Table of contents

One of the central goals of multi-wavelength galaxy cluster cosmology is to unite all cluster observables to form a consistent understanding of cluster mass. Here, we study the impact of systematic effects from optical cluster catalogs on stacked Sunyaev–Zel'dovich (SZ) signals. We show that the optically predicted Y-decrement can vary by as much as 50% based on the current 2σ systematic uncertainties in the observed mass–richness relationship. Miscentering and impurities will suppress the SZ signal compared to expectations for a clean and perfectly centered optical sample, but to a lesser degree. We show that the levels of these variations and suppression are dependent on the amount of systematics in the optical cluster catalogs. We also study X-ray luminosity-dependent sub-sampling of the optical catalog and find that it creates Malmquist bias, increasing the observed Y-decrement of the stacked signal. We show that the current Planck measurements of the Y-decrement around Sloan Digital Sky Survey optical clusters and their X-ray counterparts are consistent with expectations after accounting for the 1σ optical systematic uncertainties using the Johnston mass–richness relation.

Locating the centers of dark matter halos is critical for understanding the mass profiles of halos, as well as the formation and evolution of the massive galaxies that they host. The task is observationally challenging because we cannot observe halos directly, and tracers such as bright galaxies or X-ray emission from hot plasma are imperfect. In this paper, we quantify the consequences of miscentering on the weak lensing signal from a sample of 129 X-ray-selected galaxy groups in the COSMOS field with redshifts 0 < z < 1 and halo masses in the range 10¹³–10¹⁴ M_☉. By measuring the stacked lensing signal around eight different candidate centers (such as the brightest member galaxy, the mean position of all member galaxies, or the X-ray centroid), we determine which candidates best trace the center of mass in halos. In this sample of groups, we find that massive galaxies near the X-ray centroids trace the center of mass to ≲ 75 kpc, while the X-ray position and centroids based on the mean position of member galaxies have larger offsets primarily due to the statistical uncertainties in their positions (typically ∼50–150 kpc). Approximately 30% of groups in our sample have ambiguous centers with multiple bright or massive galaxies, and some of these groups show disturbed mass profiles that are not well fit by standard models, suggesting that they are merging systems. We find that halo mass estimates from stacked weak lensing can be biased low by 5%–30% if inaccurate centers are used and the issue of miscentering is not addressed.

We present an X-ray stacking analysis of a sample of 38 submillimeter galaxies (SMGs) with 〈z〉 = 2.6 discovered at ⩾4σ significance in the Lockman Hole North with the MAMBO array. We find a 5σ detection in the stacked soft band (0.5–2.0 keV) image, and no significant detection in the hard band (2.0–8 keV). We also perform rest-frame spectral stacking based on spectroscopic and photometric redshifts and find a ∼4σ detection of Fe Kα emission with an equivalent width of EW ≳ 1 keV. The centroid of the Fe Kα emission lies near 6.7 keV, indicating a possible contribution from highly ionized Fe xxv or Fe xxvi; there is also a slight indication that the line emission is more spatially extended than the X-ray continuum. This is the first X-ray analysis of a complete, flux-limited sample of SMGs with statistically robust radio counterparts.

We extend the phenomenological study of the evolving galaxy population of Peng et al. (2010) to the central/satellite dichotomy in Yang et al. Sloan Digital Sky Survey (SDSS) groups. We find that satellite galaxies are responsible for all the environmental effects in our earlier work. The fraction of centrals that are red does not depend on their environment but only on their stellar masses, whereas that of the satellites depends on both. We define a relative satellite quenching efficiency ε_sat, which is the fraction of blue centrals that are quenched upon becoming the satellite of another galaxy. This is shown to be independent of stellar mass, but to depend strongly on local overdensity, δ, ranging between 0.2 and at least 0.8. The red fraction of satellites correlate much better with the local overdensity δ, a measure of location within the group, than with the richness of the group, i.e., dark matter halo mass. This, and the fact that satellite quenching depends on local density and not on either the stellar mass of the galaxy or the dark matter halo mass, gives clues as to the nature of the satellite-quenching process. We furthermore show that the action of mass quenching on satellite galaxies is also independent of the dark matter mass of the parent halo. We then apply the Peng et al. approach to predict the mass functions of central and satellite galaxies, split into passive and active galaxies, and show that these match very well the observed mass functions from SDSS, further strengthening the validity of this phenomenological approach. We highlight the fact that the observed M* is exactly the same for the star-forming centrals and satellites and the observed M* for the star-forming satellites is independent of halo mass above 10¹² M_☉, which emphasizes the universality of the mass-quenching process that we identified in Peng et al. Post-quenching merging modifies the mass function of the central galaxies but can increase the mass of typical centrals by only about 25%.

Close-in exoplanets with highly eccentric orbits are subject to large variations in incoming stellar flux between periapse and apoapse. These variations may lead to large swings in atmospheric temperature, which in turn may cause changes in the chemistry of the atmosphere from higher CO abundances at periapse to higher CH₄ abundances at apoapse. Here, we examine chemical timescales for CO$\rightleftarrows$CH₄ interconversion compared to orbital timescales and vertical mixing timescales for the highly eccentric exoplanets HAT-P-2b and CoRoT-10b. As exoplanet atmospheres cool, the chemical timescales for CO$\rightleftarrows$CH₄ tend to exceed orbital and/or vertical mixing timescales, leading to quenching. The relative roles of orbit-induced thermal quenching and vertical quenching depend upon mixing timescales relative to orbital timescales. For both HAT-P-2b and CoRoT-10b, vertical quenching will determine disequilibrium CO$\rightleftarrows$CH₄ chemistry at faster vertical mixing rates (K_zz > 10⁷ cm² s⁻¹), whereas orbit-induced thermal quenching may play a significant role at slower mixing rates (K_zz < 10⁷ cm² s⁻¹). The general abundance and chemical timescale results—calculated as a function of pressure, temperature, and metallicity—can be applied for different atmospheric profiles in order to estimate the quench level and disequilibrium abundances of CO and CH₄ on hydrogen-dominated exoplanets. Observations of CO and CH₄ on highly eccentric exoplanets may yield important clues to the chemical and dynamical properties of their atmospheres.

We present a new empirical calibration of equilibrium tidal theory for extrasolar planet systems, extending a prior study by incorporating detailed physical models for the internal structure of planets and host stars. The resulting strength of the stellar tide produces a coupling that is strong enough to reorient the spins of some host stars without causing catastrophic orbital evolution, thereby potentially explaining the observed trend in alignment between stellar spin and planetary orbital angular momentum. By isolating the sample whose spins should not have been altered in this model, we also show evidence for two different processes that contribute to the population of planets with short orbital periods. We apply our results to estimate the remaining lifetimes for short-period planets, examine the survival of planets around evolving stars, and determine the limits for circularization of planets with highly eccentric orbits. Our analysis suggests that the survival of circularized planets is strongly affected by the amount of heat dissipated, which is often large enough to lead to runaway orbital inflation and Roche lobe overflow.

We use data from the Wide-field Infrared Survey Explorer (WISE) all-sky release to explore the incidence of warm dust in the habitable zones around exoplanet-host stars. Dust emission at 12 and/or 22 μm (T_dust ∼ 300 and/or ∼150 K) traces events in the terrestrial planet zones; its existence implies replenishment by evaporation of comets or collisions of asteroids, possibly stirred by larger planets. Of the 591 planetary systems (728 extrasolar planets) in the Exoplanet Encyclopaedia as of 2012 January 31, 350 are robustly detected by WISE at ⩾5σ level. We perform detailed photosphere subtraction using tools developed for Spitzer data and visually inspect all the WISE images to confirm bona fide point sources. We find nine planet-bearing stars show dust excess emission at 12 and/or 22 μm at ⩾3σ level around young, main-sequence, or evolved giant stars. Overall, our results yield an excess incidence of ∼2.6% for stars of all evolutionary stages, but ∼1% for planetary debris disks around main-sequence stars. Besides recovering previously known warm systems, we identify one new excess candidate around the young star UScoCTIO 108.

