Table of contents

Observations of the cyclotron resonance scattering feature in the X-ray spectrum of GX 301–2 suggest that the surface field of the neutron star is B_CRSF ∼ 4 × 10¹² G. The same value has been derived in modeling the rapid spin-up episodes in terms of the Keplerian disk accretion scenario. However, the spin-down rate observed during the spin-down trends significantly exceeds the value expected in currently used spin-evolution scenarios. This indicates that either the surface field of the star exceeds 50 B_CRSF or a currently used accretion scenario is incomplete. We show that the above discrepancy can be avoided if the accreting material is magnetized. The magnetic pressure in the accretion flow increases more rapidly than its ram pressure and, under certain conditions, significantly affects the accretion picture. The spin-down torque applied to the neutron star in this case is larger than that evaluated within a non-magnetized accretion scenario. We find that the observed spin evolution of the pulsar can be explained in terms of the magnetically controlled accretion flow scenario provided the surface field of the neutron star is ∼B_CRSF.

We report on Chandra X-ray Observatory (Chandra) High Energy Transmission Grating spectra of the dipping low-mass X-ray binary 1A 1744−361 during its 2008 July outburst. We find that its persistent emission is well modeled by a blackbody (kT ∼ 1.0 keV) plus power law (Γ ∼ 1.7) with an absorption edge. In the residuals of the combined spectrum, we find a significant absorption line at 6.961 ± 0.002 keV, consistent with the Fe xxvi (hydrogen-like Fe) 2–1 transition. We place an upper limit on the velocity of a redshifted flow of v < 221 km s⁻¹. We find an equivalent width for the line of 27⁺²_{− 3} eV, from which we determine a column density of (7 ± 1) × 10¹⁷ cm⁻² via a curve-of-growth analysis. Using XSTAR simulations, we place a lower limit on the ionization parameter of >10^3.6 erg cm s⁻¹. We discuss what implications the feature has on the system and its geometry. We also present Rossi X-ray Timing Explorer data accumulated during this latest outburst and, via an updated color–color diagram, clearly show that 1A 1744−361 is an "atoll" source.

Results are presented for XMM-Newton observations of five hard X-ray sources discovered by INTEGRAL in the direction of the Scutum Arm. Each source received ≳20 ks of effective exposure time. We provide refined X-ray positions for all five targets enabling us to pinpoint the most likely counterpart in optical/infrared archives. Spectral and timing information (much of which is provided for the first time) allow us to give a firm classification for IGR J18462−0223 and to offer tentative classifications for the others. For IGR J18462−0223, we discovered a coherent pulsation period of 997 ± 1 s, which we attribute to the spin of a neutron star in a highly obscured (N_H =2 × 10²³ cm⁻²) high-mass X-ray binary (HMXB). This makes IGR J18462−0223 the seventh supergiant fast X-ray transient candidate with a confirmed pulsation period. IGR J18457+0244 is a highly absorbed (N_H =8 × 10²³ cm⁻²) source in which the possible detection of an iron line suggests an active galactic nucleus (AGN) of type Sey-2 situated at z = 0.07(1). A periodic signal at 4.4 ks could be a quasi-periodic oscillation which would make IGR J18457+0244 one of a handful of AGNs in which such features have been claimed, but a slowly rotating neutron star in an HMXB cannot be ruled out. IGR J18482+0049 represents a new obscured HMXB candidate with N_H =4 × 10²³ cm⁻². We tentatively propose that IGR J18532+0416 is either an AGN or a pulsar in an HMXB system. The X-ray spectral properties of IGR J18538−0102 are consistent with the AGN classification that has been proposed for this source.

Spectroscopic selection has been the most productive technique for the selection of galaxy-scale strong gravitational lens systems with known redshifts. Statistically significant samples of strong lenses provide a powerful method for measuring the mass-density parameters of the lensing population, but results can only be generalized to the parent population if the lensing selection biases are sufficiently understood. We perform controlled Monte Carlo simulations of spectroscopic lens surveys in order to quantify the bias of lenses relative to parent galaxies in velocity dispersion, mass axis ratio, and mass-density profile. For parameters typical of the SLACS and BELLS surveys, we find (1) no significant mass axis ratio detection bias of lenses relative to parent galaxies; (2) a very small detection bias toward shallow mass-density profiles, which is likely negligible compared to other sources of uncertainty in this parameter; (3) a detection bias toward smaller Einstein radius for systems drawn from parent populations with group- and cluster-scale lensing masses; and (4) a lens-modeling bias toward larger velocity dispersions for systems drawn from parent samples with sub-arcsecond mean Einstein radii. This last finding indicates that the incorporation of velocity-dispersion upper limits of non-lenses is an important ingredient for unbiased analyses of spectroscopically selected lens samples. In general, we find that the completeness of spectroscopic lens surveys in the plane of Einstein radius and mass-density profile power-law index is quite uniform, up to a sharp drop in the region of large Einstein radius and steep mass-density profile, and hence that such surveys are ideally suited to the study of massive field galaxies.

We present for the first time metallicity maps generated using data from the Wide Field Spectrograph on the ANU 2.3 m of 10 luminous infrared galaxies (LIRGs) and discuss the abundance gradients and distribution of metals in these systems. We have carried out optical integral field spectroscopy (IFS) of several LIRGs in various merger phases to investigate the merger process. In a major merger of two spiral galaxies with preexisting disk abundance gradients, the changing distribution of metals can be used as a tracer of gas flows in the merging system as low-metallicity gas is transported from the outskirts of each galaxy to their nuclei. We employ this fact to probe merger properties by using the emission lines in our IFS data to calculate the gas-phase metallicity in each system. We create abundance maps and subsequently derive a metallicity gradient from each map. We compare our measured gradients to merger stage as well as several possible tracers of merger progress and observed nuclear abundances. We discuss our work in the context of previous abundance gradient observations and compare our results to new galaxy merger models that trace metallicity gradient. Our results agree with the observed flattening of metallicity gradients as a merger progresses. We compare our results with new theoretical predictions that include chemical enrichment. Our data show remarkable agreement with these simulations.

We show that an α effect is driven by the cosmic-ray (CR) Bell instability exciting left–right asymmetric turbulence. Alfvén waves of a preferred polarization have maximally helical motion, because the transverse motion of each mode is parallel to its curl. We show how large-scale Alfvén modes, when rendered unstable by CR streaming, can create new net flux over any finite region, in the direction of the original large-scale field. We perform direct numerical simulations (DNSs) of a magnetohydrodynamic fluid with a forced CR current and use the test-field method to determine the α effect and the turbulent magnetic diffusivity. As follows from DNS, the dynamics of the instability has the following stages: (1) in the early stage, the small-scale Bell instability that results in the production of small-scale turbulence is excited; (2) in the intermediate stage, there is formation of larger-scale magnetic structures; (3) finally, quasi-stationary large-scale turbulence is formed at a growth rate that is comparable to that expected from the dynamo instability, but its amplitude over much longer timescales remains unclear. The results of DNS are in good agreement with the theoretical estimates. It is suggested that this dynamo is what gives weakly magnetized relativistic shocks such as those from gamma-ray bursts (GRBs) a macroscopic correlation length. It may also be important for large-scale magnetic field amplification associated with CR production and diffusive shock acceleration in supernova remnants (SNRs) and blast waves from GRBs. Magnetic field amplification by Bell turbulence in SNRs is found to be significant, but it is limited owing to the finite time available to the super-Alfvénicly expanding remnant. The effectiveness of the mechanisms is shown to be dependent on the shock velocity. Limits on magnetic field growth in longer-lived systems, such as the Galaxy and unconfined intergalactic CRs, are also discussed.

We present the first proper-motion (PM) measurements for the galaxy M31. We obtained new V-band imaging data with the Hubble Space Telescope ACS/WFC and the WFC3/UVIS instruments of three fields: a spheroid field near the minor axis, an outer disk field along the major axis, and a field on the Giant Southern Stream. The data provide five to seven year time baselines with respect to pre-existing deep first-epoch observations of the same fields. We measure the positions of thousands of M31 stars and hundreds of compact background galaxies in each field. High accuracy and robustness is achieved by building and fitting a unique template for each individual object. The average PM for each field is obtained from the average motion of the M31 stars between the epochs with respect to the background galaxies. For the three fields, the observed PMs (μ_W, μ_N) are, in units of mas yr⁻¹, (− 0.0458, −0.0376) ± (0.0165, 0.0154), (− 0.0533, −0.0104) ± (0.0246, 0.0244), and (− 0.0179, −0.0357) ± (0.0278, 0.0272), respectively. The ability to average over large numbers of objects and over the three fields yields a final displacement accuracy of a few thousandths of a pixel, corresponding to only 12 μas yr⁻¹. This is comparable to what has been achieved for other Local Group galaxies using Very Long Baseline Array observations of water masers. Potential systematic errors are controlled by an analysis strategy that corrects for detector charge transfer inefficiency, spatially and time-dependent geometric distortion, and point-spread function variations. The robustness of the PM measurements and uncertainties are supported by the fact that data from different instruments, taken at different times and with different telescope orientations, as well as measurements of different fields, all yield statistically consistent results. Papers II and III of this series explore the implications of the new measurements for our understanding of the history, future, and mass of the Local Group.

We determine the velocity vector of M31 with respect to the Milky Way and use this to constrain the mass of the Local Group, based on Hubble Space Telescope proper-motion measurements of three fields presented in Paper I. We construct N-body models for M31 to correct the measurements for the contributions from stellar motions internal to M31. This yields an unbiased estimate for the M31 center-of-mass motion. We also estimate the center-of-mass motion independently, using the kinematics of satellite galaxies of M31 and the Local Group, following previous work but with an expanded satellite sample. All estimates are mutually consistent, and imply a weighted average M31 heliocentric transverse velocity of (v_W, v_N) = (− 125.2 ± 30.8, −73.8 ± 28.4) km s⁻¹. We correct for the reflex motion of the Sun using the most recent insights into the solar motion within the Milky Way, which imply a larger azimuthal velocity than previously believed. This implies a radial velocity of M31 with respect to the Milky Way of V_{rad, M31} = −109.3 ± 4.4 km s⁻¹, and a tangential velocity of V_{tan, M31} = 17.0 km s⁻¹, with a 1σ confidence region of V_{tan, M31} ⩽ 34.3 km s⁻¹. Hence, the velocity vector of M31 is statistically consistent with a radial (head-on collision) orbit toward the Milky Way. We revise prior estimates for the Local Group timing mass, including corrections for cosmic bias and scatter, and obtain M_LG ≡ M_{MW, vir} + M_{M31, vir} = (4.93 ± 1.63) × 10¹² M_☉. Summing known estimates for the individual masses of M31 and the Milky Way obtained from other dynamical methods yields smaller uncertainties. Bayesian combination of the different estimates demonstrates that the timing argument has too much (cosmic) scatter to help much in reducing uncertainties on the Local Group mass, but its inclusion does tend to increase other estimates by ∼10%. We derive a final estimate for the Local Group mass from literature and new considerations of M_LG = (3.17 ± 0.57) × 10¹² M_☉. The velocity and mass results at 95% confidence imply that M33 is bound to M31, consistent with expectation from observed tidal deformations.

We study the future orbital evolution and merging of the Milky Way (MW)–M31–M33 system, using a combination of collisionless N-body simulations and semi-analytic orbit integrations. Monte Carlo simulations are used to explore the consequences of varying all relevant initial phase-space and mass parameters within their observational uncertainties. The observed M31 transverse velocity from Papers I and II implies that the MW and M31 will merge t = 5.86^+1.61_−0.72 Gyr from now. The first pericenter occurs at t = 3.87^+0.42_−0.32 Gyr, at a pericenter distance of r = 31.0^+38.0_−19.8 kpc. In 41% of Monte Carlo orbits, M31 makes a direct hit with the MW, defined here as a first-pericenter distance less than 25 kpc. For the M31–M33 system, the first-pericenter time and distance are t = 0.85^+0.18_−0.13 Gyr and r = 80.8^+42.2_−31.7 kpc. By the time M31 gets to its first pericenter with the MW, M33 is close to its second pericenter with M31. For the MW–M33 system, the first-pericenter time and distance are t = 3.70^+0.74_−0.46 Gyr and r = 176.0^+239.0_−136.9 kpc. The most likely outcome is for the MW and M31 to merge first, with M33 settling onto an orbit around them that may decay toward a merger later. However, there is a 9% probability that M33 makes a direct hit with the MW at its first pericenter, before M31 gets to or collides with the MW. Also, there is a 7% probability that M33 gets ejected from the Local Group, temporarily or permanently. The radial mass profile of the MW–M31 merger remnant is significantly more extended than the original profiles of either the MW or M31, and suggests that the merger remnant will resemble an elliptical galaxy. The Sun will most likely (∼85% probability) end up at a larger radius from the center of the MW–M31 merger remnant than its current distance from the MW center, possibly further than 50 kpc (∼10% probability). There is a ∼20% probability that the Sun will at some time in the next 10 Gyr find itself moving through M33 (within 10 kpc), but while dynamically still bound to the MW–M31 merger remnant. The arrival and possible collision of M31 (and possibly M33) with the MW is the next major cosmic event affecting the environment of our Sun and solar system that can be predicted with some certainty.

Using spatially resolved spectra obtained with the Low Resolution Imaging Spectrometer at the Keck I telescope, we investigate the nature of ionizing sources and kinematic properties of emission-line gas in a LINER galaxy SDSS J091628.05+420818.7, which is a nearby (z = 0.0241) and bright (M_r = −20.2) early-type galaxy. After subtracting stellar absorption features using a combination of simple stellar population models, we measure the flux, line-of-sight velocity, and velocity dispersion of four emission lines, i.e., Hα, Hβ, [O iii] λ5007, and [N ii] λ6584, to study radial change of emission-line fluxes and velocities. Compared to the point-spread function of the observation, the emission-line region is slightly extended but comparable to the seeing size. The central concentration of emission-line gas suggests that ionization is triggered by a nuclear source, excluding old stellar population as ionizing sources. We find that emission-line gas is counter-rotating with respect to stellar component and that the [O iii] λ5007 line is blueshifted compared to other emission lines, possibly due to an outflow.

