹² M_☉, slightly higher than NGC 720) and baryon fraction (f_{b, 500} = 0.13 ± 0.03). We confirm at 8.2σ the presence of a dark matter (DM) halo consistent with ΛCDM. Assuming a Navarro–Frenk–White DM profile, our self-consistent, physical model enables meaningful constraints beyond R₅₀₀, revealing that most of the baryons are in the hot gas. Within the virial radius, f_b is consistent with the cosmic mean, suggesting that the predicted massive, quasi-hydrostatic gas halos may be more common than previously thought. We confirm that the DM and stars conspire to produce an approximately power-law total mass profile (ρ_tot∝r^−α) that follows the recently discovered scaling relation between α and optical effective radius. Our conclusions are insensitive to modest, observationally motivated, deviations from hydrostatic equilibrium. Finally, after correcting for the enclosed gas fraction, the entropy profile is close to the self-similar prediction of gravitational structure formation simulations, as observed in massive galaxy clusters.

We have conducted a systematic search of low-mass black holes (BHs) in active galactic nuclei (AGNs) with broad Hα emission lines, aiming at building a homogeneous sample that is more complete than previous ones for fainter, less highly accreting sources. For this purpose, we developed a set of elaborate, automated selection procedures and applied it uniformly to the Fourth Data Release of the Sloan Digital Sky Survey. Special attention is given to AGN–galaxy spectral decomposition and emission-line deblending. We define a sample of 309 type 1 AGNs with BH masses in the range 8 × 10⁴–2 × 10⁶ M_☉ (with a median of 1.2 × 10⁶ M_☉), using the virial mass estimator based on the broad Hα line. About half of our sample of low-mass BHs differs from that of Greene & Ho, with 61 of them discovered here for the first time. Our new sample picks up more AGNs with low accretion rates: the Eddington ratios of the present sample range from ≲ 0.01 to ∼1, with 30% below 0.1. This suggests that a significant fraction of low-mass BHs in the local universe are accreting at low rates. The host galaxies of the low-mass BHs have luminosities similar to those of L* field galaxies, optical colors of Sbc spirals, and stellar spectral features consistent with a continuous star formation history with a mean stellar age of less than 1 Gyr.

We present spectroscopic observations in the rest-frame optical and near- to mid-infrared wavelengths of four gravitationally lensed infrared (IR) luminous star-forming galaxies at redshift 1 <z < 3 from the LUCIFER instrument on the Large Binocular Telescope and the Infrared Spectrograph on Spitzer. The sample was selected to represent pure, actively star-forming systems, absent of active galactic nuclei. The large lensing magnifications result in high signal-to-noise spectra that can probe faint IR recombination lines, including Paα and Brα at high redshifts. The sample was augmented by three lensed galaxies with similar suites of unpublished data and observations from the literature, resulting in the final sample of seven galaxies. We use the IR recombination lines in conjunction with Hα observations to probe the extinction, A_v, of these systems, as well as testing star formation rate (SFR) indicators against the SFR measured by fitting spectral energy distributions to far-IR photometry. Our galaxies occupy a range of A_v from ∼0 to 5.9 mag, larger than previously known for a similar range of IR luminosities at these redshifts. Thus, estimates of SFR even at z ∼ 2 must take careful count of extinction in the most IR luminous galaxies. We also measure extinction by comparing SFR estimates from optical emission lines with those from far-IR measurements. The comparison of results from these two independent methods indicates a large variety of dust distribution scenarios at 1 < z < 3. Without correcting for dust extinction, the Hα SFR indicator underestimates the SFR; the size of the necessary correction depends on the IR luminosity and dust distribution scenario. Individual SFR estimates based on the 6.2 μm polycyclic aromatic hydrocarbon emission line luminosity do not show a systematic discrepancy with extinction, although a considerable, ∼ 0.2 dex, scatter is observed.