We present a new computational approach to the inversion of solar photospheric Stokes polarization profiles, under the Milne–Eddington model, for vector magnetography. Our code, named GENESIS, employs multi-threaded parallel-processing techniques to harness the computing power of graphics processing units (GPUs), along with algorithms designed to exploit the inherent parallelism of the Stokes inversion problem. Using a genetic algorithm (GA) engineered specifically for use with a GPU, we produce full-disk maps of the photospheric vector magnetic field from polarized spectral line observations recorded by the Synoptic Optical Long-term Investigations of the Sun (SOLIS) Vector Spectromagnetograph (VSM) instrument. We show the advantages of pairing a population-parallel GA with data-parallel GPU-computing techniques, and present an overview of the Stokes inversion problem, including a description of our adaptation to the GPU-computing paradigm. Full-disk vector magnetograms derived by this method are shown using SOLIS/VSM data observed on 2008 March 28 at 15:45 UT.

The size, mass, luminosity, and space density of Lyα emitting (LAE) galaxies observed at intermediate to high redshift agree with expectations for the properties of galaxies that formed metal-poor halo globular clusters (GCs). The low metallicity of these clusters is the result of their formation in low-mass galaxies. Metal-poor GCs could enter spiral galaxies along with their dwarf galaxy hosts, unlike metal-rich GCs, which form in the spirals themselves. Considering an initial GC mass larger than the current mass to account for multiple stellar populations, and considering the additional clusters that are likely to form with massive clusters, we estimate that each GC with a mass today greater than 2 × 10⁵ M_☉ was likely to have formed among a total stellar mass ≳ 3 × 10⁷ M_☉, a molecular mass ≳ 10⁹ M_☉, and 10⁷ to 10⁹ M_☉ of older stars, depending on the relative gas fraction. The star formation rate would have been several M_☉ yr⁻¹ lasting for ∼10⁷ yr, and the Lyα luminosity would have been ≳ 10⁴² erg s⁻¹. Integrating the LAE galaxy luminosity function above this minimum, considering the average escape probability for Lyα photons (25%), and then dividing by the probability that a dwarf galaxy is observed in the LAE phase (0.4%), we find agreement between the comoving space density of LAEs and the average space density of metal-poor GCs today. The local galaxy WLM, with its early starburst and old GC, could be an LAE remnant that did not get into a galaxy halo because of its remote location.

We present optical spectroscopic measurements of the eclipsing high-mass X-ray binary (HMXB) XMMU J013236.7+303228 in M 33. Based on spectra taken at multiple epochs of the 1.73 day binary orbital period we determine physical as well as orbital parameters for the donor star. We find the donor to be a B1.5IV subgiant with effective temperature T = 22, 000–23, 000 K. From the luminosity, temperature, and known distance to M 33 we derive a radius of R = 8.9 ± 0.5 R_☉. From the radial-velocity measurements, we determine a velocity semi-amplitude of K_opt = 63 ± 12 km s⁻¹. Using the physical properties of the B star determined from the optical spectrum, we estimate the star's mass to be M_opt = 11 ± 1 M_☉. Based on the X-ray spectrum, the compact companion is likely a neutron star, although no pulsations have yet been detected. Using the spectroscopically derived B star mass we find the neutron star companion mass to be M_X = 2.0 ± 0.4 M_☉, consistent with the neutron star mass in the HMXB Vela X-1, but heavier than the canonical value of 1.4 M_☉ found for many millisecond pulsars. We attempt to use as an additional constraint that the B star radius inferred from temperature, flux, and distance should equate to the Roche radius, since the system accretes by Roche lobe overflow. This leads to substantially larger masses, but by trying to apply the technique to known systems, we find that the masses are consistently overestimated. Attempting to account for that in our uncertainties, we derive M_X = 2.2^+0.8_{− 0.6} M_☉ and M_opt = 13 ± 4 M_☉. We conclude that precise constraints require detailed modeling of the shape of the Roche surface.

Models of jet production in black hole systems suggest that the properties of the accretion disk—such as its mass accretion rate, inner radius, and emergent magnetic field—should drive and modulate the production of relativistic jets. Stellar-mass black holes in the "low/hard" state are an excellent laboratory in which to study disk–jet connections, but few coordinated observations are made using spectrometers that can incisively probe the inner disk. We report on a series of 20 Suzaku observations of Cygnus X-1 made in the jet-producing low/hard state. Contemporaneous radio monitoring was done using the Arcminute MicroKelvin Array radio telescope. Two important and simple results are obtained: (1) the jet (as traced by radio flux) does not appear to be modulated by changes in the inner radius of the accretion disk and (2) the jet is sensitive to disk properties, including its flux, temperature, and ionization. Some more complex results may reveal aspects of a coupled disk–corona–jet system. A positive correlation between the reflected X-ray flux and radio flux may represent specific support for a plasma ejection model of the corona, wherein the base of a jet produces hard X-ray emission. Within the framework of the plasma ejection model, the spectra suggest a jet base with v/c ≃ 0.3 or the escape velocity for a vertical height of z ≃ 20 GM/c² above the black hole. The detailed results of X-ray disk continuum and reflection modeling also suggest a height of z ≃ 20 GM/c² for hard X-ray production above a black hole, with a spin in the range 0.6 ⩽ a ⩽ 0.99. This height agrees with X-ray time lags recently found in Cygnus X-1. The overall picture that emerges from this study is broadly consistent with some jet-focused models for black hole spectral energy distributions in which a relativistic plasma is accelerated at z = 10–100 GM/c². We discuss these results in the context of disk–jet connections across the black hole mass scale.

We present optical photometry and spectroscopy of five Type Ia supernovae discovered by the Nearby Supernova Factory selected to be spectroscopic analogs of the candidate super-Chandrasekhar-mass events SN 2003fg and SN 2007if. Their spectra are characterized by hot, highly ionized photospheres near maximum light, for which SN 1991T supplies the best phase coverage among available close spectral templates. Like SN 2007if, these supernovae are overluminous (−19.5 < M_V < −20) and the velocity of the Si ii λ6355 absorption minimum is consistent with being constant in time from phases as early as a week before, and up to two weeks after, B-band maximum light. We interpret the velocity plateaus as evidence for a reverse-shock shell in the ejecta formed by interaction at early times with a compact envelope of surrounding material, as might be expected for SNe resulting from the mergers of two white dwarfs. We use the bolometric light curves and line velocity evolution of these SNe to estimate important parameters of the progenitor systems, including ⁵⁶Ni mass, total progenitor mass, and masses of shells and surrounding carbon/oxygen envelopes. We find that the reconstructed total progenitor mass distribution of the events (including SN 2007if) is bounded from below by the Chandrasekhar mass, with SN 2007if being the most massive. We discuss the relationship of these events to the emerging class of super-Chandrasekhar-mass SNe Ia, estimate the relative rates, compare the mass distribution to that expected for double-degenerate SN Ia progenitors from population synthesis, and consider implications for future cosmological Hubble diagrams.