We present an analytic model for the local bias of dark matter halos in a ΛCDM universe. The model uses the halo mass density instead of the halo number density and is searched for various halo mass cuts, smoothing lengths, and redshift epochs. We find that, when the logarithmic density is used, the second-order polynomial can fit the numerical relation between the halo mass distribution and the underlying matter distribution extremely well. In this model, the logarithm of the dark matter density is expanded in terms of log halo mass density to the second order. The model remains excellent for all halo mass cuts (from M_cut = 3 × 10¹¹ to 3 × 10¹² h⁻¹ M_☉), smoothing scales (from R = 5 h⁻¹ Mpc to 50 h⁻¹ Mpc), and redshift ranges (from z = 0 to 1.0) considered in this study. The stochastic term in the relation is found to be not entirely random, but a part of the term can be determined by the magnitude of the shear tensor.

We present spectroscopic observations and chemical abundances of 16 planetary nebulae (PNe) in the outer disk of M31. The [O iii] λ4363 line is detected in all objects, allowing a direct measurement of the nebular temperature essential for accurate abundance determinations. Our results show that the abundances in these M31 PNe display the same correlations and general behaviors as Type II PNe in the Milky Way. We also calculate photoionization models to derive estimates of central star properties. From these we infer that our sample PNe, all near the bright-end cutoff of the planetary nebula luminosity function, originated from stars near 2 M_☉. Finally, under the assumption that these PNe are located in M31's disk, we plot the oxygen abundance gradient, which appears shallower than the gradient in the Milky Way.

The possibility of the Lyβ fluorescence mechanism being operational in classical Be (CBe) stars and thereby contributing to the strength of the O i λ8446 line has been recognized for long. However, this supposition needs to be quantified by comparing observed and predicted O i line ratios. In the present work, optical and near-infrared spectra of CBe stars are presented. We analyze the observed strengths of the O i λ7774, λ8446, λ11287, and λ13165 lines, which have been theoretically proposed as diagnostics for identifying the excitation mechanism. We have considered and examined the effects of Lyβ fluorescence, collisional excitation, recombination, and continuum fluorescence on these O i line strengths. From our analysis it appears that the Lyβ fluorescence process is indeed operative in Be stars.

As the only directly imaged multiple planet system, HR 8799 provides a unique opportunity to study the physical properties of several planets in parallel. In this paper, we image all four of the HR 8799 planets at H band and 3.3 μm with the new Large Binocular Telescope adaptive optics system, PISCES, and LBTI/LMIRCam. Our images offer an unprecedented view of the system, allowing us to obtain H and 3.3 μm photometry of the innermost planet (for the first time) and put strong upper limits on the presence of a hypothetical fifth companion. We find that all four planets are unexpectedly bright at 3.3 μm compared to the equilibrium chemistry models used for field brown dwarfs, which predict that planets should be faint at 3.3 μm due to CH₄ opacity. We attempt to model the planets with thick-cloudy, non-equilibrium chemistry atmospheres but find that removing CH₄ to fit the 3.3 μm photometry increases the predicted L' (3.8 μm) flux enough that it is inconsistent with observations. In an effort to fit the spectral energy distribution of the HR 8799 planets, we construct mixtures of cloudy atmospheres, which are intended to represent planets covered by clouds of varying opacity. In this scenario, regions with low opacity look hot and bright, while regions with high opacity look faint, similar to the patchy cloud structures on Jupiter and L/T transition brown dwarfs. Our mixed-cloud models reproduce all of the available data, but self-consistent models are still necessary to demonstrate their viability.

We argue that current observations of M–σ relations for galaxies can be used to constrain theories of super-massive black holes (SMBHs) feeding. In particular, assuming that SMBH mass is limited only by the feedback on the gas that feeds it, we show that SMBHs fed via a planar galaxy-scale gas flow, such as a disk or a bar, should be much more massive than their counterparts fed by quasi-spherical inflows. This follows from the relative inefficiency of active galactic nucleus feedback on a flattened inflow. We find that even under the most optimistic conditions for SMBH feedback on flattened inflows, the mass at which the SMBH expels the gas disk and terminates its own growth is a factor of several higher than the one established for quasi-spherical inflows. Any beaming of feedback away from the disk and any disk self-shadowing strengthen this result further. Contrary to this theoretical expectation, recent observations have shown that SMBHs in pseudobulge galaxies (which are associated with barred galaxies) are typically under- rather than overmassive when compared with their classical bulge counterparts at a fixed value of σ. We conclude from this that SMBHs are not fed by large (100 pc to many kpc) scale gas disks or bars, most likely because such planar flows are turned into stars too efficiently to allow any SMBH growth. Based on this and other related observational evidence, we argue that most SMBHs grow by chaotic accretion of gas clouds with a small and nearly randomly distributed direction of angular momentum.

The star formation rates (SFRs) of low-metallicity galaxies depend sensitively on the gas metallicity, because metals are crucial to mediating the transition from intermediate-temperature atomic gas to cold molecular gas, a necessary precursor to star formation. We study the impact of this effect on the star formation history of galaxies. We incorporate metallicity-dependent star formation and metal enrichment in a simple model that follows the evolution of a halo main progenitor. Our model shows that including the effect of metallicity leads to suppression of star formation at redshift z > 2 in dark halos with masses ≲ 10¹¹ M_☉, with the suppression becoming near total for halos below ∼10^9.5–10¹⁰ M_☉. We find that at high redshift, until z ∼ 2, the SFR cannot catch up with the gas inflow rate (IR), because the SFR is limited by the free-fall time, and because it is suppressed further by a lack of metals in small halos. As a result, in each galaxy the SFR is growing in time faster than the IR, and the integrated cosmic SFR density is rising with time. The suppressed in situ SFR at high-z makes the growth of stellar mass dominated by ex situ SFR, meaning stars formed in lower mass progenitor galaxies and then accreted, which implies that the specific SFR (sSFR) remains constant with time. The intensely accreted gas at high-z is accumulating as an atomic gas reservoir. This provides additional fuel for star formation in 10¹⁰–10¹² M_☉ halos at z ∼ 1–3, which allows the SFR to exceed the instantaneous IR, and may enable an even higher outflow rate. At z < 1, following the natural decline in IR with time due to the universal expansion, the SFR and sSFR are expected to drop. We specify the expected dependence of sSFR and metallicity on stellar mass and redshift. At a given z, and below a critical mass, these relations are predicted to be flat and rising, respectively. Our model predictions qualitatively match some of the puzzling features in the observed star formation history.

With high-resolution (0.46 h⁻¹ kpc), large-scale, adaptive mesh-refinement Eulerian cosmological hydrodynamic simulations we compute properties of O vi and O vii absorbers from the warm-hot intergalactic medium (WHIM) at z = 0. Our new simulations are in broad agreement with previous simulations with ∼40% of the intergalactic medium being in the WHIM. Our simulations are in agreement with observed properties of O vi absorbers with respect to the line incidence rate and Doppler-width–column-density relation. It is found that the amount of gas in the WHIM below and above 10⁶ K is roughly equal. Strong O vi absorbers are found to be predominantly collisionally ionized. It is found that (61%, 57%, 39%) of O vi absorbers of log N(O vi) cm² = (12.5–13, 13–14, > 14) have T < 10⁵ K. Cross correlations between galaxies and strong [N(O vi) > 10¹⁴ cm⁻²] O vi absorbers on ∼100–300 kpc scales are suggested as a potential differentiator between collisional ionization and photoionization models. Quantitative prediction is made for the presence of broad and shallow O vi lines that are largely missed by current observations but will be detectable by Cosmic Origins Spectrograph observations. The reported 3σ upper limit on the mean column density of coincidental O vii lines at the location of detected O vi lines by Yao et al. is above our predicted value by a factor of 2.5–4. The claimed observational detection of O vii lines by Nicastro et al., if true, is 2σ above what our simulations predict.

High-resolution FTIR spectra of ethylene oxide have been measured in the far-infrared region using synchrotron radiation. A total of 1182 lines between 15 and 73 cm⁻¹ were assigned, with J_max = 64, expanding upon previous studies that had recorded spectra up to 12 cm⁻¹, J_max = 49. All available data were co-fitted to provide greatly imp- roved rotational constants for the ground vibrational state that are capable of predicting transitions up to 73 cm⁻¹.

We present the 1.9–4.2 μm spectra of the five bright (L ⩽ 11.2) young stars associated with silhouette disks with a moderate to high inclination angle of 39°–80° in the M42 and M43 regions. The water ice absorption is seen toward d121-1925 and d216-0939, while the spectra of d182-316, d183-405, and d218-354 show no water ice feature around 3.1 μm within the detection limits. By comparing the water ice features toward nearby stars, we find that the water ice absorption toward d121-1925 and d216-0939 most likely originates from the foreground material and the surrounding disk, respectively. The angle of the disk inclination is found to be mainly responsible for the difference of the optical depth of the water ice among the five young stars. Our results suggest that there is a critical inclination angle between 65° and 75° for the circumstellar disk where the water ice absorption becomes strong. The average density at the disk surface of d216-0939 was found to be 6.38 × 10⁻¹⁸ g cm⁻³. The water ice absorption band in the d216-0939 disk is remarkable in that the maximum optical depth of the water ice band is at a longer wavelength than detected before. It indicates that the primary carrier of the feature is purely crystallized water ice at the surface of the d216-0939 disk with characteristic size of ∼0.8 μm, which suggests grain growth. This is the first direct detection of purely crystallized water ice in a silhouette disk.

Spectral energy distributions are computed using two-dimensional (2D) rotating stellar models and non-LTE plane-parallel model atmospheres. A rotating, 2D stellar model has been found that matches the observed ultraviolet and visible spectrum of α Oph. The SED match occurs for the interferometrically deduced surface shape and inclination, and is different from the SED produced by spherical models. The p-mode oscillation frequencies in which the latitudinal variation is modeled by a linear combination of eight Legendre polynomials were computed for this model. The five highest and seven of the nine highest amplitude modes show agreement between computed axisymmetric, equatorially symmetric mode frequencies and the mode frequencies observed by the Microvariability and Oscillations of Stars satellite (MOST) to within the observational error. Including nonaxisymmetric modes up through |m| = 2, and allowing for the possibility that the eight lowest amplitude modes could be produced by modes that are not equatorially symmetric, matches for 24 out of the 35 MOST modes to within the observational error and another eight modes to within twice the observational error. The remaining three observed modes can be fitted within 4.2 times the observational error, but even these may be fitted to within the observational error if the criteria for computed modes are expanded.

It has been suggested that type II radio bursts are due to energetic electrons accelerated at coronal shocks. Radio observations, however, have poor or no spatial resolutions to pinpoint the exact acceleration locations of these electrons. In this paper, we discuss a promising approach to infer the electron acceleration location by combining radio and white light observations. The key assumption is to relate specific morphological features (e.g., spectral bumps) of the dynamic spectra of type II radio bursts to imaging features (e.g., coronal mass ejection (CME) going into a streamer) along the CME (and its driven shock) propagation. In this study, we examine the CME–streamer interaction for the solar eruption dated on 2003 November 1. The presence of spectral bump in the relevant type II radio burst is identified, which is interpreted as a natural result of the shock-radio-emitting region entering the dense streamer structure. The study is useful for further determinations of the location of type II radio burst and the associated electron acceleration by CME-driven shock.

We present the earliest ultraviolet (UV) observations of the bright Type Ia supernova SN 2011fe/PTF11kly in the nearby galaxy M101 at a distance of only 6.4 Mpc. It was discovered shortly after explosion by the Palomar Transient Factory and first observed by Swift/UVOT about a day after explosion. The early UV light is well defined, with ∼20 data points per filter in the five days after explosion. These early and well-sampled UV observations form new template light curves for comparison with observations of other SNe Ia at low and high redshift. We report fits from semiempirical models of the explosion and find the time evolution of the early UV flux to be well fitted by the superposition of two parabolic curves. Finally, we use the early UV flux measurements to examine a possible shock interaction with a non-degenerate companion. From models predicting the measurable shock emission, we find that even a solar mass companion at a distance of a few solar radii is unlikely at more than 95% confidence.

The wide-area imaging surveys with the HerschelSpace Observatory at submillimeter (sub-mm) wavelengths have now resulted in catalogs of the order of one-hundred-thousand dusty, starburst galaxies. These galaxies capture an important phase of galaxy formation and evolution, but, unfortunately, the redshift distribution of these galaxies, N(z), is still mostly uncertain due to limitations associated with counterpart identification at optical wavelengths and spectroscopic follow-up. We make a statistical estimate of N(z) using a clustering analysis of sub-mm galaxies detected at each of 250, 350 and 500 μm from the Herschel Multi-tiered Extragalactic Survey centered on the Boötes field. We cross-correlate Herschel galaxies against galaxy samples at optical and near-IR wavelengths from the Sloan Digital Sky Survey, the NOAO Deep Wide Field Survey, and the Spitzer Deep Wide Field Survey. We create optical and near-IR galaxy samples based on their photometric or spectroscopic redshift distributions and test the accuracy of those redshift distributions with similar galaxy samples defined with catalogs from the Cosmological Evolution Survey (COSMOS), which has superior spectroscopic coverage. We model the clustering auto- and cross-correlations of Herschel and optical/IR galaxy samples to estimate N(z) and clustering bias factors. The S₃₅₀  >  20 mJy galaxies have a bias factor varying with redshift as b(z) = 1.0^+1.0_{− 0.5}(1 + z)^{1.2+0.3_{− 0.7}}. This bias and the redshift dependence is broadly in agreement with galaxies that occupy dark matter halos of mass in the range of 10¹² to 10¹³M_☉. We find that galaxy selections in all three Spectral and Photometric Imaging Receiver (SPIRE) bands share a similar average redshift, with 〈z〉 = 1.8 ± 0.2 for 250 μm selected samples, and 〈z〉 = 1.9 ± 0.2 for both 350 and 500 μm samples, while their distributions behave differently. For 250 μm selected galaxies we find the a larger number of sources with z ⩽ 1 when compared with the subsequent two SPIRE bands, with 350 and 500 μm selected SPIRE samples having peaks in N(z) at progressively higher redshifts. We compare our clustering-based N(z) results to sub-mm galaxy model predictions in the literature, and with an estimate of N(z) using a stacking analysis of COSMOS 24 μm detections.