We investigate the high-redshift quasar luminosity function (QLF) down to an apparent magnitude of I_AB = 25 in the Cosmic Evolution Survey (COSMOS). Careful analysis of the extensive COSMOS photometry and imaging data allows us to identify and remove stellar and low-redshift contaminants, enabling a selection that is nearly complete for type-1 quasars at the redshifts of interest. We find 155 likely quasars at z > 3.1, 39 of which have prior spectroscopic confirmation. We present our sample in detail and use these confirmed and likely quasars to compute the rest-frame UV QLF in the redshift bins 3.1 < z < 3.5 and 3.5 < z < 5. The space density of faint quasars decreases by roughly a factor of four from z ∼ 3.2 to z ∼ 4, with faint-end slopes of β ∼ −1.7 at both redshifts. The decline in space density of faint optical quasars at z > 3 is similar to what has been found for more luminous optical and X-ray quasars. We compare the rest-frame UV luminosity functions found here with the X-ray luminosity function at z > 3, and find that they evolve similarly between z ∼ 3.2 and z ∼ 4; however, the different normalizations imply that roughly 75% of X-ray bright active galactic nuclei (AGNs) at z ∼ 3–4 are optically obscured. This fraction is higher than found at lower redshift and may imply that the obscured, type-2 fraction continues to increase with redshift at least to z ∼ 4. Finally, the implications of the results derived here for the contribution of quasars to cosmic reionization are discussed.

Active galactic nuclei with misaligned jets have been recently established as a class of high-energy gamma-ray sources. M87, a nearby representative of this class, shows fast TeV variability on timescales less than one day. We present calculations performed in the framework of the scenario in which gamma-ray flares in non-blazar active galactic nuclei are produced by a red giant or a gas cloud interacting with the jet. We show that both the light curve and energy spectrum of the spectacular 2010 April flare can be reproduced by this model, assuming that a relatively massive cloud of ∼10²⁹ g penetrates into the jet at few tens of Schwarzschild radii from the supermassive black hole.

Results are presented for [C ii] 158 μm line fluxes observed with the Herschel PACS instrument in 112 sources with both starburst and active galactic nucleus (AGN) classifications, of which 102 sources have confident detections. Results are compared with mid-infrared spectra from the Spitzer Infrared Spectrometer and with L_ir from IRAS fluxes; AGN/starburst classifications are determined from equivalent width of the 6.2 μm polycyclic aromatic hydrocarbon (PAH) feature. It is found that the [C ii] line flux correlates closely with the flux of the 11.3 μm PAH feature independent of AGN/starburst classification, log [f([C ii] 158 μm)/f(11.3 μm PAH)] = −0.22 ± 0.25. It is concluded that the [C ii] line flux measures the photodissociation region associated with starbursts in the same fashion as the PAH feature. A calibration of star formation rate (SFR) for the starburst component in any source having [C ii] is derived comparing [C ii] luminosity L([C ii]) to L_ir with the result that log SFR = log L([C ii)]) − 7.08 ± 0.3, for SFR in M_☉ yr⁻¹ and L([C ii]) in L_☉. The decreasing ratio of L([C ii]) to L_ir in more luminous sources (the "[C ii] deficit") is shown to be a consequence of the dominant contribution to L_ir arising from a luminous AGN component because the sources with the largest L_ir and smallest L([C ii])/L_ir are AGNs.

We present deep Giant Metrewave Radio Telescope (GMRT) radio observations at 240, 330, and 610 MHz of the complex radio source at the center of the NGC 1407 galaxy group. Previous GMRT observations at 240 MHz revealed faint, diffuse emission enclosing the central twin-jet radio galaxy. This has been interpreted as an indication of two possible radio outbursts occurring at different times. Both the inner double and diffuse components are detected in the new GMRT images at high levels of significance. Combining the GMRT observations with archival Very Large Array data at 1.4 and 4.9 GHz, we derive the total spectrum of both components. The inner double has a spectral index α = 0.7, typical for active, extended radio galaxies, whereas the spectrum of the large-scale emission is very steep, with α = 1.8 between 240 MHz and 1.4 GHz. The radiative age of the large-scale component is very long, ∼300 Myr, compared to ∼30 Myr estimated for the central double, confirming that the diffuse component was generated during a former cycle of activity of the central galaxy. The current activity have so far released an energy which is nearly one order of magnitude lower than that associated with the former outburst. The group x-ray emission in the Chandra and XMM-Newton images and extended radio emission show a similar swept-back morphology. We speculate that the two structures are both affected by the motion of the group core, perhaps due to the core sloshing in response to a recent encounter with the nearby elliptical galaxy NGC 1400.