In this paper, we characterize the infrared spectral energy distributions (SEDs) of mid-IR-selected z ∼ 0.3–3.0 and L_IR ∼ 10¹¹–10¹³ L_☉ galaxies, and study how their SEDs differ from those of local and high-z analogs. Infrared SEDs depend both on the power source (AGN or star formation) and the dust distribution. Therefore, differences in the SEDs of high-z and local galaxies provide clues as to differences in their physical conditions. Our mid-IR flux-limited sample of 191 sources is unique in size, and spectral coverage, including Spitzer mid-IR spectroscopy. Here, we add Herschel photometry at 250 μm, 350 μm, and 500 μm, which allows us, through fitting an empirical SED model, to obtain accurate total IR luminosities, as well as constrain the relative contributions of AGNs and starbursts to those luminosities. Our sample includes three broad categories of SEDs: ∼23% of the sources are AGNs (i.e., where the AGN contributes >50% of L_IR), ∼30% are starbursts where an AGN contributes <20% of L_IR, and the mid-IR spectra are starburst-like (i.e., strong polycyclic aromatic hydrocarbon features); and the largest group (∼47%) are composites which show both significant AGN and starburst activity. The AGN-dominated sources divide into ones that show a strong silicate 9.7 μm absorption feature, implying highly obscured systems, and ones that do not. The high-τ_9.7 sources are half of our z > 1.2 AGNs, but show SEDs that are extremely rare among local AGNs. The 30% of the sample that are starbursts, even the z ∼ 2, L_IR ∼ 10¹³ L_☉ ones, have lower far-IR to mid-IR continuum ratios than local Ultra Luminous Infrared Galaxies (ULIRGs) or the z ∼ 2 sub-mm galaxies—effectively the SEDs of our z ∼ 2 starburst-dominated ULIRGs are much closer to those of local Luminous Infrared Galaxies than ULIRGs. This is consistent with our earlier finding that, unlike local ULIRGs, our high-z starbursts are typically only in the early stages of a merger. The SEDs of the composite sources are most similar to the local archetypal warm ULIRG, Mrk231, which supports the interpretation of their consisting of both AGN and starburst components. In summary, our results show that there is strong evolution in the SEDs between local and z ∼ 2 IR-luminous galaxies, as well as that there is a wide range of SEDs among high redshift IR-luminous sources. The publicly available SED templates we derive from our sample will be particularly useful for infrared population synthesis models, as well as in the interpretation of other mid-IR high-z galaxies, in particular those detected by the recent all sky Wide-field Infrared Survey Explorer.

A new, much-improved model of the Galactic magnetic field (GMF) is presented. We use the WMAP7 Galactic synchrotron emission map and more than 40,000 extragalactic rotation measures to constrain the parameters of the GMF model, which is substantially generalized compared with earlier work to now include an out-of-plane component (as suggested by observations of external galaxies) and striated-random fields (motivated by theoretical considerations). The new model provides a greatly improved fit to observations. Consistent with our earlier analyses, the best-fit model has a disk field and an extended halo field. Our new analysis reveals the presence of a large, out-of-plane component of the GMF; as a result, the polarized synchrotron emission of our Galaxy seen by an edge-on observer is predicted to look intriguingly similar to what has been observed in external edge-on galaxies. We find evidence that the cosmic-ray electron density is significantly larger than given by GALPROP or else that there is a widespread striated component to the GMF.

We report a discovery of a proto-cluster in vigorous assembly and hosting strong star-forming activities, associated with a radio galaxy USS 1558-003 at z = 2.53, as traced by wide-field narrow-band Hα imaging with MOIRCS on the Subaru Telescope. We find 68 Hα emitters with dust-uncorrected star formation rates (SFRs) down to 8.6 M_☉ yr⁻¹. Their spatial distribution indicates that there are three prominent clumps of Hα emitters: one surrounding the radio galaxy, the second located at ∼1.5 Mpc away to the southwest, and the third located between the two. These contiguous three systems are very likely to merge together in the near future and may grow to a single more massive cluster at a later time. While most Hα emitters reside in the "blue cloud" on the color–magnitude diagram, some emitters have very red colors with J − K_s > 1.38(AB). Interestingly, such red Hα emitters are located toward the faint end of the red sequence, and they tend to be located in high density clumps. We do not see any statistically significant difference in the distributions of individual SFRs or stellar masses of the Hα emitters between the dense clumps and the other regions, suggesting that this is one of the notable sites where the progenitors of massive galaxies in the present-day clusters were in their vigorous formation phase. Finally, we find that Hα emission of the radio galaxy is fairly extended spatially over ∼45. However, it is not as widespread as its Lyα halo, meaning that the Lyα emission is indeed severely extended by resonant scattering.

We have investigated the influence of jet rotation and differential motion on the linear and nonlinear development of the current-driven (CD) kink instability of force-free helical magnetic equilibria via three-dimensional relativistic magnetohydrodynamic simulations. In this study, we follow the temporal development within a periodic computational box. Displacement of the initial helical magnetic field leads to the growth of the CD kink instability. We find that, in accordance with the linear stability theory, the development of the instability depends on the lateral distribution of the poloidal magnetic field. If the poloidal field significantly decreases outward from the axis, then the initial small perturbations grow strongly, and if multiple wavelengths are excited, then nonlinear interaction eventually disrupts the initial cylindrical configuration. When the profile of the poloidal field is shallow, the instability develops slowly and eventually saturates. We briefly discuss implications of our findings for Poynting-dominated jets.

We use high-resolution spectral emission line data obtained by the SERTS instrument during three rocket flights to demonstrate a new approach for constraining electron densities of solar active region plasma. We apply differential emission measure (DEM) forward-fitting techniques to characterize the multithermal solar plasma producing the observed EUV spectra, with constraints on the high-temperature plasma from the Yohkoh Soft X-ray Telescope. In this iterative process, we compare line intensities predicted by an input source distribution to observed line intensities for multiple iron ion species, and search a broad range of densities to optimize χ² simultaneously for the many available density-sensitive lines. This produces a density weighted by the DEM, which appears to be useful for characterizing the bulk of the emitting plasma over a significant range of temperature. This "DEM-weighted density" technique is complementary to the use of density-sensitive line ratios and less affected by uncertainties in atomic data and ionization fraction for any specific line. Once the DEM shape and the DEM-weighted density have been established from the iron lines, the relative elemental abundances can be determined for other lines in the spectrum. We have also identified spectral lines in the SERTS wavelength range that may be problematic.

We provide evidence that the obliquities of stars with close-in giant planets were initially nearly random, and that the low obliquities that are often observed are a consequence of star–planet tidal interactions. The evidence is based on 14 new measurements of the Rossiter–McLaughlin effect (for the systems HAT-P-6, HAT-P-7, HAT-P-16, HAT-P-24, HAT-P-32, HAT-P-34, WASP-12, WASP-16, WASP-18, WASP-19, WASP-26, WASP-31, Gl 436, and Kepler-8), as well as a critical review of previous observations. The low-obliquity (well-aligned) systems are those for which the expected tidal timescale is short, and likewise the high-obliquity (misaligned and retrograde) systems are those for which the expected timescale is long. At face value, this finding indicates that the origin of hot Jupiters involves dynamical interactions like planet–planet interactions or the Kozai effect that tilt their orbits rather than inspiraling due to interaction with a protoplanetary disk. We discuss the status of this hypothesis and the observations that are needed for a more definitive conclusion.