Giant X-ray cavities lie in some active galactic nuclei (AGNs) locating in central galaxies of clusters, which are estimated to have stored 10⁵⁵–10⁶² erg of energy. Most of these cavities are thought to be inflated by jets of AGNs on a timescale of ≳ 10⁷ years. The jets can be either powered by rotating black holes or the accretion disks surrounding black holes, or both. The observations of giant X-ray cavities can therefore be used to constrain jet formation mechanisms. In this work, we choose the most energetic cavity, MS 0735+7421, with stored energy ∼10⁶² erg, to constrain the jet formation mechanisms and the evolution of the central massive black hole in this source. The bolometric luminosity of the AGN in this cavity is ∼10⁻⁵L_Edd, however, the mean power of the jet required to inflate the cavity is estimated as ∼0.02L_Edd, which implies that the source has previously experienced strong outbursts. During outbursts, the jet power and the mass accretion rate should be significantly higher than its present values. We construct an accretion disk model in which the angular momentum and energy carried away by jets are properly included to calculate the spin and mass evolution of the massive black hole. In our calculations, different jet formation mechanisms are employed, and we find that the jets generated with the Blandford–Znajek (BZ) mechanism are unable to produce the giant cavity with ∼10⁶² erg in this source. Only the jets accelerated with a combination of the Blandford–Payne and BZ mechanisms can successfully inflate such a giant cavity if the magnetic pressure is close to equipartition with the total (radiation+gas) pressure of the accretion disk. For a dynamo-generated magnetic field in the disk, such an energetic giant cavity can be inflated by the magnetically driven jets only if the initial black hole spin parameter a₀ ≳ 0.95. Our calculations show that the final spin parameter a of the black hole is always ∼0.9–0.998 for all the computational examples that can provide sufficient energy for the cavity of MS 0735+7421.

The presence of a well-defined and narrow dust lane in an edge-on spiral galaxy is the observational signature of a thin and dense molecular disk, in which gravitational collapse has overcome turbulence. Using a sample of galaxies out to z ∼ 1 extracted from the COSMOS survey, we identify the fraction of massive (L*_V) disks that display a dust lane. Our goal is to explore the evolution in the stability of the molecular interstellar medium (ISM) disks in spiral galaxies over a cosmic timescale. We check the reliability of our morphological classifications against changes in rest-frame wavelength, resolution, and cosmic dimming with (artificially redshifted) images of local galaxies from the Sloan Digital Sky Survey. We find that the fraction of L*_V disks with dust lanes in COSMOS is consistent with the local fraction (≈80%) out to z ∼ 0.7. At z = 0.8, the dust lane fraction is only slightly lower. A somewhat lower dust lane fraction in starbursting galaxies tentatively supports the notion that a high specific star formation rate can efficiently destroy or inhibit a dense molecular disk. A small subsample of higher redshift COSMOS galaxies display low internal reddening (E[B − V]), as well as a low incidence of dust lanes. These may be disks in which the growth of the dusty ISM disk lags behind that of the stellar disk. We note that at z = 0.8, the most massive galaxies display a lower dust lane fraction than lower mass galaxies. A small contribution of recent mergers or starbursts to this most massive population may be responsible. The fact that the fraction of galaxies with dust lanes in COSMOS is consistent with little or no evolution implies that models to explain the spectral energy distribution or the host galaxy dust extinction of supernovae based on local galaxies are still applicable to higher redshift spirals. It also suggests that dust lanes are long-lived phenomena or can be reformed over very short timescales.

We present a multi-wavelength photometric study of ∼15,000 resolved stars in the nearby spiral galaxy M83 (NGC 5236, D = 4.61 Mpc) based on HubbleSpaceTelescope Wide Field Camera 3 observations using four filters: F336W, F438W, F555W, and F814W. We select 50 regions (an average size of 260 pc by 280 pc) in the spiral arm and inter-arm areas of M83 and determine the age distribution of the luminous stellar populations in each region. This is accomplished by correcting for extinction toward each individual star by comparing its colors with predictions from stellar isochrones. We compare the resulting luminosity-weighted mean ages of the luminous stars in the 50 regions with those determined from several independent methods, including the number ratio of red-to-blue supergiants, morphological appearance of the regions, surface brightness fluctuations, and the ages of clusters in the regions. We find reasonably good agreement between these methods. We also find that young stars are much more likely to be found in concentrated aggregates along spiral arms, while older stars are more dispersed. These results are consistent with the scenario that star formation is associated with the spiral arms, and stars form primarily in star clusters and then disperse on short timescales to form the field population. The locations of Wolf–Rayet stars are found to correlate with the positions of many of the youngest regions, providing additional support for our ability to accurately estimate ages. We address the effects of spatial resolution on the measured colors, magnitudes, and age estimates. While individual stars can occasionally show measurable differences in the colors and magnitudes, the age estimates for entire regions are only slightly affected.

We have developed a new needlet-based method to detect point sources in cosmic microwave background (CMB) maps and have applied it to the Wilkinson Microwave Anisotropy Probe (WMAP) 7 year data. We use both the individual frequency channels as well as internal templates, the latter being the difference between pairs of frequency channels and hence having the advantage that the CMB component is eliminated. Using the area of the sky outside the Kq85 galactic mask, we detect a total of 2102 point sources at the 5σ level in either the frequency maps or the internal templates. Of these, 1116 are detected either at 5σ directly in the frequency channels or at 5σ in the internal templates and ⩾3σ at the corresponding position in the frequency channels. Of the 1116 sources, 603 are detections that have not been reported so far in WMAP data. We have made a catalog of these sources available with position and flux estimated in the WMAP channels where they are seen. In total, we identified 1029 of the 1116 sources with counterparts at 5 GHz and 69 at other frequencies.

We investigate the acceleration of charged particles (both electrons and protons) at collisionless shocks predicted to exist in the vicinity of solar flares. The existence of standing termination shocks has been examined by flare models and numerical simulations. We study electron energization by numerically integrating the equations of motion of a large number of test-particle electrons in the time-dependent two-dimensional electric and magnetic fields generated from hybrid simulations (kinetic ions and fluid electron) using parameters typical of the solar flare plasma environment. The shock is produced by injecting plasma flow toward a rigid piston. Large-scale magnetic fluctuations—known to exist in plasmas and known to have important effects on the nonthermal electron acceleration at shocks—are also included in our simulations. For the parameters characteristic of the flaring region, our calculations suggest that the termination shock formed in the reconnection outflow region (above post-flare loops) could accelerate electrons to a kinetic energy of a few MeV within 100 ion cyclotron periods, which is of the order of a millisecond. Given a sufficient turbulence amplitude level (δB²/B²₀ ∼ 0.3), about 10% of thermal test-particle electrons are accelerated to more than 15 keV. We find that protons are also accelerated, but not to as high energy in the available time and the energy spectra are considerably steeper than that of the electrons for the parameters used in our simulations. Our results are qualitatively consistent with the observed hard X-ray emissions in solar flares.

We combine dynamical and non-equilibrium chemical modeling of evolving prestellar molecular cloud cores and investigate the evolution of molecular abundances in the contracting core. We model both magnetic cores, with varying degrees of initial magnetic support, and non-magnetic cores, with varying collapse delay times. We explore, through a parameter study, the competing effects of various model parameters in the evolving molecular abundances, including the elemental C/O ratio, the temperature, and the cosmic-ray ionization rate. We find that different models show their largest quantitative differences at the center of the core, whereas the outer layers, which evolve slower, have abundances which are severely degenerate among different dynamical models. There is a large range of possible abundance values for different models at a fixed evolutionary stage (central density), which demonstrates the large potential of chemical differentiation in prestellar cores. However, degeneracies among different models, compounded with uncertainties induced by other model parameters, make it difficult to discriminate among dynamical models. To address these difficulties, we identify abundance ratios between particular molecules, the measurement of which would have maximal potential for discrimination among the different models examined here. In particular, we find that the ratios between NH₃ and CO, NH₂ and CO, and NH₃ and HCO⁺ are sensitive to the evolutionary timescale, and that the ratio between HCN and OH is sensitive to the C/O ratio. Finally, we demonstrate that measurements of the central deviation (central depletion or enhancement) of abundances of certain molecules are good indicators of the dynamics of the core.

The Wide-field Infrared Survey Explorer (WISE) is an extremely capable and efficient black hole finder. We present a simple mid-infrared color criterion, W1 − W2 ⩾ 0.8 (i.e., [3.4]−[4.6] ⩾0.8, Vega), which identifies 61.9 ± 5.4 active galactic nucleus (AGN) candidates per deg² to a depth of W2 ∼ 15.0. This implies a much larger census of luminous AGNs than found by typical wide-area surveys, attributable to the fact that mid-infrared selection identifies both unobscured (type 1) and obscured (type 2) AGNs. Optical and soft X-ray surveys alone are highly biased toward only unobscured AGNs, while this simple WISE selection likely identifies even heavily obscured, Compton-thick AGNs. Using deep, public data in the COSMOS field, we explore the properties of WISE-selected AGN candidates. At the mid-infrared depth considered, 160 μJy at 4.6 μm, this simple criterion identifies 78% of Spitzer mid-infrared AGN candidates according to the criteria of Stern et al. and the reliability is 95%. We explore the demographics, multiwavelength properties and redshift distribution of WISE-selected AGN candidates in the COSMOS field.

The electron velocity distribution function is studied in the extended solar corona above coronal holes (i.e., the inner part of the fast solar wind) from the highly collisional corona close to the Sun to the weakly collisional regions farther out. The electron kinetic equation is solved with a finite-element method in velocity space using a linearized Fokker–Planck collision operator. The ion density and temperature profiles are assumed to be known and the electric field and electron temperature are determined self-consistently. The results show quantitatively how much lower the electron heat flux and the thermal force are than predicted by high-collisionality theory. The sensitivity of the particle and heat fluxes to the assumed ion temperature profile and the applied boundary condition at the boundary far from the Sun is also studied.

Numerous studies have investigated the role of thermal instability in regulating the phase transition between the cold cloudy and warm diffuse medium of the interstellar medium. Considerable interest has also been devoted to investigating the properties of turbulence in thermally unstable flows, with a special emphasis on molecular clouds and the possibility of star formation. In this study, we investigate another setting in which this instability may be important, namely its effect on dynamo action in interstellar flows. The setup we consider is a three-dimensional periodic cube of gas with an initially weak magnetic field, subject to heating and cooling, the properties of which are such that thermal instability is provoked in a certain temperature regime. Dynamo action is established through external forcing on the flow field. By comparing the results with a cooling function with exactly the same net effect but no thermally unstable regime, we find the following. Reference runs with non-helical forcing were observed to produce no small-scale dynamo action below the Reynolds number 97. Therefore, we expect the magnetic fields generated in the helical runs to be purely due to the action of a large-scale dynamo mechanism. The critical Reynolds number for the onset of the large-scale dynamo was observed to roughly double between the thermally stable versus unstable runs, the conclusion being that the thermal instability makes large-scale dynamo action more difficult. Whereas density and magnetic fields were observed to be almost completely uncorrelated in the thermally stable cases investigated, the action of thermal instability was observed to produce a positive correlation of the form B∝ρ^0.2. This correlation is rather weak, and in addition it was observed to break down at the limit of highest densities.

We report Herschel SPIRE (250, 350, and 500 μm) detections of 32 quasars with redshifts 0.5 ⩽z < 3.6 from the Herschel Multi-tiered Extragalactic Survey (HerMES). These sources are from a MIPS 24 μm flux-limited sample of 326 quasars in the Lockman Hole Field. The extensive multi-wavelength data available in the field permit construction of the rest-frame spectral energy distributions (SEDs) from ultraviolet to the mid-infrared for all sources, and to the far-infrared (FIR) for the 32 objects. Most quasars with Herschel FIR detections show dust temperatures in the range of 25–60 K, with a mean of 34 K. The FIR luminosities range from 10^11.3 to 10^13.5  L_☉, qualifying most of their hosts as ultra- or hyper-luminous infrared galaxies. These FIR-detected quasars may represent a dust-rich population, but with lower redshifts and fainter luminosities than quasars observed at ∼1 mm. However, their FIR properties cannot be predicted from shorter wavelengths (0.3–20 μm, rest frame), and the bolometric luminosities derived using the 5100 Å index may be underestimated for these FIR-detected quasars. Regardless of redshift, we observed a decline in the relative strength of FIR luminosities for quasars with higher near-infrared luminosities.

We present high angular resolution observations (05 × 03) carried out with the Submillimeter Array (SMA) toward the AFGL2591 high-mass star-forming region. Our SMA images reveal a clear chemical segregation within the AFGL2591 VLA 3 hot core, where different molecular species (Types I, II, and III) appear distributed in three concentric shells. This is the first time that such a chemical segregation is ever reported at linear scales ⩽3000 AU within a hot core. While Type I species (H₂S and ¹³CS) peak at the AFGL2591 VLA 3 protostar, Type II molecules (HC₃N, OCS, SO, and SO₂) show a double-peaked structure circumventing the continuum peak. Type III species, represented by CH₃OH, form a ring-like structure surrounding the continuum emission. The excitation temperatures of SO₂, HC₃N, and CH₃OH (185 ± 11 K, 150 ± 20 K, and 124 ± 12 K, respectively) show a temperature gradient within the AFGL2591 VLA 3 envelope, consistent with previous observations and modeling of the source. By combining the H₂S, SO₂, and CH₃OH images, representative of the three concentric shells, we find that the global kinematics of the molecular gas follow Keplerian-like rotation around a 40 M_☉ star. The chemical segregation observed toward AFGL2591 VLA 3 is explained by the combination of molecular UV photodissociation and a high-temperature (∼1000 K) gas-phase chemistry within the low extinction innermost region in the AFGL2591 VLA 3 hot core.