We report the discovery by the Wide-field Infrared Survey Explorer (WISE) of the z = 2.452 source WISE J181417.29+341224.9, the first hyperluminous source found in the WISE survey. WISE 1814+3412 is also the prototype for an all-sky sample of ∼1000 extremely luminous "W1W2-dropouts" (sources faint or undetected by WISE at 3.4 and 4.6 μm and well detected at 12 or 22 μm). The WISE data and a 350 μm detection give a minimum bolometric luminosity of 3.7 × 10¹³ L_☉, with ∼10¹⁴ L_☉ plausible. Follow-up images reveal four nearby sources: a QSO and two Lyman break galaxies (LBGs) at z = 2.45, and an M dwarf star. The brighter LBG dominates the bolometric emission. Gravitational lensing is unlikely given the source locations and their different spectra and colors. The dominant LBG spectrum indicates a star formation rate ∼300 M_☉ yr⁻¹, accounting for ≲ 10% of the bolometric luminosity. Strong 22 μm emission relative to 350 μm implies that warm dust contributes significantly to the luminosity, while cooler dust normally associated with starbursts is constrained by an upper limit at 1.1 mm. Radio emission is ∼10 times above the far-infrared/radio correlation, indicating an active galactic nucleus (AGN) is present. An obscured AGN combined with starburst and evolved stellar components can account for the observations. If the black hole mass follows the local M_BH–bulge mass relation, the implied Eddington ratio is ≳ 4. WISE 1814+3412 may be a heavily obscured object where the peak AGN activity occurred prior to the peak era of star formation.

We present a detailed study of the x-ray, optical, and radio emission from the jet, lobes, and core of the quasar PKS 2101−490 as revealed by new Chandra, Hubble Space Telescope (HST), and ATCA images. We extract the radio to x-ray spectral energy distributions from seven regions of the 13'' jet, and model the jet x-ray emission in terms of Doppler beamed inverse Compton scattering of the cosmic microwave background (IC/CMB) for a jet in a state of equipartition between particle and magnetic field energy densities. This model implies that the jet remains highly relativistic hundreds of kiloparsecs from the nucleus, with a bulk Lorentz factor Γ ∼ 6 and magnetic field of the order of 30 μG. We detect an apparent radiative cooling break in the synchrotron spectrum of one of the jet knots, and are able to interpret this in terms of a standard one-zone continuous injection model, based on jet parameters derived from the IC/CMB model. However, we note apparent substructure in the bright optical knot in one of the HST bands. We confront the IC/CMB model with independent estimates of the jet power, and find that the IC/CMB model jet power is consistent with the independent estimates, provided that the minimum electron Lorentz factor γ_min ≳ 50, and the knots are significantly longer than the jet width, as implied by de-projection of the observed knot lengths.

We analyze two regions of the quiet Sun (35.6 × 35.6 Mm²) observed at high spatial resolution (≲100 km) in polarized light by the IMaX spectropolarimeter on board the SUNRISE balloon. We identify 497 small-scale (∼400 km) magnetic loops, appearing at an effective rate of 0.25 loop h⁻¹ arcsec⁻²; further, we argue that this number and rate are underestimated by ∼30%. However, we find that these small dipoles do not appear uniformly on the solar surface: their spatial distribution is rather filamentary and clumpy, creating dead calm areas, characterized by a very low magnetic signal and a lack of organized loop-like structures at the detection level of our instruments, which cannot be explained as just statistical fluctuations of a Poisson spatial process. We argue that this is an intrinsic characteristic of the mechanism that generates the magnetic fields in the very quiet Sun. The spatio-temporal coherences and the clumpy structure of the phenomenon suggest a recurrent, intermittent mechanism for the generation of magnetic fields in the quietest areas of the Sun.

Confrontations of spectroscopic observations with local thermodynamic equilibrium (LTE) spectral syntheses in a three-dimensional (3D) hydrodynamical model of the solar photosphere led to a downward revision of the photospheric and meteoritic silicon abundances. Here we derive the photospheric silicon abundance taking into account non-LTE (NLTE) effects in the same 3D model. We show that the above-mentioned downward revision of the silicon abundance is caused by using the LTE approximation in the context of 3D modeling, an experimental scale of oscillator strengths, and a small number of Si i lines. We demonstrate that no revision of the solar silicon abundance is required if NLTE effects are taken into account and one uses a "solar" oscillator strength scale and an extended list of Si i lines. The NLTE abundance value we find by fitting the equivalent widths of 65 Si i lines is A^NLTE_Si = 7.549 ± 0.016. This value agrees well with the silicon abundance that had been recommended earlier by Grevesse & Sauval and Lodders for the solar photosphere and CI chondrite meteorites.