This paper investigates the distribution of linear polarization signals in the quiet-Sun internetwork using ultra-deep spectropolarimetric data. We reduce the noise of the observations as much as is feasible by adding single-slit measurements of the Zeeman-sensitive Fe i 630 nm lines taken by the Hinode spectropolarimeter. The integrated Stokes spectra are employed to determine the fraction of the field of view covered by linear polarization signals. We find that up to 69% of the quiet solar surface at disk center shows Stokes Q or U profiles with amplitudes larger than 0.032% (4.5 times the noise level of 7 × 10⁻⁵ reached by the longer integrations). The mere presence of linear polarization in most of the quiet Sun implies that the weak internetwork fields must be highly inclined, but we quantify this by inverting those pixels with Stokes Q or U signals well above the noise. This allows for a precise determination of the field inclination, field strength, and field azimuth because the information carried by all four Stokes spectra is used simultaneously. The inversion is performed for 53% of the observed field of view at a noise level of 1.3 × 10⁻⁴ I_c. The derived magnetic distributions are thus representative of more than half of the quiet-Sun internetwork. Our results confirm the conclusions drawn from previous analyses using mainly Stokes I and V: internetwork fields are very inclined, but except in azimuth they do not seem to be isotropically distributed.

During flares and coronal mass ejections, energetic electrons from coronal sources typically have very long lifetimes compared to the transit times across the systems, suggesting confinement in the source region. Particle-in-cell simulations are carried out to explore the mechanisms of energetic electron transport from the corona to the chromosphere and possible confinement. We set up an initial system of pre-accelerated hot electrons in contact with ambient cold electrons along the local magnetic field and let it evolve over time. Suppression of transport by a nonlinear, highly localized electrostatic electric field (in the form of a double layer) is observed after a short phase of free-streaming by hot electrons. The double layer (DL) emerges at the contact of the two electron populations. It is driven by an ion–electron streaming instability due to the drift of the back-streaming return current electrons interacting with the ions. The DL grows over time and supports a significant drop in temperature and hence reduces heat flux between the two regions that is sustained for the duration of the simulation. This study shows that transport suppression begins when the energetic electrons start to propagate away from a coronal acceleration site. It also implies confinement of energetic electrons with kinetic energies less than the electrostatic energy of the DL for the DL lifetime, which is much longer than the electron transit time through the source region.

This second paper of the series investigates the transverse response of a magnetic field to the independent relaxation of its flux tubes of fluid seeking hydrostatic and energy balance, under the frozen-in condition and suppression of cross-field thermal conduction. The temperature, density, and pressure naturally develop discontinuities across the magnetic flux surfaces separating the tubes, requiring the finite pressure jumps to be compensated by magnetic-pressure jumps in cross-field force balance. The tangentially discontinuous fields are due to discrete currents in these surfaces, δ-function singularities in the current density that are fully admissible under the rigorous frozen-in condition but must dissipate resistively if the electrical conductivity is high but finite. The magnetic field and fluid must thus endlessly evolve by this spontaneous formation and resistive dissipation of discrete currents taking place intermittently in spacetime, even in a low-β environment. This is a multi-dimensional effect in which the field plays a central role suppressed in the one-dimensional (1D) slab model of the first paper. The study begins with an order-of-magnitude demonstration that of the weak resistive and cross-field thermal diffusivities in the corona, the latter is significantly weaker for small β. This case for spontaneous discrete currents, as an important example of the general theory of Parker, is illustrated with an analysis of singularity formation in three families of two-dimensional generalizations of the 1D slab model. The physical picture emerging completes the hypothesis formulated in Paper I that this intermittent process is the origin of the dynamic interiors of a class of quiescent prominences revealed by recent Hinode/SOT and SDO/AIA high-resolution observations.

We precisely constrain the inner mass profile of A2261 (z = 0.225) for the first time and determine that this cluster is not "overconcentrated" as found previously, implying a formation time in agreement with ΛCDM expectations. These results are based on multiple strong-lensing analyses of new 16-band Hubble Space Telescope imaging obtained as part of the Cluster Lensing and Supernova survey with Hubble. Combining this with revised weak-lensing analyses of Subaru wide-field imaging with five-band Subaru + KPNO photometry, we place tight new constraints on the halo virial mass M_vir = (2.2 ± 0.2) × 10¹⁵ M_☉ h⁻¹₇₀ (within r_vir ≈ 3 Mpc h⁻¹₇₀) and concentration c_vir = 6.2 ± 0.3 when assuming a spherical halo. This agrees broadly with average c(M, z) predictions from recent ΛCDM simulations, which span 5 ≲ 〈c〉 ≲ 8. Our most significant systematic uncertainty is halo elongation along the line of sight (LOS). To estimate this, we also derive a mass profile based on archival Chandra X-ray observations and find it to be ∼35% lower than our lensing-derived profile at r₂₅₀₀ ∼ 600 kpc. Agreement can be achieved by a halo elongated with a ∼2:1 axis ratio along our LOS. For this elongated halo model, we find M_vir = (1.7 ± 0.2) × 10¹⁵ M_☉ h⁻¹₇₀ and c_vir = 4.6 ± 0.2, placing rough lower limits on these values. The need for halo elongation can be partially obviated by non-thermal pressure support and, perhaps entirely, by systematic errors in the X-ray mass measurements. We estimate the effect of background structures based on MMT/Hectospec spectroscopic redshifts and find that these tend to lower M_vir further by ∼7% and increase c_vir by ∼5%.

Using deep 100 and 160 μm observations in GOODS-South from GOODS-Herschel, combined with high-resolution HST/WFC3 near-infrared imaging from CANDELS, we present the first detailed morphological analysis of a complete, far-infrared (FIR) selected sample of 52 ultraluminous infrared galaxies (ULIRGs; L_IR > 10¹² L_☉) at z ∼ 2. We also make use of a comparison sample of galaxies with lower IR luminosities but with the same redshift and H-band magnitude distribution. Our visual classifications of these two samples indicate that the fractions of objects with disk and spheroid morphologies are roughly the same but that there are significantly more mergers, interactions, and irregular galaxies among the ULIRGs (72⁺⁵_{− 7}% versus 32 ± 3%). The combination of disk and irregular/interacting morphologies suggests that early-stage interactions, minor mergers, and disk instabilities could play an important role in ULIRGs at z ∼ 2. We compare these fractions with those of a z ∼ 1 sample selected from GOODS-H and COSMOS across a wide luminosity range and find that the fraction of disks decreases systematically with L_IR while the fraction of mergers and interactions increases, as has been observed locally. At comparable luminosities, the fraction of ULIRGs with various morphological classifications is similar at z ∼ 2 and z ∼ 1, though there are slightly fewer mergers and slightly more disks at higher redshift. We investigate the position of the z ∼ 2 ULIRGs, along with 70 z ∼ 2 LIRGs, on the specific star formation rate versus redshift plane, and find 52 systems to be starbursts (i.e., they lie more than a factor of three above the main-sequence relation). We find that many of these systems are clear interactions and mergers (∼50%) compared to only 24% of systems on the main sequence relation. If irregular disks are included as potential minor mergers, then we find that up to ∼73% of starbursts are involved in a merger or interaction at some level. Although the final coalescence of a major merger may not be required for the high luminosities of ULIRGs at z ∼ 2 as is the case locally, the large fraction (50%–73%) of interactions at all stages and potential minor mergers suggests that these processes contribute significantly to the high star formation rates of ULIRGs at z ∼ 2.