A well-known behavior of EUV light curves of discrete coronal loops is that the peak intensities of cooler channels or spectral lines are reached at progressively later times than hotter channels. This time lag is understood to be the result of hot coronal loop plasma cooling through these lower respective temperatures. However, loops typically comprise only a minority of the total emission in active regions (ARs). Is this cooling pattern a common property of AR coronal plasma, or does it only occur in unique circumstances, locations, and times? The new Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) data provide a wonderful opportunity to answer this question systematically for an entire AR. We measure the time lag between pairs of SDO/AIA EUV channels using 24 hr of images of AR 11082 observed on 2010 June 19. We find that there is a time-lag signal consistent with cooling plasma, just as is usually found for loops, throughout the AR including the diffuse emission between loops for the entire 24 hr duration. The pattern persists consistently for all channel pairs and choice of window length within the 24 hr time period, giving us confidence that the plasma is cooling from temperatures of greater than 3 MK, and sometimes exceeding 7 MK, down to temperatures lower than ∼0.8 MK. This suggests that the bulk of the emitting coronal plasma in this AR is not steady; rather, it is dynamic and constantly evolving. These measurements provide crucial constraints on any model which seeks to describe coronal heating.

We have measured the widths of spectral lines from a polar coronal hole using the Extreme Ultraviolet Imaging Spectrometer on board Hinode. Polar coronal holes are regions of open magnetic field and the source of the fast solar wind. We find that the line widths decrease at relatively low heights. Previous observations have attributed such decreases to systematic effects, but we find that such effects are too small to explain our results. We conclude that the line narrowing is real. The non-thermal line widths are believed to be proportional to the amplitude of Alfvén waves propagating along these open field lines. Our results suggest that Alfvén waves are damped at unexpectedly low heights in a polar coronal hole. We derive an estimate on the upper limit for the energy dissipated between 1.1 R_☉ and 1.3 R_☉ and find that it is enough to account for up to 70% of that required to heat the polar coronal hole and accelerate the solar wind.

Studying the Doppler shifts and the temperature dependence of Doppler shifts in moss regions can help us understand the heating processes in the core of the active regions. In this paper, we have used an active region observation recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) on board Hinode on 2007 December 12 to measure the Doppler shifts in the moss regions. We have distinguished the moss regions from the rest of the active region by defining a low-density cutoff as derived by Tripathi et al. in 2010. We have carried out a very careful analysis of the EIS wavelength calibration based on the method described by Young et al. in 2012. For spectral lines having maximum sensitivity between log  T = 5.85 and log  T = 6.25 K, we find that the velocity distribution peaks at around 0 km s⁻¹ with an estimated error of 4–5 km s⁻¹. The width of the distribution decreases with temperature. The mean of the distribution shows a blueshift which increases with increasing temperature and the distribution also shows asymmetries toward blueshift. Comparing these results with observables predicted from different coronal heating models, we find that these results are consistent with both steady and impulsive heating scenarios. However, the fact that there are a significant number of pixels showing velocity amplitudes that exceed the uncertainty of 5 km s⁻¹ is suggestive of impulsive heating. Clearly, further observational constraints are needed to distinguish between these two heating scenarios.

Using high-resolution Chandra data, we report the presence of a weak X-ray point source coincident with the nucleus of NGC 4178, a late-type bulgeless disk galaxy known to have high-ionization mid-infrared (mid-IR) lines typically associated with active galactic nuclei (AGNs). Although the faintness of this source precludes a direct spectral analysis, we are able to infer its basic spectral properties using hardness ratios. X-ray modeling, combined with the nuclear mid-IR characteristics, suggests that NGC 4178 may host a highly absorbed AGN accreting at a high rate with a bolometric luminosity on order of 10⁴³ erg s⁻¹. The black hole mass estimate, based on our Chandra data and archival Very Large Array data using the most recent fundamental plane relations, is ∼10⁴–10⁵ M_☉, possibly the lowest mass nuclear black hole currently known. There are also three off-nuclear sources, two with a similar brightness to the nuclear source at 36'' and 32'' from the center. As with the nuclear source, hardness ratios are used to estimate spectra for these two sources, and both are consistent with a simple power-law (PL) model with absorption. These two sources have X-ray luminosities of the order of ∼10³⁸ erg s⁻¹, which place them at the threshold between X-ray binaries and ultraluminous X-ray sources (ULXs). The third off-nuclear source, located 49'' from the center, is the brightest source detected, with an X-ray luminosity of ∼10⁴⁰ erg s⁻¹. Its spectrum is well fit with an absorbed PL model, suggesting that it is a ULX. We also fit its spectrum with the Bulk Motion Comptonization model and suggest that this source is consistent with an intermediate-mass black hole of mass (6 ± 2) × 10³ M_☉.

We present long-slit spectrophotometry of two H ii galaxies: TOL 2146−391 and TOL 0357−3915. We performed a detailed analysis that involves abundance determinations relaxing the assumption of homogeneous temperature. The temperature inhomogeneity values, t², were obtained through two methods: (1) comparing abundances from oxygen recombination lines to abundances from collisionally excited lines and (2) by using the line intensity ratios of a set of He i lines together with the helio10 program. We find that the helio10 program is a good alternative to obtain a t² value in photoionized regions where recombination lines of heavy elements are not available. We have plotted 27 high- and low-metallicity H ii regions in an oxygen degree of ionization versus t² diagram; we find areas populated by H ii regions and areas void of them; the physical characteristics of each area are discussed. In addition, an average t² value can be determined for the objects in each area. We propose to use this 〈t²〉 value for the cases where a direct measurement of t² cannot be determined.

The Pierre Auger Observatory has associated a few ultra-high energy cosmic rays (UHECRs) with the direction of Centaurus A. This source has been deeply studied in radio, infrared, X-ray, and γ-rays (MeV–TeV) because it is the nearest radio-loud active galactic nucleus. Its spectral energy distribution or spectrum shows two main peaks, the low-energy peak, at an energy of 10⁻² eV, and the high-energy peak, at about 150 keV. There is also a faint very high energy (VHE; E ⩾ 100 GeV) γ-ray emission fully detected by the High Energy Stereoscopic System experiment. In this work, we describe the entire spectrum: the two main peaks with a synchrotron/synchrotron self-Compton model, and the VHE emission with a hadronic model. We consider pγ and pp interactions. For the pγ interaction, we assume that the target photons are those produced at 150 keV in leptonic processes. On the other hand, for the pp interaction we consider as targets the thermal particle densities in the lobes. Requiring a satisfactory description of the spectra at very high energies with pγ interaction, we obtain an excessive luminosity in UHECRs (even exceeding the Eddington luminosity). However, when considering the pp interaction to describe the γ-spectrum, the number of UHECRs obtained is in agreement with Pierre Auger observations. We also calculate the possible neutrino signal from pp interactions on a Km³ neutrino telescope using Monte Carlo simulations.

Recently, detections of a high-energy γ-ray source at the position of the Galactic center have been reported by multiple γ-ray telescopes, spanning the energy range between 100 MeV and 100 TeV. Analysis of these signals strongly suggests the TeV emission to have a morphology consistent with a point source up to the angular resolution of the HESS telescope (approximately 3 pc), while the point-source nature of the GeV emission is currently unsettled, with indications that it may be spatially extended. In the case that the emission is hadronic and in a steady state, we show that the expected γ-ray morphology is dominated by the distribution of target gas, rather than by details of cosmic-ray injection and propagation. Specifically, we expect a significant portion of hadronic emission to coincide with the position of the circumnuclear ring, which resides between 1 and 3 pc from the Galactic center. We note that the upcoming Cherenkov Telescope Array (CTA) will be able to observe conclusive correlations between the morphology of the TeV γ-ray source and the observed gas density, convincingly confirming or ruling out a hadronic origin for the γ-ray emission.

Merger-remnant galaxies with kiloparsec (kpc) scale separation dual active galactic nuclei (AGNs) should be widespread as a consequence of galaxy mergers and triggered gas accretion onto supermassive black holes, yet very few dual AGNs have been observed. Galaxies with double-peaked narrow AGN emission lines in the Sloan Digital Sky Survey (SDSS) are plausible dual AGN candidates, but their double-peaked profiles could also be the result of gas kinematics or AGN-driven outflows and jets on small or large scales. To help distinguish between these scenarios, we have obtained spatial profiles of the AGN emission via follow-up long-slit spectroscopy of 81 double-peaked narrow-line AGNs in SDSS at 0.03 ⩽ z ⩽ 0.36 using Lick, Palomar, and MMT Observatories. We find that all 81 systems exhibit double AGN emission components with ∼kpc projected spatial separations on the sky (0.2 h⁻¹₇₀ kpc <Δx < 5.5 h⁻¹₇₀ kpc; median Δx = 1.1 h⁻¹₇₀ kpc), which suggests that they are produced by kiloparsec-scale dual AGNs or kiloparsec-scale outflows, jets, or rotating gaseous disks. Further, the objects split into two subpopulations based on the spatial extent of the double emission components and the correlation between projected spatial separations and line-of-sight velocity separations. These results suggest that the subsample (58⁺⁵_{− 6}%) of the objects with spatially compact emission components may be preferentially produced by dual AGNs, while the subsample (42⁺⁶_{− 5}%) with spatially extended emission components may be preferentially produced by AGN outflows. We also find that for 32⁺⁸_{− 6}% of the sample the two AGN emission components are preferentially aligned with the host galaxy major axis, as expected for dual AGNs orbiting in the host galaxy potential. Our results both narrow the list of possible physical mechanisms producing the double AGN components, and suggest several observational criteria for selecting the most promising dual AGN candidates from the full sample of double-peaked narrow-line AGNs. Using these criteria, we determine the 17 most compelling dual AGN candidates in our sample.

Tidal debris around galaxies can yield important clues on their evolution. We have identified tidal debris in 11 early-type galaxies (T ⩽ 0) from a sample of 65 early types drawn from the Spitzer Survey of Stellar Structure in Galaxies (S⁴G). The tidal debris includes features such as shells, ripples, and tidal tails. A variety of techniques, including two-dimensional decomposition of galactic structures, were used to quantify the residual tidal features. The tidal debris contributes ∼3%–10% to the total 3.6 μm luminosity of the host galaxy. Structural parameters of the galaxies were estimated using two-dimensional profile fitting. We investigate the locations of galaxies with tidal debris in the fundamental plane and Kormendy relation. We find that galaxies with tidal debris lie within the scatter of early-type galaxies without tidal features. Assuming that the tidal debris is indicative of recent gravitational interaction or merger, this suggests that these galaxies have either undergone minor merging events so that the overall structural properties of the galaxies are not significantly altered, or they have undergone a major merging events but already have experienced sufficient relaxation and phase mixing so that their structural properties become similar to those of the non-interacting early-type galaxies.

We explore the effects of mergers on the evolution of massive early-type galaxies by modeling the evolution of their stellar populations in a hierarchical context. We investigate how a realistic red sequence population set up by z  ∼  1 evolves under different assumptions for the merger and star formation histories, comparing changes in color, luminosity, and mass. The purely passive fading of existing red sequence galaxies, with no further mergers or star formation, results in dramatic changes at the bright end of the luminosity function and color–magnitude relation. Without mergers there is too much evolution in luminosity at a fixed space density compared to observations. The change in color and magnitude at a fixed mass resembles that of a passively evolving population that formed relatively recently, at z  ∼  2. Mergers among the red sequence population ("dry mergers") occurring after z = 1 build up mass, counteracting the fading of the existing stellar populations to give smaller changes in both color and luminosity for massive galaxies. By allowing some galaxies to migrate from the blue cloud onto the red sequence after z = 1 through gas-rich mergers, younger stellar populations are added to the red sequence. This manifestation of the progenitor bias increases the scatter in age and results in even smaller changes in color and luminosity between z = 1 and z = 0 at a fixed mass. The resultant evolution appears much slower, resembling the passive evolution of a population that formed at high redshift (z  ∼  3–5), and is in closer agreement with observations. We conclude that measurements of the luminosity and color evolution alone are not sufficient to distinguish between the purely passive evolution of an old population and cosmologically motivated hierarchical growth, although these scenarios have very different implications for the mass growth of early-type galaxies over the last half of cosmic history.

We present a determination of the distributions of the photon spectral index and gamma-ray flux—the so-called log N–log S relation—for the 352 blazars detected with a greater than approximately 7σ detection threshold and located above ±20° Galactic latitude by the Large Area Telescope of the FermiGamma-ray Space Telescope in its first year catalog. Because the flux detection threshold depends on the photon index, the observed raw distributions do not provide the true log N–log S counts or the true distribution of the photon index. We use the non-parametric methods developed by Efron and Petrosian to reconstruct the intrinsic distributions from the observed ones which account for the data truncations introduced by observational bias and includes the effects of the possible correlation between the two variables. We demonstrate the robustness of our procedures using a simulated data set of blazars and then apply these to the real data and find that for the population as a whole the intrinsic flux distribution can be represented by a broken power law with high and low indices of −2.37 ± 0.13 and −1.70 ± 0.26, respectively, and the intrinsic photon index distribution can be represented by a Gaussian with mean of 2.41 ± 0.13 and width of 0.25 ± 0.03. We also find the intrinsic distributions for the sub-populations of BL Lac and flat spectrum radio quasar type blazars separately. We then calculate the contribution of Fermi blazars to the diffuse extragalactic gamma-ray background radiation. Under the assumption that the flux distribution of blazars continues to arbitrarily low fluxes, we calculate the best-fit contribution of all blazars to the total extragalactic gamma-ray output to be 60%, with a large uncertainty.

We have used high-resolution (∼23) observations of the local (D_L = 46 Mpc) luminous infrared galaxy Arp 299 to map out the physical properties of the molecular gas that provides the fuel for its extreme star formation activity. The ¹²CO J = 3–2, ¹²CO J = 2–1, and ¹³CO J = 2–1 lines were observed with the Submillimeter Array, and the short spacings of the ¹²CO J = 2–1 and J = 3–2 observations have been recovered using the James Clerk Maxwell Telescope single dish observations. We use the radiative transfer code RADEX to estimate the physical properties (density, column density, and temperature) of the different regions in this system. The RADEX solutions of the two galaxy nuclei, IC 694 and NGC 3690, are consistent with a wide range of gas components, from warm moderately dense gas with T_kin > 30 K and n(H₂) ∼ 0.3–3 × 10³ cm⁻³ to cold dense gas with T_kin ∼ 10–30 K and n(H₂) > 3 × 10³ cm⁻³. The overlap region is shown to have a better constrained solution with T_kin ∼ 10–50 K and n(H₂) ∼ 1–30 × 10³ cm⁻³. We estimate the gas masses and star formation rates of each region in order to derive molecular gas depletion times. The depletion times of all regions (20–50 Myr) are found to be about two orders of magnitude lower than those of normal spiral galaxies. This rapid depletion time can probably be explained by a high fraction of dense gas on kiloparsec scales in Arp 299. We estimate the CO-to-H₂ factor, α_co to be 0.4 ± 0.3(3 × 10⁻⁴/x_CO) M_☉ (K km s⁻¹ pc²)⁻¹ for the overlap region. This value agrees well with values determined previously for more advanced merger systems.