We present observational data for two main components (S255IR and S255N) of the S255 high mass star-forming region in continuum and molecular lines obtained at 1.3 mm and 1.1 mm with the Submillimeter Array (SMA), at 1.3 cm with the Very Large Array, and at 23 and 50 cm with the Giant Metrewave Radio Telescope. The angular resolution was from ∼2'' to ∼5'' for all instruments. With the SMA we detected a total of about 50 spectral lines of 20 different molecules (including isotopologues). About half of the lines and half of the species (in particular N₂H⁺, SiO, C³⁴S, DCN, DNC, DCO⁺, HC₃N, H₂CO, H₂CS, SO₂) have not been previously reported in S255IR and partly in S255N at high angular resolution. Our data reveal several new clumps in the S255IR and S255N areas through their millimeter wave continuum emission. Masses of these clumps are estimated at a few solar masses. The line widths greatly exceed expected thermal widths. These clumps have practically no association with NIR or radio continuum sources, implying a very early stage of evolution. At the same time, our SiO data indicate the presence of high-velocity outflows related to some of these clumps. In some cases, strong molecular emission at velocities of the quiescent gas has no detectable counterpart in the continuum. We discuss the main features of the distribution of NH₃, N₂H⁺, and deuterated molecules. We estimate properties of decimeter wave radio continuum sources and their relationship with the molecular material.

We present SMA and CARMA continuum and spectral line observations of five dense cores located in the Perseus and Ophiuchus molecular clouds whose masses exceed their thermal Jeans masses. Three of these cores have previously been identified as being starless and two have been classified as being possibly protostellar. We find that one core is certainly protostellar. The other four cores, however, are starless and undetected in both C¹⁸O and 1.3 mm continuum emission. These four starless cores have flat density profiles out to at least ∼0.006 pc, which is typical for starless cores in general. Density profiles predicted by some collapse models, especially in the early stages of infall, are consistent with our observations. Archival data reveal that these starless cores have significant non-thermal support against collapse, although they may still be unstable.

We derive the distribution of flux density of a compact source exhibiting strong diffractive scintillation. Our treatment accounts for arbitrary spectral averaging, spatially extended source emission, and the possibility of intrinsic variability within the averaging time, as is typical for pulsars. We also derive the modulation index and present a technique for estimating the self-noise of the distribution, which can be used to identify amplitude variations on timescales shorter than the spectral accumulation time. Our results enable a direct comparison with ultra-high-resolution observations of pulsars, particularly single-pulse studies with Nyquist-limited resolution, and can be used to identify the spatial emission structure of individual pulses at a small fraction of the diffractive scale.

We have used deep V and R images acquired at the ESO Very Large Telescope to identify the optical companion to the binary PSR J0610−2100, one of the black-widow millisecond pulsars recently detected by the Fermi Gamma-ray Space Telescope in the Galactic plane. We found a faint star (V ∼ 26.7) nearly coincident (δr ∼ 028) with the pulsar nominal position. This star is visible only in half of the available images, while it disappears in the deepest ones (those acquired under the best-seeing conditions), thus indicating that it is variable. Although our observations do not sample the entire orbital period (P = 0.28 days) of the pulsar, we found that the optical modulation of the variable star nicely correlates with the pulsar orbital period and describes a well-defined peak (R ∼ 25.6) at Φ = 0.75, suggesting a modulation due to the pulsar heating. We tentatively conclude that the companion to PSR J0610−2100 is a heavily ablated very low mass star (≈0.02 M_☉) that completely filled its Roche lobe.

Many astrophysical phenomena (such as the slow rotation of neutron stars or the rigid rotation of the solar core) can be explained by the action of the Tayler instability of toroidal magnetic fields in the radiative zones of stars. In order to place the theory of this instability on a safe fundament, it has been realized in a laboratory experiment measuring the critical field strength, the growth rates, as well as the shape of the supercritical modes. A strong electrical current flows through a liquid metal confined in a resting columnar container with an insulating outer cylinder. As the very small magnetic Prandtl number of the gallium–indium–tin alloy does not influence the critical Hartmann number of the field amplitudes, the electric currents for marginal instability can also be computed with direct numerical simulations. The results of this theoretical concept are confirmed by the experiment. Also the predicted growth rates on the order of minutes for the nonaxisymmetric perturbations are certified by the measurements. That they do not directly depend on the size of the experiment is shown as a consequence of the weakness of the applied fields and the absence of rotation.