We present a K-band spectroscopic study of the stellar and gas kinematics, mass distribution, and stellar populations of the archetypical starburst galaxy M82. Our results are based on a single spectrum at a position angle of 675 through the K-band nucleus. We used the ¹²CO stellar absorption band head at 2.29 μm (CO_2.29) to measure the rotation curve out to nearly 4 kpc radius on both the eastern and western sides of the galaxy. Our data show that the rotation curve is flat from 1 to 4 kpc. This stands in sharp contrast to some previous studies, which have interpreted H i and CO emission-line position–velocity diagrams as evidence for a declining rotation curve. The kinematics of the Brγ, H₂, and He i emission lines are consistent with, although characterized by slightly higher velocities than, the stellar kinematics. We derived M82's mass distribution from our stellar kinematic measurements and estimate that its total dynamical mass is ∼10¹⁰ M_☉. We measured the equivalent width of CO_2.29 (W_2.29) as a function of distance from the center of the galaxy to investigate the spatial extent of the red supergiant (RSG) population. The variation in W_2.29 with radius clearly shows that RSGs dominate the light inside 500 pc radius. M82's superwind is likely launched from this region, where we estimate that the enclosed mass is ≲2 ×  10⁹ M_☉.

The parsec-scale radio properties of 232 active galactic nuclei, most of which are blazars, detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed contemporaneously by the Very Long Baseline Array (VLBA) at 5 GHz. Data from both the first 11 months (1FGL) and the first 2 years (2FGL) of the Fermi mission were used to investigate these sources' γ-ray properties. We use the ratio of the γ-ray-to-radio luminosity as a measure of γ-ray loudness. We investigate the relationship of several radio properties to γ-ray loudness and to the synchrotron peak frequency. There is a tentative correlation between γ-ray loudness and synchrotron peak frequency for BL Lac objects in both 1FGL and 2FGL, and for flat-spectrum radio quasars (FSRQs) in 2FGL. We find that the apparent opening angle tentatively correlates with γ-ray loudness for FSRQs, but only when we use the 2FGL data. We also find that the total VLBA flux density correlates with the synchrotron peak frequency for BL Lac objects and FSRQs. The core brightness temperature also correlates with synchrotron peak frequency, but only for the BL Lac objects. The low-synchrotron-peaked (LSP) BL Lac object sample shows indications of contamination by FSRQs which happen to have undetectable emission lines. There is evidence that the LSP BL Lac objects are more strongly beamed than the rest of the BL Lac object population.

We study the anisotropy of Ultra-High Energy Cosmic Ray (UHECR) events collected by the Telescope Array (TA) detector in the first 40 months of operation. Following earlier studies, we examine event sets with energy thresholds of 10 EeV, 40 EeV, and 57 EeV. We find that the distributions of the events in right ascension and declination are compatible with an isotropic distribution in all three sets. We then compare with previously reported clustering of the UHECR events at small angular scales. No significant clustering is found in the TA data. We then check the events with E > 57 EeV for correlations with nearby active galactic nuclei. No significant correlation is found. Finally, we examine all three sets for correlations with the large-scale structure (LSS) of the universe. We find that the two higher-energy sets are compatible with both an isotropic distribution and the hypothesis that UHECR sources follow the matter distribution of the universe (the LSS hypothesis), while the event set with E > 10 EeV is compatible with isotropy and is not compatible with the LSS hypothesis at 95% CL unless large deflection angles are also assumed. We show that accounting for UHECR deflections in a realistic model of the Galactic magnetic field can make this set compatible with the LSS hypothesis.

The environment near supermassive black holes (SMBHs) in galactic nuclei contains a large number of stars and compact objects. A fraction of these are likely to be members of binaries. Here we discuss the binary population of stellar black holes and neutron stars near SMBHs and focus on the secular evolution of such binaries, due to the perturbation by the SMBH. Binaries with highly inclined orbits with respect to their orbit around the SMBH are strongly affected by secular Kozai processes, which periodically change their eccentricities and inclinations (Kozai cycles). During periapsis approach, at the highest eccentricities during the Kozai cycles, gravitational wave (GW) emission becomes highly efficient. Some binaries in this environment can inspiral and coalesce at timescales much shorter than a Hubble time and much shorter than similar binaries that do not reside near an SMBH. The close environment of SMBHs could therefore serve as a catalyst for the inspiral and coalescence of binaries and strongly affect their orbital properties. Such compact binaries would be detectable as GW sources by the next generation of GW detectors (e.g., advanced-LIGO). Our analysis shows that ∼0.5% of such nuclear merging binaries will enter the LIGO observational window while on orbits that are still very eccentric (e ≳ 0.5). The efficient GW analysis for such systems would therefore require the use of eccentric templates. We also find that binaries very close to the SMBH could evolve through a complex dynamical (non-secular) evolution, leading to emission of several GW pulses during only a few years (though these are likely to be rare). Finally, we note that the formation of close stellar binaries, X-ray binaries, and their merger products could be induced by similar secular processes, combined with tidal friction rather than GW emission as in the case of compact object binaries.

We present Keck/NIRC2 K_s-band high-contrast coronagraphic imaging of the luminous debris disk around the nearby, young A star HD 32297 resolved at a projected separation of r = 03–25 (≈35–280 AU). The disk is highly warped to the north and exhibits a complex, "wavy" surface brightness (SB) profile interior to r ≈ 110 AU, where the peaks/plateaus in the profiles are shifted between the NE and SW disk lobes. The SW side of the disk is 50%–100% brighter at r = 35–80 AU, and the location of its peak brightness roughly coincides with the disk's millimeter (mm) emission peak. Spectral energy distribution modeling suggests that HD 32297 has at least two dust populations that may originate from two separate belts, likely at different locations, possibly at distances coinciding with the SB peaks. A disk model for a single dust belt including a phase function with two components and a 5–10 AU pericenter offset explains the disk's warped structure and reproduces some of the SB profile's shape (e.g., the overall "wavy" profile, the SB peak/plateau shifts) but more poorly reproduces the disk's brightness asymmetry and the profile at wider separations (r > 110 AU). Although there may be alternate explanations, agreement between the SW disk brightness peak and disk's peak mm emission is consistent with an overdensity of very small, sub-blowout-sized dust and large, 0.1–1 mm sized grains at ≈45 AU tracing the same parent population of planetesimals. New near-IR and submillimeter observations may be able to clarify whether even more complex grain scattering properties or dynamical sculpting by an unseen planet are required to explain HD 32297's disk structure.

The highly eccentric Be binary system δ Sco reached periastron during early 2011 July, when the distance between the primary and secondary was a few times the size of the primary disk in the H band. This opened a window of opportunity to study how the gaseous disks around Be stars respond to gravitational disturbance. We first refine the binary parameters with the best orbital phase coverage data from the Navy Precision Optical Interferometer. Then we present the first imaging results of the disk after the periastron, based on seven nights of five telescope observations with the MIRC combiner at the CHARA array. We found that the disk was inclined 276 ± 60 from the plane of the sky, had a half-light radius of 0.49 mas (2.2 stellar radii), and consistently contributed 71.4% ± 2.7% of the total flux in the H band from night to night, suggesting no ongoing transfer of material into the disk during the periastron. The new estimation of the periastron passage is UT 2011 July 3 07:00 ± 4:30. Re-analysis of archival VLTI-AMBER interferometry data allowed us to determine the rotation direction of the primary disk, constraining it to be inclined either ∼119° or ∼171° relative to the orbital plane of the binary system. We also detect inner disk asymmetries that could be explained by spot-like emission with a few percent of the disk total flux moving in Keplerian orbits, although we lack sufficient angular resolution to be sure of this interpretation and cannot yet rule out spiral density waves or other more complicated geometries.