We present a study of the cavity system in the galaxy cluster RBS 797 based on Chandra and Very Large Array (VLA) data. RBS 797 (z = 0.35) is one of the most distant galaxy clusters in which two pronounced X-ray cavities have been discovered. The Chandra data confirm the presence of a cool core and indicate a higher metallicity along the cavity directions. This is likely due to the active galactic nucleus outburst, which lifts cool metal-rich gas from the center along the cavities, as seen in other systems. We find indications that the cavities are hotter than the surrounding gas. Moreover, the new Chandra images show bright rims contrasting with the deep, X-ray deficient cavities. The likely cause is that the expanding 1.4 GHz radio lobes have displaced the gas, compressing it into a shell that appears as bright cool arms. Finally, we show that the large-scale radio emission detected with our VLA observations may be classified as a radio mini-halo, powered by the cooling flow, as it nicely follows the trend P_radio versus P_CF predicted by the reacceleration model.

We have previously reported on chemical abundance trends with evolutionary state in the globular cluster NGC 6397 discovered in analyses of spectra taken with FLAMES at the Very Large Telescope. Here, we reinvestigate the FLAMES-UVES sample of 18 stars, ranging from just above the turnoff point to the red giant branch below the bump. Inspired by new calibrations of the infrared flux method, we adopt a set of hotter temperature scales. Chemical abundances are determined for six elements (Li, Mg, Ca, Ti, Cr, and Fe). Signatures of cluster-internal pollution are identified and corrected for in the analysis of Mg. On the modified temperature scales, evolutionary trends in the abundances of Mg and Fe are found to be significant at the 2σ and 3σ levels, respectively. The detailed evolution of abundances for all six elements agrees with theoretical isochrones, calculated with effects of atomic diffusion and a weak to moderately strong efficiency of turbulent mixing. The age of these models is compatible with the external determination from the white dwarf cooling sequence. We find that the abundance analysis cannot be reconciled with the strong turbulent-mixing efficiency inferred elsewhere for halo field stars. A weak mixing efficiency reproduces observations best, indicating a diffusion-corrected primordial lithium abundance of log ε(Li) = 2.57 ± 0.10. At 1.2σ, this value agrees well with Wilkinson Microwave Anisotropy Probe calibrated big bang nucleosynthesis predictions.

We have derived a new expression for the thermohaline mixing coefficient in stars, including the effects of radiative levitation and external turbulence, by solving Boussinesq equations in a nearly incompressible stratified fluid with a linear approximation. It is well known that radiative levitation of individual elements can lead to their accumulation in specific stellar layers. In some cases, it can induce important effects on the stellar structure. Here we confirm that this accumulation is moderated by thermohaline convection due to the resulting inverse μ-gradient. The new coefficient that we have derived shows that the effect of radiative accelerations on the thermohaline instability itself is small. This effect must however be checked in all computations. We also confirm that the presence of large horizontal turbulence can reduce or even suppress the thermohaline convection. These results are important as they concern all the cases of heavy element accumulation in stars. Computations of radiative diffusion must be revisited to include thermohaline convection and its consequences. It may be one of the basic reasons for the fact that the observed abundances are always smaller than those predicted by pure atomic diffusion. In any case, these processes have to compete with rotation-induced mixing, but this competition is more complex than previously thought due to their mutual interaction.

Methanol masers at 6.7 GHz are known to be tracers of high-mass star formation in our Galaxy. In this paper, we study the large-scale physical conditions in the star-forming clumps/cores associated with 6.7 GHz methanol masers using observations of the (1, 1), (2, 2), and (3, 3) inversion transitions of ammonia with the Effelsberg telescope. The gas kinetic temperature is found to be higher than in infrared dark clouds, highlighting the relatively evolved nature of the maser sources. Other than a weak correlation between maser luminosity and the ammonia line width, we do not find any differences between low- and high-luminosity methanol masers.

We are carrying out multi-frequency radio continuum observations, using the Australia Telescope Compact Array, to systematically search for collimated ionized jets toward high-mass young stellar objects (HMYSOs). Here we report observations at 1.4, 2.4, 4.8, and 8.6 GHz, made with angular resolutions of about 7'', 4'', 2'', and 1'', respectively, toward six objects of a sample of 33 southern HMYSOs thought to be in very early stages of evolution. The objects in the sample were selected from radio and infrared catalogs by having positive radio spectral indices and being luminous (L_bol > 2 × 10⁴ L_☉), but underluminous in radio emission compared with that expected from its bolometric luminosity. This criterion makes the radio sources good candidates for being ionized jets. As part of this systematic search, two ionized jets have been discovered: one previously published and the other reported here. The rest of the observed candidates correspond to three hypercompact H ii regions and two ultracompact H ii regions. The two jets discovered are associated with two of the most luminous (7 × 10⁴ and 1.0 × 10⁵ L_☉) HMYSOs known to harbor this type of object, showing that the phenomena of collimated ionized winds appear in the formation process of stars at least up to masses of ∼20 M_☉ and provide strong evidence for a disk-mediated accretion scenario for the formation of high-mass stars. From the incidence of jets in our sample, we estimate that the jet phase in high-mass protostars lasts for ∼4 × 10⁴ yr.

We present the first unambiguous detection of quasi-periodic wave trains within the broad pulse of a global EUV wave (so-called EIT wave) occurring on the limb. These wave trains, running ahead of the lateral coronal mass ejection (CME) front of 2–4 times slower, coherently travel to distances ≳ R_☉/2 along the solar surface, with initial velocities up to 1400 km s⁻¹ decelerating to ∼650 km s⁻¹. The rapid expansion of the CME initiated at an elevated height of 110 Mm produces a strong downward and lateral compression, which may play an important role in driving the primary EUV wave and shaping its front forwardly inclined toward the solar surface. The wave trains have a dominant 2 minute periodicity that matches the X-ray flare pulsations, suggesting a causal connection. The arrival of the leading EUV wave front at increasing distances produces an uninterrupted chain sequence of deflections and/or transverse (likely fast kink mode) oscillations of local structures, including a flux-rope coronal cavity and its embedded filament with delayed onsets consistent with the wave travel time at an elevated (by ∼50%) velocity within it. This suggests that the EUV wave penetrates through a topological separatrix surface into the cavity, unexpected from CME-caused magnetic reconfiguration. These observations, when taken together, provide compelling evidence of the fast-mode MHD wave nature of the primary (outer) fast component of a global EUV wave, running ahead of the secondary (inner) slow component of CME-caused restructuring.

On 2011 May 30, quasi-periodic fast-propagating (QFP) magnetosonic waves accompanied by a C2.8 flare were directly imaged by the Atmospheric Imaging Assembly instrument on board the Solar Dynamics Observatory. The QFP waves successively emanated from the flare kernel, they propagated along a cluster of open coronal loops with a phase speed of ∼834 km s⁻¹ during the flare's rising phase, and the multiple arc-shaped wave trains can be fitted with a series of concentric circles. We generate the k – ω diagram of the Fourier power and find a straight ridge that represents the dispersion relation of the waves. Along the ridge, we find a lot of prominent nodes which represent the available frequencies of the QFP waves. On the other hand, the frequencies of the flare are also obtained by analyzing the flare light curves using the wavelet technique. The results indicate that almost all the main frequencies of the flare are consistent with those of the QFP waves. This suggests that the flare and the QFP waves were possibly excited by a common physical origin. On the other hand, a few low frequencies (e.g., 2.5 mHz (400 s) and 0.7 mHz (1428 s)) revealed by the k – ω diagram cannot be found in the accompanying flare. We propose that these low frequencies were possibly due to the leakage of the pressure-driven p-mode oscillations from the photosphere into the low corona, which should be a noticeable mechanism for driving the QFP waves observed in the corona.

Supernova (SN) explosions enrich the intracluster medium (ICM) both by creating and dispersing metals. We introduce a method to measure the number of SNe and relative contribution of Type Ia supernovae (SNe Ia) and core-collapse supernovae (SNe cc) by directly fitting X-ray spectral observations. The method has been implemented as an XSPEC model called snapec. snapec utilizes a single-temperature thermal plasma code (apec) to model the spectral emission based on metal abundances calculated using the latest SN yields from SN Ia and SN cc explosion models. This approach provides a self-consistent single set of uncertainties on the total number of SN explosions and relative fraction of SN types in the ICM over the cluster lifetime by directly allowing these parameters to be determined by SN yields provided by simulations. We apply our approach to XMM-Newton European Photon Imaging Camera (EPIC), Reflection Grating Spectrometer (RGS), and 200 ks simulated Astro-H observations of a cooling flow cluster, A3112. We find that various sets of SN yields present in the literature produce an acceptable fit to the EPIC and RGS spectra of A3112. We infer that 30.3% ± 5.4% to 37.1% ± 7.1% of the total SN explosions are SNe Ia, and the total number of SN explosions required to create the observed metals is in the range of (1.06 ± 0.34) × 10⁹ to (1.28 ± 0.43) × 10⁹, from snapec fits to RGS spectra. These values may be compared to the enrichment expected based on well-established empirically measured SN rates per star formed. The proportions of SNe Ia and SNe cc inferred to have enriched the ICM in the inner 52 kpc of A3112 is consistent with these specific rates, if one applies a correction for the metals locked up in stars. At the same time, the inferred level of SN enrichment corresponds to a star-to-gas mass ratio that is several times greater than the 10% estimated globally for clusters in the A3112 mass range.

We report multiwavelength observations of the black hole transient GX 339-4 during its outburst decay in 2011 using the data from RXTE, Swift, and SMARTS. Based on the X-ray spectral, temporal, and optical and infrared (OIR) properties, the source evolved from the soft intermediate to the hard state. Twelve days after the start of the transition toward the hard state, a rebrightening was observed simultaneously in the optical and the infrared bands. Spectral energy distributions (SEDs) were created from observations at the start, and close to the peak of the rebrightening. The excess OIR emission above the smooth exponential decay yields flat spectral slopes for these SEDs. Assuming that the excess is from a compact jet, we discuss the possible locations of the spectral break that mark the transition from optically thick to optically thin synchrotron components. Only during the rising part of the rebrightening, we detected fluctuations with the binary period of the system. We discuss a scenario that includes irradiation of the disk in the intermediate state, irradiation of the secondary star during OIR rise, and jet emission dominating during the peak to explain the entire evolution of the OIR light curve.

The massive black hole Sgr A* at the Galactic center is surrounded by a cluster of stars orbiting around it. Light from these stars is bent by the gravitational field of the black hole, giving rise to several phenomena: astrometric displacement of the primary image, the creation of a secondary image that may shift the centroid of Sgr A*, and magnification effects on both images. The soon-to-be second-generation Very Large Telescope Interferometer instrument GRAVITY will perform observations in the near-infrared of the Galactic center at unprecedented resolution, opening the possibility of observing such effects. Here we investigate the observability limits for GRAVITY of gravitational lensing effects on the S-stars in the parameter space 1[D_LS, γ, K], where D_LS is the distance between the lens and the source, γ is the alignment angle of the source, and K is the source's apparent magnitude in the K band. The easiest effect to observe in future years is the astrometric displacement of primary images. In particular, the shift of the star S17 from its Keplerian orbit will be detected as soon as GRAVITY becomes operative. For exceptional configurations, it will be possible to detect effects related to the spin of the black hole or post-Newtonian orders in the deflection.

We have measured electron–ion recombination for Fe xii forming Fe xi using a merged-beam configuration at the heavy-ion storage ring TSR located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. The measured merged-beam recombination rate coefficient (MBRRC) for collision energies from 0 to 1500 eV is presented. This work uses a new method for determining the absolute MBRRC based on a comparison of the ion beam decay rate with and without the electron beam on. For energies below 75 eV, the spectrum is dominated by dielectronic recombination (DR) resonances associated with 3s → 3p and 3p → 3d core excitations. At higher energies, we observe contributions from 3 → N' and 2 → N' core excitation DR. We compare our experimental results to state-of-the-art multi-configuration Breit-Pauli (MCBP) calculations and find significant differences, both in resonance energies and strengths. We have extracted the DR contributions from the measured MBRRC data and transformed them into a plasma recombination rate coefficient (PRRC) for temperatures in the range of 10³–10⁷ K. We show that the previously recommended DR data for Fe xii significantly underestimate the PRRC at temperatures relevant for both photoionized plasmas (PPs) and collisionally ionized plasmas (CPs). This is contrasted with our MCBP PRRC results, which agree with the experiment to within 30% at PP temperatures and even better at CP temperatures. We find this agreement despite the disagreement shown by the detailed comparison between our MCBP and experimental MBRRC results. Last, we present a simple parameterized form of the experimentally derived PRRC for easy use in astrophysical modeling codes.

In order to determine if the material ablated from high-velocity clouds (HVCs) is a significant source of low-velocity high ions (C iv, N v, and O vi) such as those found in the Galactic halo, we simulate the hydrodynamics of the gas and the time-dependent ionization evolution of its carbon, nitrogen, and oxygen ions. Our suite of simulations examines the ablation of warm material from clouds of various sizes, densities, and velocities as they pass through the hot Galactic halo. The ablated material mixes with the environmental gas, producing an intermediate-temperature mixture that is rich in high ions and that slows to the speed of the surrounding gas. We find that the slow mixed material is a significant source of the low-velocity O vi that is observed in the halo, as it can account for at least ∼1/3 of the observed O vi column density. Hence, any complete model of the high ions in the halo should include the contribution to the O vi from ablated HVC material. However, such material is unlikely to be a major source of the observed C iv, presumably because the observed C iv is affected by photoionization, which our models do not include. We discuss a composite model that includes contributions from HVCs, supernova remnants, a cooling Galactic fountain, and photoionization by an external radiation field. By design, this model matches the observed O vi column density. This model can also account for most or all of the observed C iv, but only half of the observed N v.

We present 880 μm images of the transition disk around the star [PZ99] J160421.7-213028, a solar mass star in the nearby Upper Scorpius association. With a resolution down to 034, we resolve the inner hole in this disk, and via model fitting to the visibilities and spectral energy distribution we determine both the structure of the outer region and the presence of sparse dust within the cavity. The disk contains ∼0.1 M_Jup of millimeter-emitting grains, with an inner disk edge of about 70 AU. The inner cavity contains a small amount of dust with a depleted surface density in a region extending from about 20 to 70 AU. Taking into account prior observations indicating little to no stellar accretion, the lack of a binary companion, and the presence of dust near ∼0.1 AU, we determine that the most likely mechanism for the formation of this inner hole is the presence of one or more giant planets.

As the number of discovered extrasolar planets has been increasing, diversity of planetary systems requires studies of new formation scenarios. It is important to study satellite formation in circumplanetary disks, which is often viewed as analogous to formation of rocky planets in protoplanetary disks. We investigated satellite formation from satellitesimals around giant planets through N-body simulations that include gravitational interactions with a circumplanetary gas disk. Our main aim is to reproduce the observable properties of the Galilean satellites around Jupiter through numerical simulations, as previous N-body simulations have not explained the origin of the resonant configuration. We performed accretion simulations based on the work of Sasaki et al., in which an inner cavity is added to the model of Canup & Ward. We found that several satellites are formed and captured in mutual mean motion resonances outside the disk inner edge and are stable after rapid disk gas dissipation, which explains the characteristics of the Galilean satellites. In addition, owing to the existence of the disk edge, a radial compositional gradient of the Galilean satellites can also be reproduced. An additional objective of this study is to discuss orbital properties of formed satellites for a wide range of conditions by considering large uncertainties in model parameters. Through numerical experiments and semianalytical arguments, we determined that if the inner edge of a disk is introduced, a Galilean-like configuration in which several satellites are captured into a 2:1 resonance outside the disk inner cavity is almost universal. In fact, such a configuration is produced even for a massive disk ≳ 10⁴ g cm⁻² and rapid type I migration. This result implies the inevitability of a Galilean satellite formation in addition to providing theoretical predictions for extrasolar satellites. That is, we can predict a substantial number of exomoon systems in the 2:1 mean motion resonance close to their host planets awaiting discovery.

Although accretion onto supermassive black holes in other galaxies is seen to produce powerful jets in X-ray and radio, no convincing detection has ever been made of a kpc-scale jet in the Milky Way. The recently discovered pair of 10 kpc tall gamma-ray bubbles in our Galaxy may be signs of earlier jet activity from the central black hole. In this paper, we identify a gamma-ray cocoon feature in the southern bubble, a jet-like feature along the cocoon's axis of symmetry, and another directly opposite the Galactic center in the north. Both the cocoon and jet-like feature have a hard spectrum with spectral index ∼ − 2 from 1 to 100 GeV, with a cocoon total luminosity of (5.5 ± 0.45) × 10³⁵ and luminosity of the jet-like feature of (1.8 ± 0.35) × 10³⁵ erg s⁻¹ at 1–100 GeV. If confirmed, these jets are the first resolved gamma-ray jets ever seen.

Using H i absorption spectra from the International Galactic Plane Survey, a new method is implemented to resolve the kinematic distance ambiguity for 75 H ii regions with known systemic velocities from radio recombination lines. A further 40 kinematic distance determinations are made for H ii region candidates without known systemic velocities through an investigation of the presence of H i absorption around the terminal velocity. New kinematic distance determinations can be used to further constrain spiral arm parameters and the location and extent of other structures in the Milky Way disk. H i absorption toward continuum sources beyond the solar circle is also investigated. Follow-up studies of H i at higher resolution than the 1' to 2' of existing Galactic Plane Surveys will provide kinematic distances to many more H ii regions on the far side of the Galactic center. On the basis of the velocity channel summation technique developed in this paper, a much larger sample of H ii regions will be analyzed in a future paper to remove the near–far distance ambiguity.

We extend previous measurements of cosmic infrared background (CIB) fluctuations to ≲ 1° using new data from the Spitzer Extended Deep Survey. Two fields with depths of ≃ 12 hr pixel⁻¹ over three epochs are analyzed at 3.6 and 4.5 μm. Maps of the fields were assembled using a self-calibration method uniquely suitable for probing faint diffuse backgrounds. Resolved sources were removed from the maps to a magnitude limit of mag_AB ≃ 25, as indicated by the level of the remaining shot noise. The maps were then Fourier transformed and their power spectra were evaluated. Instrumental noise was estimated from the time-differenced data, and subtracting this isolates the spatial fluctuations of the actual sky. The power spectra of the source-subtracted fields remain identical (within the observational uncertainties) for the three epochs indicating that zodiacal light contributes negligibly to the fluctuations. Comparing to 8 μm power spectra shows that Galactic cirrus cannot account for the fluctuations. The signal appears isotropically distributed on the sky as required for an extragalactic origin. The CIB fluctuations continue to diverge to >10 times those of known galaxy populations on angular scales out to ≲ 1°. The low shot-noise levels remaining in the diffuse maps indicate that the large-scale fluctuations arise from the spatial clustering of faint sources well below the confusion noise. The spatial spectrum of these fluctuations is in reasonable agreement with an origin in populations clustered according to the standard cosmological model (ΛCDM) at epochs coinciding with the first stars era.

We present the abundance analysis of 97 nearby metal-poor (−3.3 < [Fe/H] <−0.5) stars having kinematic characteristics of the Milky Way (MW) thick disk and inner and outer stellar halos. The high-resolution, high-signal-to-noise optical spectra for the sample stars have been obtained with the High Dispersion Spectrograph mounted on the Subaru Telescope. Abundances of Fe, Mg, Si, Ca, and Ti have been derived using a one-dimensional LTE abundance analysis code with Kurucz NEWODF model atmospheres. By assigning membership of the sample stars to the thick disk, inner halo, or outer halo components based on their orbital parameters, we examine abundance ratios as a function of [Fe/H] and kinematics for the three subsamples in wide metallicity and orbital parameter ranges. We show that, in the metallicity range of −1.5 < [Fe/H] ⩽−0.5, the thick disk stars show constantly high mean [Mg/Fe] and [Si/Fe] ratios with small scatter. In contrast, the inner and the outer halo stars show lower mean values of these abundance ratios with larger scatter. The [Mg/Fe], [Si/Fe], and [Ca/Fe] for the inner and the outer halo stars also show weak decreasing trends with [Fe/H] in the range [Fe/H] >−2. These results favor the scenarios that the MW thick disk formed through rapid chemical enrichment primarily through Type II supernovae of massive stars, while the stellar halo has formed at least in part via accretion of progenitor stellar systems having been chemically enriched with different timescales.

We report on the geometry of accretion disk and high-energy coronae in the strong Comptonization state (the very high/steep power law/hard intermediate state) based on a Suzaku observation of the famous Galactic black hole GX 339−4. These data were taken just before the peak of the 2006–2007 outburst, and the average X-ray luminosity in the 0.7–200 keV band is estimated to be 2.9 × 10³⁸ erg s⁻¹ for a distance of 8 kpc. We fit the spectrum with both simple (independent disk and corona) and sophisticated (energetically coupled disk and corona) models; all fits imply that the underlying optically thick disk is truncated significantly before the innermost stable circular orbit around the black hole. We show this directly by a comparison with similar broadband data from a disk-dominated spectrum at almost the same luminosity observed by XMM-Newton and RXTE 3 days after the Suzaku observation. During the Suzaku observation, the quasi-periodic oscillation (QPO) frequency changes from 4.3 Hz to 5.5 Hz, while the spectrum softens. The energetically coupled model gives a corresponding 5% ± 8% decrease in the derived inner radius of the disk. While this is not significant, it is consistent with the predicted change in QPO frequency from the Lense–Thirring precession of the hot flow interior to the disk and/or a deformation mode of this flow, as a higher QPO frequency implies a smaller size scale for the corona. This is consistent with the truncated disk extending further inward toward the black hole.

Motivated by recent discoveries of low-density super-Earths with short orbital periods, we have investigated in situ accretion of H–He atmospheres on rocky bodies embedded in dissipating warm disks, by simulating quasi-static evolution of atmospheres that connect to the ambient disk. We have found that the atmospheric evolution has two distinctly different outcomes, depending on the rocky body's mass: while the atmospheres on massive rocky bodies undergo runaway disk-gas accretion, those on light rocky bodies undergo significant erosion during disk dispersal. In the atmospheric erosion, the heat content of the rocky body that was previously neglected plays an important role. We have also realized that the atmospheric mass is rather sensitive to disk temperature in the mass range of interest in this study. Our theory is applied to recently detected super-Earths orbiting Kepler-11 to examine the possibility that the planets are rock-dominated ones with relatively thick H–He atmospheres. The application suggests that the in situ formation of the relatively thick H–He atmospheres inferred by structure modeling is possible only under restricted conditions, namely, relatively slow disk dissipation and/or cool environments. This study demonstrates that low-density super-Earths provide important clues to understanding of planetary accretion and disk evolution.

We present the spectroscopic and photometric evolution of the nearby (z = 0.059) spectroscopically confirmed Type Ic supernova, SN 2010bh, associated with the soft, long-duration gamma-ray burst (X-ray flash) GRB 100316D. Intensive follow-up observations of SN 2010bh were performed at the ESO Very Large Telescope (VLT) using the X-shooter and FORS2 instruments. Thanks to the detailed temporal coverage and the extended wavelength range (3000–24800 Å), we obtained an unprecedentedly rich spectral sequence among the hypernovae, making SN 2010bh one of the best studied representatives of this SN class. We find that SN 2010bh has a more rapid rise to maximum brightness (8.0 ± 1.0 rest-frame days) and a fainter absolute peak luminosity (L_bol ≈ 3 × 10⁴² erg s⁻¹) than previously observed SN events associated with GRBs. Our estimate of the ejected ⁵⁶Ni mass is 0.12 ± 0.02 M_☉. From the broad spectral features, we measure expansion velocities up to 47,000 km s⁻¹, higher than those of SNe 1998bw (GRB 980425) and 2006aj (GRB 060218). Helium absorption lines He i λ5876 and He i 1.083 μm, blueshifted by ∼20,000–30,000 km s⁻¹ and ∼28,000–38,000 km s⁻¹, respectively, may be present in the optical spectra. However, the lack of coverage of the He i 2.058 μm line prevents us from confirming such identifications. The nebular spectrum, taken at ∼186 days after the explosion, shows a broad but faint [O i] emission at 6340 Å. The light curve shape and photospheric expansion velocities of SN 2010bh suggest that we witnessed a highly energetic explosion with a small ejected mass (E_k ≈ 10⁵² erg and M_ej ≈ 3 M_☉). The observed properties of SN 2010bh further extend the heterogeneity of the class of GRB SNe.

We present seven spectroscopically confirmed Type II cluster supernovae (SNe II) discovered in the Multi-Epoch Nearby Cluster Survey, a supernova survey targeting 57 low-redshift 0.05 < z < 0.15 galaxy clusters with the Canada–France–Hawaii Telescope. We find the rate of Type II supernovae within R₂₀₀ of z ∼ 0.1 galaxy clusters to be 0.026^+0.085_{− 0.018}(stat)^+0.003_{− 0.001}(sys) SNuM. Surprisingly, one SN II is in a red-sequence host galaxy that shows no clear evidence of recent star formation (SF). This is unambiguous evidence in support of ongoing, low-level SF in at least some cluster elliptical galaxies, and illustrates that galaxies that appear to be quiescent cannot be assumed to host only Type Ia SNe. Based on this single SN II we make the first measurement of the SN II rate in red-sequence galaxies, and find it to be 0.007^+0.014_{− 0.007}(stat)^+0.009_{− 0.001}(sys) SNuM. We also make the first derivation of cluster specific star formation rates (sSFR) from cluster SN II rates. We find that for all galaxy types the sSFR is 5.1^+15.8_{− 3.1}(stat) ± 0.9(sys) M_☉ yr⁻¹ (10¹² M_☉)⁻¹, and for red-sequence galaxies only it is 2.0^+4.2_{− 0.9}(stat) ± 0.4(sys) M_☉ yr⁻¹ (10¹² M_☉)⁻¹. These values agree with SFRs measured from infrared and ultraviolet photometry, and Hα emission from optical spectroscopy. Additionally, we use the SFR derived from our SNII rate to show that although a small fraction of cluster Type Ia SNe may originate in the young stellar population and experience a short delay time, these results do not preclude the use of cluster SN Ia rates to derive the late-time delay time distribution for SNe Ia.

Heavy nuclei such as nickel-56 are synthesized in a wide range of core-collapse supernovae (CCSN), including energetic supernovae associated with gamma-ray bursts (GRBs). Recent studies suggest that jet-like outflows are a common feature of CCSN. These outflows may entrain synthesized nuclei at launch or during propagation, and provide interesting multi-messenger signals including heavy ultra-high-energy cosmic rays. Here, we investigate the destruction processes of nuclei during crossing from the stellar material into the jet material via a cocoon, and during propagation after being successfully loaded into the jet. We find that nuclei can survive for a range of jet parameters because collisional cooling is faster than spallation. While canonical high-luminosity GRB jets may contain nuclei, magnetic-dominated models or low-luminosity jets with small bulk Lorentz factors are more favorable for having a significant heavy nuclei component.