We report on the observation of the 36 GHz methanol maser line in the star-forming region DR21W to accurately measure the Zeeman effect. The Zeeman signature reported by Fish et al. became suspicious after an instrumental effect was discovered in the early days of the commissioning of the Very Large Array Wide-band Digital Architecture correlator. We conclude that the previously reported magnetic field strength of 58 mG (1.7 Hz mG⁻¹/z) is instrumental in nature and thus incorrect. With the improved performance of the array, we now deduce a 3σ limit of −4.7 to +0.4 mG (1.7 Hz mG⁻¹/z) for the line-of-sight component of the magnetic field strength in DR21W.

A set of hydrodynamical models based on stellar evolutionary progenitors is used to study the nature of SN 2011dh. Our modeling suggests that a large progenitor star—with R ∼ 200 R_☉—is needed to reproduce the early light curve (LC) of SN 2011dh. This is consistent with the suggestion that the yellow super-giant star detected at the location of the supernova (SN) in deep pre-explosion images is the progenitor star. From the main peak of the bolometric LC and expansion velocities, we constrain the mass of the ejecta to be ≈2 M_☉, the explosion energy to be E = (6–10) × 10⁵⁰ erg, and the ⁵⁶Ni mass to be approximately 0.06 M_☉. The progenitor star was composed of a helium core of 3–4 M_☉ and a thin hydrogen-rich envelope of ≈0.1M_☉ with a main-sequence mass estimated to be in the range of 12–15 M_☉. Our models rule out progenitors with helium-core masses larger than 8 M_☉, which correspond to M_ZAMS ≳ 25M_☉. This suggests that a single star evolutionary scenario for SN 2011dh is unlikely.

From a large database of (1) 40,000 SOHO/MDI line-of-sight magnetograms covering the passage of 1300 sunspot active regions across the 30° radius central disk of the Sun, (2) a proxy of each active region's free magnetic energy measured from each of the active region's central-disk-passage magnetograms, and (3) each active region's full-disk-passage history of production of major flares and fast coronal mass ejections (CMEs), we find new statistical evidence that (1) there are aspects of an active region's magnetic field other than the free energy that are strong determinants of the active region's productivity of major flares and fast CMEs in the coming few days; (2) an active region's recent productivity of major flares, in addition to reflecting the amount of free energy in the active region, also reflects these other determinants of coming productivity of major eruptions; and (3) consequently, the knowledge of whether an active region has recently had a major flare, used in combination with the active region's free-energy proxy measured from a magnetogram, can greatly alter the forecast chance that the active region will have a major eruption in the next few days after the time of the magnetogram. The active-region magnetic conditions that, in addition to the free energy, are reflected by recent major flaring are presumably the complexity and evolution of the field.

It is quite common in line formation theory to treat scattering in subordinate lines under the assumption of complete frequency redistribution (CRD). The partial frequency redistribution (PRD) in subordinate lines cannot always be approximated by CRD, especially when the polarization state of the line radiation is taken into account. Here we investigate the PRD effects in subordinate lines including scattering polarization. The line formation is described by a polarized non-LTE line transfer equation based on a two-level atom model. We use the recently derived subordinate line redistribution matrix. We devise polarized approximate lambda iteration methods to solve the concerned transfer problem. The linear polarization profiles of subordinate lines formed in non-magnetic (Rayleigh) scattering atmospheres are discussed. We consider one-dimensional isothermal planar model atmospheres. We show that in the polarized line transfer calculations of subordinate lines, PRD plays as important of a role as it does in the case of resonance lines. We also study the effect of collisions on linear polarization profiles of subordinate lines.

The dissociative recombination (DR) of N₂H⁺ has been reinvestigated at the heavy ion storage ring CRYRING at the Manne Siegbahn Laboratory in Stockholm, Sweden. Thermal rate coefficients for electron temperatures between 10 and 1000 K have been deduced. We show that electron recombination is expected to play an approximately equally important role as CO in the removal of N₂H⁺ in dark interstellar clouds. We note that a deeper knowledge on the influence of the ions' rotational temperature in the DR of N₂H⁺ would be helpful to set further constraints on the relative importance of the different destruction mechanisms for N₂H⁺ in these environments. The branching fractions in the DR of N₂H⁺ have been reinvestigated at ∼0 eV relative kinetic energy, showing a strong dominance of the N₂ + H production channel (93⁺⁴_{− 2}%) with the rest leading to NH + N. These results are in good agreement with flowing afterglow experiments and in disagreement with an earlier measurement at CRYRING.

A unique feature of deflagration-to-detonation (DDT) white dwarf explosion models of supernovae of type Ia is the presence of a strong shock wave propagating through the outer envelope. We consider the early emission expected in such models, which is produced by the expanding shock-heated outer part of the ejecta and precedes the emission driven by radioactive decay. We expand on earlier analyses by considering the modification of the pre-detonation density profile by the weak shocks generated during the deflagration phase, the time evolution of the opacity, and the deviation of the post-shock equation of state from that obtained for radiation pressure domination. A simple analytic model is presented and shown to provide an acceptable approximation to the results of one-dimensional numerical DDT simulations. Our analysis predicts a ∼10³ s long UV/optical flash with a luminosity of ∼1 to ∼3 × 10³⁹ erg s⁻¹. Lower luminosity corresponds to faster (turbulent) deflagration velocity. The luminosity of the UV flash is predicted to be strongly suppressed at t > t_drop ∼ 1 hr due to the deviation from pure radiation domination.

We explore possible systematic errors in the mass measurements of stellar mass black holes (BHs). We find that significant errors can arise from the assumption of zero or constant emission from the accretion flow, which is commonly used when determining orbital inclination by modeling ellipsoidal variations. For A0620−00, the system with the best available data, we show that typical data sets and analysis procedures can lead to systematic underestimates of the inclination by 10° or more. A careful examination of the available data for the 15 other X-ray transients with low-mass donors suggests that this effect may significantly reduce the BH mass estimates in several other cases, most notably that of GRO J0422+32. Assuming that GRO J0422+32 behaves similarly to A0620−00, the reduction in the mass of GRO J0422+32 fills the mass gap between the low end of the distribution and the maximum theoretical neutron star mass, as has been identified in previous studies. Otherwise, we find that the mass distribution retains other previously identified characteristics, namely a peak around 8 M_☉, a paucity of sources with masses below 5 M_☉, and a sharp drop-off above 10 M_☉.

We investigate the dynamical evolution of the Orion Nebula Cluster (ONC) by means of direct N-body integrations. A large fraction of residual gas was probably expelled when the ONC formed, so we assume that the ONC was much more compact when it formed compared with its current size, in agreement with the embedded cluster radius–mass relation from Marks & Kroupa. Hence, we assume that few-body relaxation played an important role during the initial phase of evolution of the ONC. In particular, three-body interactions among OB stars likely led to their ejection from the cluster and, at the same time, to the formation of a massive object via "runaway" physical stellar collisions. The resulting depletion of the high-mass end of the stellar mass function in the cluster is one of the important points where our models fit the observational data. We speculate that the runaway-mass star may have collapsed directly into a massive black hole (M_• ≳ 100 M_☉). Such a dark object could explain the large velocity dispersion of the four Trapezium stars observed in the ONC core. We further show that the putative massive black hole is likely to be a member of a binary system with ≈70% probability. In such a case, it could be detected either due to short periods of enhanced accretion of stellar winds from the secondary star during pericentre passages, or through a measurement of the motion of the secondary whose velocity would exceed 10 km s⁻¹ along the whole orbit.