We present new Herschel-SPIRE imaging spectroscopy (194–671 μm) of the bright starburst galaxy M82. Covering the CO ladder from J = 4 → 3 to J = 13 → 12, spectra were obtained at multiple positions for a fully sampled ∼3 × 3 arcmin map, including a longer exposure at the central position. We present measurements of ¹²CO, ¹³CO, [C i], [N ii], HCN, and HCO⁺ in emission, along with OH⁺, H₂O⁺, and HF in absorption and H₂O in both emission and absorption, with discussion. We use a radiative transfer code and Bayesian likelihood analysis to model the temperature, density, column density, and filling factor of multiple components of molecular gas traced by ¹²CO and ¹³CO, adding further evidence to the high-J lines tracing a much warmer (∼500 K), less massive component than the low-J lines. The addition of ¹³CO (and [C i]) is new and indicates that [C i] may be tracing different gas than ¹²CO. No temperature/density gradients can be inferred from the map, indicating that the single-pointing spectrum is descriptive of the bulk properties of the galaxy. At such a high temperature, cooling is dominated by molecular hydrogen. Photon-dominated region (PDR) models require higher densities than those indicated by our Bayesian likelihood analysis in order to explain the high-J CO line ratios, though cosmic-ray-enhanced PDR models can do a better job reproducing the emission at lower densities. Shocks and turbulent heating are likely required to explain the bright high-J emission.

We present results from the first application of the Grid of Red Supergiant and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed grid of 80,843 radiative transfer models of evolved stars and circumstellar dust shells composed of either silicate or carbonaceous dust. We fit GRAMS models to ∼30,000 asymptotic giant branch (AGB) and red supergiant (RSG) stars in the LMC, using 12 bands of photometry from the optical to the mid-infrared. Our published data set consists of thousands of evolved stars with individually determined evolutionary parameters such as luminosity and mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate discriminating between oxygen- and carbon-rich chemistry. The global dust injection rate to the interstellar medium (ISM) of the LMC from RSGs and AGB stars is on the order of 2.1 × 10⁻⁵ M_☉ yr⁻¹, equivalent to a total mass injection rate (including the gas) into the ISM of ∼6 × 10⁻³ M_☉ yr⁻¹. Carbon stars inject two and a half times as much dust into the ISM as do O-rich AGB stars, but the same amount of mass. We determine a bolometric correction factor for C-rich AGB stars in the K_s band as a function of J − K_s color, BC$_{K_{s}} = -0.40(J-K_{s})^2 + 1.83(J-K_{s}) + 1.29$. We determine several IR color proxies for the dust mass-loss rate ($\dot{M}_{d}$) from C-rich AGB stars, such as $\log \dot{M_{d}} = ({-18.90}/({(K_{s}-[8.0])+3.37}))-5.93$. We find that a larger fraction of AGB stars exhibiting the "long-secondary period" phenomenon are more O-rich than stars dominated by radial pulsations, and AGB stars without detectable mass loss do not appear on either the first-overtone or fundamental-mode pulsation sequences.

Recent infrared (IR) observations of freshly formed dust in supernova remnants have yielded significantly lower dust masses than predicted by theoretical models and measured from high-redshift observations. The Crab Nebula's pulsar wind is thought to be sweeping up freshly formed supernova (SN) dust along with the ejected gas. The evidence for this dust was found in the form of an IR excess in the integrated spectrum of the Crab and in extinction against the synchrotron nebula that revealed the presence of dust in the filament cores. We present the first spatially resolved emission spectra of dust in the Crab Nebula acquired with the Infrared Spectrograph on board the Spitzer Space Telescope. The IR spectra are dominated by synchrotron emission and show forbidden line emission from S, Si, Ne, Ar, O, Fe, and Ni. We derived a synchrotron spectral map from the 3.6 and 4.5 μm images, and subtracted this contribution from our data to produce a map of the residual continuum emission from dust. The dust emission appears to be concentrated along the ejecta filaments and is well described by an amorphous carbon or silicate grain compositions. We find a dust temperature of 55 ± 4 K for silicates and 60 ± 7 K for carbon grains. The total estimated dust mass is (1.2–12) × 10⁻³ M_☉, well below the theoretical dust yield predicted for a core-collapse supernova. Our grain heating model implies that the dust grain radii are relatively small, unlike what is expected for dust grains formed in a Type IIP SN.

We present and analyze the optical photometric and spectroscopic data of the Be/X-ray binary MXB 0656−072 from 2006 to 2009. A 101.2 day orbital period is found, for the first time, from the present public X-ray data (Swift/BAT and RXTE/ASM). The anti-correlation between the Hα emission and the UBV brightness of MXB 0656−072 during our 2007 observations indicates that a mass ejection event took place in the system. After the mass ejection, a low-density region might develop around the Oe star. With the outward motion of the circumstellar disk, the outer part of the disk interacted with the neutron star around its periastron passage and a series of X-ray outbursts were triggered between MJD 54350 and MJD 54850. The Proportional Counter Array-HEXTE spectra during the 2007–2008 X-ray outbursts could be well fitted by a cutoff power law with low-energy absorption, together with an iron line around 6.4 keV, and a broad cyclotron resonance feature around 30 keV. The same variability of the soft and hard X-ray colors in 2.3–21 keV indicated that there were no overall changes in the spectral shape during the X-ray outbursts, which might only be connected with the changes of the mass accretion rate onto the neutron star.

Through extended integrations using the recently installed deep depletion CCD on the red arm of the Keck I Low Resolution Imaging Spectrograph, we present new measurements of the resolved spectra of 70 morphologically selected star-forming galaxies with i_AB < 24.1 in the redshift range 1 ≲ z < 1.7. Using the formalism introduced in Paper I of this series and available Hubble Space Telescope (HST) Advanced Camera for Surveys images, we successfully recover rotation curves using the extended emission line distribution of [O ii] 3727 Å to 2.2 times the disk scale radius for a sample of 42 galaxies. Combining these measures with stellar masses derived from HST and ground-based near-infrared photometry enables us to construct the stellar mass Tully–Fisher relation (M_*-TFR) in the time interval between the well-constructed relation defined at z ≃ 1 in Paper I and the growing body of resolved dynamics probed with integral field unit spectrographs at z > 2. Remarkably, we find a well-defined TFR with up to 60% increase in scatter and zero-point shift constraint of ΔM_* = 0.02 ± 0.02 dex since z ∼ 1.7, compared to the local relation. Although our sample is incomplete in terms of either a fixed stellar mass or star formation rate limit, we discuss the implications that typical star-forming disk galaxies evolve to arrive on a well-defined TFR within a surprisingly short period of cosmic history.

We present an investigation into the impact of feedback from outflowing UV and X-ray absorbers in nearby (z < 0.04) active galactic nuclei (AGNs). From studies of the kinematics, physical conditions, and variability of the absorbers in the literature, we calculate the possible ranges in the total mass outflow rate ($\dot{M}_{{\rm out}}$) and kinetic luminosity (L_KE) for each AGN, summed over all of its absorbers. These calculations make use of values (or limits) for the radial locations of the absorbers determined from variability, excited-state absorption, and other considerations. From a sample of 10 Seyfert 1 galaxies with detailed photoionization models for their absorbers, we find that 7 have sufficient constraints on the absorber locations to determine $\dot{M}_{{\rm out}}$ and L_KE. For the low-luminosity AGN NGC 4395, these values are low, although we do not have sufficient constraints on the X-ray absorbers to make definitive conclusions. At least five of the six Seyfert 1s with moderate bolometric luminosities (L_bol = 10⁴³ − 10⁴⁵ erg s⁻¹) have mass outflow rates that are 10–1000 times the mass accretion rates needed to generate their observed luminosities, indicating that most of the mass outflow originates from outside the inner accretion disk. Three of these (NGC 4051, NGC 3516, and NGC 3783) have L_KE in the range 0.5%–5% L_bol, which is the range typically required by feedback models for efficient self-regulation of black hole and galactic bulge growth. At least two of the other three (NGC 5548, NGC 4151, and NGC 7469) have L_KE ≳ 0.1%L_bol, although these values may increase if radial locations can be determined for more of the absorbers. We conclude that the outflowing UV and X-ray absorbers in moderate-luminosity AGNs have the potential to deliver significant feedback to their environments.

We analyze Chandra X-ray spectra of the M0 V+M0 V binary GJ 338. As quantified by X-ray surface flux, these are the most inactive M dwarfs ever observed with X-ray grating spectroscopy. We focus on measuring coronal abundances, in particular searching for evidence of abundance anomalies related to first ionization potential (FIP). In the solar corona and wind, low-FIP elements are overabundant, which is the so-called FIP effect. For other stars, particularly very active ones, an "inverse FIP effect" is often observed, with low-FIP elements being underabundant. For both members of the GJ 338 binary, we find evidence for a modest inverse FIP effect, consistent with expectations from a previously reported correlation between spectral type and FIP bias. This amounts to strong evidence that all M dwarfs should exhibit the inverse FIP effect phenomenon, not just the active ones. We take the first step toward modeling the inverse FIP phenomenon in M dwarfs, building on past work that has demonstrated that MHD waves coursing through coronal loops can lead to a ponderomotive force that fractionates elements in a manner consistent with the FIP effect. We demonstrate that in certain circumstances this model can also lead to an inverse FIP effect, pointing the way to more detailed modeling of M dwarf coronal abundances in the future.

We report the discovery by the Swift hard X-ray monitor of the transient source Swift J2058.4+0516 (Sw J2058+05). Our multi-wavelength follow-up campaign uncovered a long-lived (duration ≳ months), luminous X-ray (L_{X, iso} ≈ 3 × 10⁴⁷ erg s⁻¹) and radio (νL_{ν, iso} ≈ 10⁴² erg s⁻¹) counterpart. The associated optical emission, however, from which we measure a redshift of 1.1853, is relatively faint, and this is not due to a large amount of dust extinction in the host galaxy. Based on numerous similarities with the recently discovered GRB 110328A/Swift J164449.3+573451 (Sw J1644+57), we suggest that Sw J2058+05 may be the second member of a new class of relativistic outbursts resulting from the tidal disruption of a star by a supermassive black hole. If so, the relative rarity of these sources (compared with the expected rate of tidal disruptions) implies that either these outflows are extremely narrowly collimated (θ < 1°) or only a small fraction of tidal disruptions generate relativistic ejecta. Analogous to the case of long-duration gamma-ray bursts and core-collapse supernovae, we speculate that rapid spin of the black hole may be a necessary condition to generate the relativistic component. Alternatively, if powered by gas accretion (i.e., an active galactic nucleus (AGN)), Sw J2058+05 would seem to represent a new mode of variability in these sources, as the observed properties appear largely inconsistent with known classes of AGNs capable of generating relativistic jets (blazars, narrow-line Seyfert 1 galaxies).

We present our new deep optical imaging and long-slit spectroscopy for Arp 220, the archetypical ultra luminous infrared galaxy in the local universe. Our sensitive Hα imaging has newly revealed large-scale Hα absorption, i.e., post-starburst regions in this merger. One is found in the eastern superbubble and the other is in the two tidal tails that are clearly revealed in our deep optical imaging. The size of the Hα absorption region in the eastern bubble is 5 kpc × 7.5 kpc, and the observed Hα equivalent widths are ∼2 Å ± 0.2 Å. The sizes of the northern and southern Hα-absorption tidal tails are ∼5 kpc × 10 kpc and ∼6 kpc × 20 kpc, respectively. The observed Hα equivalent widths range from 4 Å to 7 Å. In order to explain the presence of the two post-starburst tails, we suggest a possible multiple-merger scenario for Arp 220 in which two post-starburst disk-like structures merged into one, causing the two tails. This favors Arp 220 as a multiple merging system composed of four or more galaxies arising from a compact group of galaxies. Taking our new results into account, we discuss a star formation history in the last 1 Gyr in Arp 220.

We present a new stellar dynamical mass measurement of the black hole in the nearby, S0 galaxy NGC 3998. By combining laser guide star adaptive optics observations obtained with the OH-Suppressing Infrared Imaging Spectrograph on the Keck II telescope with long-slit spectroscopy from the Hubble Space Telescope and the Keck I telescope, we map out the stellar kinematics on both small spatial scales, well within the black hole sphere of influence, and large scales. We find that the galaxy is rapidly rotating and exhibits a sharp central peak in the velocity dispersion. Using the kinematics and the stellar luminosity density derived from imaging observations, we construct three-integral, orbit-based, triaxial stellar dynamical models. We find the black hole has a mass of M_BH = (8.1^+2.0_−1.9) × 10⁸ M_☉, with an I-band stellar mass-to-light ratio of M/L = 5.0^+0.3_−0.4 M_☉/L_☉ (3σ uncertainties), and that the intrinsic shape of the galaxy is very round, but oblate. With the work presented here, NGC 3998 is now one of a very small number of galaxies for which both stellar and gas dynamical modeling have been used to measure the mass of the black hole. The stellar dynamical mass is nearly a factor of four larger than the previous gas dynamical black hole mass measurement. Given that this cross-check has so far only been attempted on a few galaxies with mixed results, carrying out similar studies in other objects is essential for quantifying the magnitude and distribution of the cosmic scatter in the black hole mass–host galaxy relations.

Ultraviolet observations of the QSO 3C 263 (z_em = 0.652) with Cosmic Origins Spectrograph and FUSE reveal O vi absorption systems at z = 0.06342 and 0.14072. WIYN multi-object spectrograph observations provide information about the galaxies associated with the absorbers. The multi-phase system at z = 0.06342 traces cool photoionized gas and warm collisionally ionized gas associated with an L ∼ 0.31 L* compact spiral emission line galaxy with an impact parameter of 63 kpc. The cool photoionized gas in the absorber is well modeled, with log U ∼ −2.6, log N(H) ∼ 17.8, log n(H) ∼ −3.3 and [Si/H] = −0.14 ± 0.23. The collisionally ionized gas containing C iv and O vi probably arises in cooling shock-heated transition temperature gas with log T ∼ 5.5. The absorber is likely tracing circumgalactic gas enriched by gas ejected from the spiral emission line galaxy. The simple system at z = 0.14072 only contains O vi and broad and narrow H i. The O vi with b = 33.4 ± 11.9 km s⁻¹ is likely associated with the broad H i λ1215 absorption, with b = 86.7 ± 15.4 km s⁻¹. The difference in Doppler parameters implies the detection of a very large column of warm gas with log T = 5.61(+0.16, −0.25), log N(H) = 19.54(+0.26, −0.44), and [O/H] = −1.48 (+0.46, −0.26). This absorber is possibly associated with a 1.6 L* absorption line galaxy with an impact parameter of 617 kpc, although an origin in warm filament gas or in the halo of a fainter galaxy is more likely.

Telescopes aiming to measure 21 cm emission from the Epoch of Reionization must toe a careful line, balancing the need for raw sensitivity against the stringent calibration requirements for removing bright foregrounds. It is unclear what the optimal design is for achieving both of these goals. Via a pedagogical derivation of an interferometer's response to the power spectrum of 21 cm reionization fluctuations, we show that even under optimistic scenarios first-generation arrays will yield low-signal-to-noise detections, and that different compact array configurations can substantially alter sensitivity. We explore the sensitivity gains of array configurations that yield high redundancy in the uv-plane—configurations that have been largely ignored since the advent of self-calibration for high-dynamic-range imaging. We first introduce a mathematical framework to generate optimal minimum-redundancy configurations for imaging. We contrast the sensitivity of such configurations with high-redundancy configurations, finding that high-redundancy configurations can improve power-spectrum sensitivity by more than an order of magnitude. We explore how high-redundancy array configurations can be tuned to various angular scales, enabling array sensitivity to be directed away from regions of the uv-plane (such as the origin) where foregrounds are brighter and instrumental systematics are more problematic. We demonstrate that a 132 antenna deployment of the Precision Array for Probing the Epoch of Reionization observing for 120 days in a high-redundancy configuration will, under ideal conditions, have the requisite sensitivity to detect the power spectrum of the 21 cm signal from reionization at a 3σ level at k < 0.25 h Mpc⁻¹ in a bin of Δln k = 1. We discuss the tradeoffs of low- versus high-redundancy configurations.

The unequivocal, spectroscopic detection of the 2175 Å bump in extinction curves outside the Local Group is rare. To date, the properties of the bump have been examined in only two gamma-ray burst (GRB) afterglows (GRB 070802 and GRB 080607). In this work, we analyze in detail the detections of the 2175 Å extinction bump in the optical spectra of two further GRB afterglows: GRB 080605 and 080805. We gather all available optical/near-infrared photometric, spectroscopic, and X-ray data to construct multi-epoch spectral energy distributions (SEDs) for both GRB afterglows. We fit the SEDs with the Fitzpatrick & Massa model with a single or broken power law. We also fit a sample of 38 GRB afterglows, known to prefer a Small Magellanic Cloud (SMC)-type extinction curve, with the same model. We find that the SEDs of GRB 080605 and GRB 080805 at two epochs are fit well with a single power law with a derived extinction of A_V = 0.52^+0.13_{− 0.16} and 0.50^+0.13_{− 0.10}, and 2.1^+0.7_{− 0.6} and 1.5 ± 0.2, respectively. While the slope of the extinction curve of GRB 080805 is not well constrained, the extinction curve of GRB 080605 has an unusual very steep far-UV rise together with the 2175 Å bump. Such an extinction curve has previously been found in only a small handful of sightlines in the Milky Way. One possible explanation of such an extinction curve may be dust arising from two different regions with two separate grain populations, however we cannot distinguish the origin of the curve. We finally compare the four 2175 Å bump sightlines to the larger GRB afterglow sample and to Local Group sightlines. We find that while the width and central positions of the bumps are consistent with what is observed in the Local Group, the relative strength of the detected bump (A_bump) for GRB afterglows is weaker for a given A_V than for almost any Local Group sightline. Such dilution of the bump strength may offer tentative support to a dual dust-population scenario.

The Fermi Large Area Telescope (LAT) First Source Catalog (1FGL) provided spatial, spectral, and temporal properties for a large number of γ-ray sources using a uniform analysis method. After correlating with the most-complete catalogs of source types known to emit γ rays, 630 of these sources are "unassociated" (i.e., have no obvious counterparts at other wavelengths). Here, we employ two statistical analyses of the primary γ-ray characteristics for these unassociated sources in an effort to correlate their γ-ray properties with the active galactic nucleus (AGN) and pulsar populations in 1FGL. Based on the correlation results, we classify 221 AGN-like and 134 pulsar-like sources in the 1FGL unassociated sources. The results of these source "classifications" appear to match the expected source distributions, especially at high Galactic latitudes. While useful for planning future multiwavelength follow-up observations, these analyses use limited inputs, and their predictions should not be considered equivalent to "probable source classes" for these sources. We discuss multiwavelength results and catalog cross-correlations to date, and provide new source associations for 229 Fermi-LAT sources that had no association listed in the 1FGL catalog. By validating the source classifications against these new associations, we find that the new association matches the predicted source class in ∼80% of the sources.

EXO1745−248 is a transient neutron star low-mass X-ray binary located in the globular cluster Terzan 5. It was in outburst in 2000 and displayed during one Rossi X-ray Timing Explorer observation a highly coherent quasi-periodic oscillation (QPO) at frequencies between 670 and 715 Hz. Applying a maximum likelihood method to fit the X-ray power density spectrum, we show that the QPO can be detected on segments as short as T = 48 s. We find that its width is consistent with being constant, while previous analysis based on longer segment duration (200 s) found it variable. If the QPO frequency variations in EXO1745−248 follow a random walk (i.e., the contribution of the drift to the measured width increases like $\sqrt{T}$), we derive an intrinsic width of ∼2.3 Hz. This corresponds to an intrinsic quality factor of Q ∼ 297 ± 50 at 691 Hz. We also show that Q is consistent with being constant between 2.5 and 25 keV. IGR J17480−2446 is another X-ray transient located in Terzan 5. It is a very interesting object showing accretion-powered pulsations and burst oscillations at 11 Hz. We report on the properties of its kHz QPOs detected between October 18 and October 23, soon after the source had moved from the so-called Atoll state to the Z state. Its QPOs are typical of persistent Z sources; in the sense that they have low Q factors (∼30) and low rms amplitudes (∼5%). The highest frequency (at 870 Hz), if orbital, sets a lower limit on the inner disk radius of ∼18.5 km and an upper limit to the dipole moment of the magnetic field μ ⩽ 5 × 10²⁶ G cm³.

Young star clusters such as NGC 3603 and Westerlund 1 and 2 in the Milky Way and R136 in the Large Magellanic Cloud are dynamically more evolved than expected based on their current relaxation times. In particular, the combination of a high degree of mass segregation, a relatively low central density, and the large number of massive runaway stars in their vicinity are hard to explain with the monolithic formation of these clusters. Young star clusters can achieve such a mature dynamical state if they formed through the mergers of a number of less massive clusters. The shorter relaxation times of less massive clusters cause them to dynamically evolve further by the time they merge, and the merger product preserves the memory of the dynamical evolution of its constituent clusters. With a series of N-body simulations, we study the dynamical evolution of single massive clusters and those that are assembled through merging smaller clusters together. We find that the formation of massive star clusters through the mergers of smaller clusters can reproduce the currently observed spatial distribution of massive stars, the density, and the characteristics (number and mass distribution) of the stars ejected as runaways from young dense clusters. We therefore conclude that these clusters and possibly other young massive star clusters formed through the mergers of smaller clusters.

We have discovered a class of eccentric binary systems within the Kepler data archive that have dynamic tidal distortions and tidally induced pulsations. Each has a uniquely shaped light curve that is characterized by periodic brightening or variability at timescales of 4–20 days, frequently accompanied by shorter period oscillations. We can explain the dominant features of the entire class with orbitally varying tidal forces that occur in close, eccentric binary systems. The large variety of light curve shapes arises from viewing systems at different angles. This hypothesis is supported by spectroscopic radial velocity measurements for five systems, each showing evidence of being in an eccentric binary system. Prior to the discovery of these 17 new systems, only four stars, where KOI-54 is the best example, were known to have evidence of these dynamic tides and tidally induced oscillations. We perform preliminary fits to the light curves and radial velocity data, present the overall properties of this class, and discuss the work required to accurately model these systems.

We consider a numerical model for the shock acceleration of energetic ions in the magnetic environment of the solar corona. The model is motivated by observations of the deka-to-hecto-MeV proton energy spectra, ion and electron timing, and abundances in the beginning of major solar energetic particle (SEP) events, prior to the event's main phase associated with coronal mass ejection (CME) driven shock in the solar wind. Inasmuch as the obliquity of the CME-liftoff-associated shocks in solar corona and hence the seed-particle supply for the shock acceleration are essentially time dependent, a steady state energy spectrum of accelerated protons near the shock could not be attained. Energy spectrum of the SEP emission depends on the spatial and energy distribution of seed particles for the coronal shock acceleration, on the shock wave history, and on the location and scenario of the energetic particle escape into the interplanetary medium. We use a numerical model of the shock acceleration on a semicircular magnetic field line to learn a significance of different effects. If the shock geometry in a particular magnetic tube changes from nearly parallel to perpendicular, the resulting SEP spectrum in most distant sections of the tube, e.g., at the top of a transequatorial loop, resembles a wide beam, which is very different from the standard power-law spectrum that would be expected in a steady state. Possible escape of the shock-accelerated particles from more than one coronal location, stochastic re-acceleration, and the magnetic tube expansion can make the SEP spectra even more complicated.

We investigate the relationship between the main acceleration phase of coronal mass ejections (CMEs) and the particle acceleration in the associated flares as evidenced in Reuven Ramaty High Energy Solar Spectroscopic Imager non-thermal X-rays for a set of 37 impulsive flare-CME events. Both the CME peak velocity and peak acceleration yield distinct correlations with various parameters characterizing the flare-accelerated electron spectra. The highest correlation coefficient is obtained for the relation of the CME peak velocity and the total energy in accelerated electrons (c = 0.85), supporting the idea that the acceleration of the CME and the particle acceleration in the associated flare draw their energy from a common source, probably magnetic reconnection in the current sheet behind the erupting structure. In general, the CME peak velocity shows somewhat higher correlations with the non-thermal flare parameters than the CME peak acceleration, except for the spectral index of the accelerated electron spectrum, which yields a higher correlation with the CME peak acceleration (c ≈ −0.6), indicating that the hardness of the flare-accelerated electron spectrum is tightly coupled to the impulsive acceleration process of the rising CME structure. We also obtained high correlations between the CME initiation height h₀ and the non-thermal flare parameters, with the highest correlation of h₀ to the spectral index δ of flare-accelerated electrons (c ≈ 0.8). This means that CMEs erupting at low coronal heights, i.e., in regions of stronger magnetic fields, are accompanied by flares that are more efficient at accelerating electrons to high energies. In the majority of events (∼80%), the non-thermal flare emission starts after the CME acceleration, on average delayed by ≈6 minutes, in line with the standard flare model where the rising flux rope stretches the field lines underneath until magnetic reconnection sets in. We find that the current sheet length at the onset of magnetic reconnection is 21 ± 7 Mm. The flare hard X-ray peaks are well synchronized with the peak of the CME acceleration profile, and in 75% of the cases they occur within ±5 minutes. Our findings provide strong evidence for the tight coupling between the CME dynamics and the particle acceleration in the associated flare in impulsive events, with the total energy in accelerated electrons being closely correlated with the peak velocity (and thus the kinetic energy) of the CME, whereas the number of electrons accelerated to high energies is decisively related to the CME peak acceleration and the height of the pre-eruptive structure.

The formation and the temporal evolution of a bipolar moving magnetic feature (MMF) was studied with high-spatial and temporal resolution. The photometric properties were observed with the New Solar Telescope at Big Bear Solar Observatory using a broadband TiO filter (705.7 nm), while the magnetic field was analyzed using the spectropolarimetric data obtained by Hinode. For the first time, we observed a bipolar MMF simultaneously in intensity images and magnetic field data, and studied the details of its structure. The vector magnetic field and the Doppler velocity of the MMF were also studied. A bipolar MMF with its positive polarity closer to the negative penumbra formed, accompanied by a bright, filamentary structure in the TiO data connecting the MMF and a dark penumbral filament. A fast downflow (⩽2 km s⁻¹) was detected at the positive polarity. The vector magnetic field obtained from the full Stokes inversion revealed that a bipolar MMF has a U-shaped magnetic field configuration. Our observations provide a clear intensity counterpart of the observed MMF in the photosphere, and strong evidence of the connection between the MMF and the penumbral filament as a serpentine field.

We estimate the stellar parameters of late K- and early M-type Kepler target stars. We obtain medium-resolution visible spectra of 382 stars with K_P − J > 2 (≃K5 and later spectral type). We determine luminosity class by comparing the strength of gravity-sensitive indices (CaH, K i, Ca ii, and Na i) to their strength in a sample of stars of known luminosity class. We find that giants constitute 96% ± 1% of the bright (K_P < 14) Kepler target stars, and 7% ± 3% of dim (K_P > 14) stars, significantly higher than fractions based on the stellar parameters quoted in the Kepler Input Catalog (KIC). The KIC effective temperatures are systematically (110⁺¹⁵_{− 35} K) higher than temperatures we determine from fitting our spectra to PHOENIX stellar models. Through Monte Carlo simulations of the Kepler exoplanet candidate population, we find a planet occurrence of 0.36 ± 0.08 when giant stars are properly removed, somewhat higher than when a KIC log g > 4 criterion is used (0.27 ± 0.05). Last, we show that there is no significant difference in g − r color (a probe of metallicity) between late-type Kepler stars with transiting Earth-to-Neptune-size exoplanet candidates and dwarf stars with no detected transits. We show that a previous claimed offset between these two populations is most likely an artifact of including a large number of misidentified giants.

Many planets are observed in stellar binary systems, and their frequency may be comparable to that of planetary systems around single stars. Binary stellar evolution in such systems influences the dynamical evolution of the resident planets. Here, we study the evolution of a single planet orbiting one star in an evolving binary system. We find that stellar evolution can trigger dynamical instabilities that drive planets into chaotic orbits. This instability leads to planet–star collisions, exchange of the planet between the binary stars ("star hoppers"), and ejection of the planet from the system. The means by which planets can be recaptured is similar to the pull-down capture mechanism for irregular solar system satellites. Because planets often suffer close encounters with the primary on the asymptotic giant branch, captures during a collision with the stellar envelope are also possible for more massive planets. Such capture could populate the habitable zone around white dwarfs.