We have searched for prompt radio emission from nine gamma-ray bursts (GRBs) with a 12 m telescope at 1.4 GHz, with a time resolution of 64 μs to 1 s. We detected single dispersed radio pulses with significances >6σ in the few minutes following two GRBs. The dispersion measures of both pulses are well in excess of the expected Galactic values, and the implied rate is incompatible with known sources of single dispersed pulses. The arrival times of both pulses also coincide with breaks in the GRB X-ray light curves. A null trial and statistical arguments rule out random fluctuations as the origin of these pulses with >95% and ∼97% confidence, respectively, although a simple population argument supports a GRB origin with confidence of only 2%. We caution that we cannot rule out radio frequency interference (RFI) as the origin of these pulses. If the single pulses are not related to the GRBs, we set an upper limit on the flux density of radio pulses emitted between 200 and 1800 s after a GRB of 1.27w^−1/2 Jy, where 6.4 × 10⁻⁵ s < w < 32 × 10⁻³ s is the pulse width. We set a limit of less than 760 Jy for long timescale (>1 s) variations. These limits are some of the most constraining at high time resolution and GHz frequencies in the early stages of the GRB phenomenon.

We report on the analysis of two XMM-Newton observations of the recently discovered soft gamma repeater Swift J1834.9−0846, taken in 2005 September and one month after the source went into outburst on 2011 August 7. We performed timing and spectral analyses on the point source as well as on the extended emission. We find that the source period is consistent with an extrapolation of the Chandra ephemeris reported earlier and the spectral properties remained constant. The source luminosity decreased to a level of 1.6 × 10³⁴ erg s⁻¹ following a decay trend of ∝t^−0.5. Our spatial analysis of the source environment revealed the presence of two extended emission regions around the source. The first (region A) is a symmetric ring around the point source, starting at 25'' and extending to ∼50''. We argue that region A is a dust scattering halo. The second (region B) has an asymmetrical shape extending between 50'' and 150'', and is detected both in the pre- and post-outburst data. We argue that this region is a possible magnetar wind nebula (MWN). The X-ray efficiency of the MWN with respect to the rotation energy loss is substantially higher than those of rotation-powered pulsars: $\eta _{\rm X}\equiv L_{\rm MWN,0.5\hbox{\scriptsize --}8 \,keV}/\dot{E}_{\rm rot}\approx 0.7$. The higher efficiency points to a different energy source for the MWN of Swift J1834.9−0846, most likely bursting activity of the magnetar, powered by its high magnetic field, B = 1.4 × 10¹⁴ G.

We examined 134 Chandra observations of the population of X-ray sources associated with globular clusters (GCs) in the central region of M31. These are expected to be X-ray binary systems (XBs), consisting of a neutron star or black hole accreting material from a close companion. We created long-term light curves for these sources, correcting for background, interstellar absorption, and instrumental effects. We tested for variability by examining the goodness of fit for the best-fit constant intensity. We also created structure functions (SFs) for every object in our sample, the first time this technique has been applied to XBs. We found significant variability in 28 out of 34 GCs and GC candidates; the other 6 sources had 0.3–10 keV luminosities fainter than ∼2 × 10³⁶ erg s⁻¹, limiting our ability to detect similar variability. The SFs of XBs with 0.3–10 keV luminosities ∼2–50 × 10³⁶ erg s⁻¹ generally showed considerably more variability than the published ensemble SF of active galactic nuclei (AGNs). Our brightest XBs were mostly consistent with the AGN SF; however, their 2–10 keV fluxes could be matched by <1 AGN per square degree. These encouraging results suggest that examining the long-term light curves of other X-ray sources in the field may provide an important distinction between X-ray binaries and background galaxies, as the X-ray emission spectra from these two classes of X-ray sources are similar. Additionally, we identify 3 new black hole candidates (BHCs) using additional XMM-Newton data, bringing the total number of M31 GC BHCs to 9, with 8 covered in this survey.

We compare and analyze the Spitzer mid-infrared spectrum of three fullerene-rich planetary nebulae in the Milky Way and the Magellanic Clouds: Tc1, SMP SMC 16, and SMP LMC 56. The three planetary nebulae share many spectroscopic similarities. The strongest circumstellar emission bands correspond to the infrared active vibrational modes of the fullerene species C₆₀ and little or no emission is present from polycyclic aromatic hydrocarbons. The strengths of the fullerene bands in the three planetary nebulae are very similar, while the ratios of the [Ne iii]15.5 μm/[Ne ii]12.8 μm fine structure lines, an indicator of the strength of the radiation field, are markedly different. This raises questions about their excitation mechanism and we compare the fullerene emission to fluorescent and thermal models. In addition, the spectra show other interesting and common features, most notably in the 6–9 μm region, where a broad plateau with substructure dominates the emission. These features have previously been associated with mixtures of aromatic/aliphatic hydrocarbon solids. We hypothesize on the origin of this band, which is likely related to the fullerene formation mechanism, and compare it with modeled hydrogenated amorphous carbon that present emission in this region.

We examine the agreement between the observed and theoretical low-mass (<0.8 M_☉) stellar main-sequence mass–radius relationship by comparing detached eclipsing binary (DEB) data with a new, large grid of stellar evolution models. The new grid allows for a realistic variation in the age and metallicity of the DEB population, characteristic of the local galactic neighborhood. Overall, our models do a reasonable job of reproducing the observational data. A large majority of the models match the observed stellar radii to within 4%, with a mean absolute error of 2.3%. These results represent a factor of two improvement compared to previous examinations of the low-mass mass–radius relationship. The improved agreement between models and observations brings the radius deviations within the limits imposed by potential starspot-related uncertainties for 92% of the stars in our DEB sample.

We present near-infrared (NIR; J and K_s) survey of the Great Observatories Origins Deep Survey-North (GOODS-N) field. The publicly available imaging data were obtained using the MOIRCS instrument on the 8.2 m Subaru and the WIRCam instrument on the 3.6 m Canada–France–Hawaii Telescope (CFHT). These observations fulfill a serious wavelength gap in the GOODS-N data, i.e., lack of deep NIR observations. We combine the Subaru/MOIRCS and CFHT/WIRCam archival data to generate deep J- and K_s-band images, covering the full GOODS-N field (∼169 arcmin²) to an AB magnitude limit of ∼25 mag (3σ). We applied z₈₅₀-band dropout color selection criteria, using the NIR data generated here. We have identified two possible Lyman break galaxy (LBG) candidates at z ≳ 6.5 with J ≲ 24.5. The first candidate is a likely LBG at z ≃ 6.5 based on a weak spectral feature tentatively identified as Lyα line in the deep Keck/DEIMOS spectrum, while the second candidate is a possible LBG at z ≃ 7 based on its photometric redshift. These z₈₅₀-dropout objects, if confirmed, are among the brightest such candidates found so far. At z ≳ 6.5, their star formation rate is estimated as 100–200 M_☉ yr⁻¹. If they continue to form stars at this rate, they assemble a stellar mass of ∼5 × 10¹⁰ M_☉ after about 400 million years, becoming the progenitors of massive galaxies observed at z ≃ 5. We study the implication of the z₈₅₀-band dropout candidates discovered here, in constraining the bright end of the luminosity function and understanding the nature of high-redshift galaxies.

We present light-cone-integrated simulations of the cosmic microwave background (CMB) polarization signal induced by a single scattering in the direction of clusters of galaxies and filaments. We characterize the statistical properties of the induced polarization signals from the presence of the CMB quadrupole component (pqiCMB) and as the result of the transverse motion of ionized gas clouds with respect to the CMB rest frame (pβ²_tSZ). From adiabatic N-body/hydrodynamic simulations, we generated 28 random sky patches integrated along the light cone, each with about 0.86 deg² and angular resolution of 6''. Our simulation method involves a box-stacking scheme that allows to reconstruct the CMB quadrupole component and the gas physical properties along the line of sight. We find that the linear polarization degree in the logarithmic scale of both effects follows approximately a Gaussian distribution and the mean total signal is about 10⁻⁸ and 10⁻¹⁰ for the pqiCMB and pβ²_tSZ effects, respectively. The polarization angle is consistent with a flat distribution in both cases. From the mean distributions of the polarization degree with redshift, the highest peak is found at z ≃ 1 for the induced CMB quadrupole and at z ≃ 0.5 for the kinematic component. Our results suggest that most of the contribution for the total polarization signal arises from z ≲ 4 for the pqiCMB and z ≲ 3 for pβ²_tSZ. The spectral dependency of both integrated signals is strong, increasing with the frequency, especially in the case of the pβ²_tSZ signal, which increases by a factor of 100 from 30 GHz to 675 GHz. The maxima values found at the highest frequency are about 3 μK and 13 μK for the pqiCMB and pβ²_tSZ, respectively. The angular power spectra of these effects peak at large multipoles ℓ > 10⁴, being of the order of 10⁻⁵ μK² for pqiCMB polarization and 10⁻⁷ μK² for the pβ²_tSZ effect. Therefore, these effects will not be a relevant source of contamination for measurements of the primary polarization modes, and at larger multipoles of roughly ℓ > 40, 000, pqiCMB may be the dominant component over the primary and lensing signals.

We analyze the generation of polarization cross-talk in Stokes polarimeters by atmospheric seeing, and its effects on the noise statistics of spectropolarimetric measurements for both single-beam and dual-beam instruments. We investigate the time evolution of seeing-induced correlations between different states of one modulation cycle and compare the response to these correlations of two popular polarization modulation schemes in a dual-beam system. Extension of the formalism to encompass an arbitrary number of modulation cycles enables us to compare our results with earlier work. Even though we discuss examples pertinent to solar physics, the general treatment of the subject and its fundamental results might be useful to a wider community.

We present comprehensive experimental line lists of methane (CH₄) at high temperatures obtained by recording Fourier transform infrared emission spectra. Calibrated line lists are presented for the temperatures 300–1400°C at twelve 100°C intervals spanning the 960–5000 cm⁻¹ (2.0–10.4 μm) region of the infrared. This range encompasses the dyad, pentad, and octad regions, i.e., all fundamental vibrational modes along with a number of combination, overtone and hot bands. Using our CH₄ spectra, we have estimated empirical lower state energies (E_low in cm⁻¹) and our values have been incorporated into the line lists along with line positions ($\tilde{\nu }$ in cm⁻¹) and calibrated line intensities (S' in cm molecule⁻¹). We expect our hot CH₄ line lists to find direct application in the modeling of planetary atmospheres and brown dwarfs.

We present models of ohmic heating in the interiors of hot Jupiters in which we decouple the interior and the wind zone by replacing the wind zone with a boundary temperature T_iso and magnetic field B_ϕ0. Ohmic heating influences the contraction of gas giants in two ways: by direct heating within the convection zone and by heating outside the convection zone, which increases the effective insulation of the interior. We calculate these effects and show that internal ohmic heating is only able to slow the contraction rate of a cooling gas giant once the planet reaches a critical value of internal entropy. We determine the age of the gas giant when ohmic heating becomes important as a function of mass, T_iso, and induced B_ϕ0. With this survey of parameter space complete, we then adopt the wind zone scalings of Menou and calculate the expected evolution of gas giants with different levels of irradiation. We find that, with this prescription of magnetic drag, it is difficult to inflate massive planets or those with strong irradiation using ohmic heating, meaning that we are unable to account for many of the observed hot Jupiter radii. This is in contrast to previous evolutionary models that assumed that a constant fraction of the irradiation is transformed into ohmic power.

We combine an N-body simulation algorithm with a subgrid treatment of galaxy formation, mergers, and tidal destruction, and an observed conditional luminosity function Φ(L|M), to study the origin and evolution of galactic and extragalactic light inside a cosmological volume of size (100 Mpc)³, in a concordance ΛCDM model. This algorithm simulates the growth of large-scale structures and the formation of clusters, the evolution of the galaxy population in clusters, the destruction of galaxies by mergers and tides, and the evolution of the intracluster light (ICL). We find that destruction of galaxies by mergers dominates over destruction by tides by about an order of magnitude at all redshifts. However, tidal destruction is sufficient to produce ICL fractions f_ICL that are sufficiently high to match observations. Our simulation produces 18 massive clusters (M_cl > 10¹⁴ M_☉) with values of f_ICL ranging from 1% to 58% at z = 0. There is a weak trend of f_ICL to increase with cluster mass. The bulk of the ICL (∼60%) is provided by intermediate galaxies of total masses 10¹¹–10¹² M_☉ and stellar masses 6 × 10⁸ M_☉ to 3 × 10¹⁰ M_☉ that were tidally destroyed by even more massive galaxies. The contribution of low-mass galaxies to the ICL is small and the contribution of dwarf galaxies is negligible, even though, by numbers, most galaxies that are tidally destroyed are dwarfs. Tracking clusters back in time, we find that their values of f_ICL tend to increase over time, but can experience sudden changes that are sometimes non-monotonic. These changes occur during major mergers involving clusters of comparable masses but very different intracluster luminosities. Most of the tidal destruction events take place in the central regions of clusters. As a result, the ICL is more centrally concentrated than the galactic light. Our results support tidal destruction of intermediate-mass galaxies as a plausible scenario for the origin of the ICL.

We study the temporal evolution of umbral dots (UDs) using measurements from the CRISP imaging spectropolarimeter at the Swedish 1 m Solar Telescope. Scans of the magnetically sensitive 630 nm iron lines were performed under stable atmospheric conditions for 71 minutes with a cadence of 63 s. These observations allow us to investigate the magnetic field and velocity in and around UDs at a resolution approaching 013. From the analysis of 339 UDs, we draw the following conclusions: (1) UDs show clear hints of upflows, as predicted by magnetohydrodynamic simulations. By contrast, we could not find systematic downflow signals. Only in very deep layers, we detect localized downflows around UDs, but they do not persist in time. (2) We confirm that UDs exhibit weaker and more inclined fields than their surroundings, as reported previously. However, UDs that have strong fields above 2000 G or are in the decay phase show enhanced and more vertical fields. (3) There are enhanced fields at the migration front of UDs detached from penumbral grains, as if their motion were impeded by the ambient field. (4) Long-lived UDs travel longer distances with slower proper motions. Our results appear to confirm some aspects of recent numerical simulations of magnetoconvection in the umbra (e.g., the existence of upflows in UDs), but not others (e.g., the systematic weakening of the magnetic field at the position of UDs).

The outward migration of a pair of resonant-orbit planets, driven by tidal interactions with a gas-dominated disk, is studied in the context of evolved solar nebula models. The planets' masses, M₁ and M₂, correspond to those of Jupiter and Saturn. Hydrodynamical calculations in two and three dimensions are used to quantify the migration rates and analyze the conditions under which the outward migration mechanism may operate. The planets are taken to be fully formed after 10⁶ and before 3 × 10⁶ years. The orbital evolution of the planets in an evolving disk is then calculated until the disk's gas is completely dissipated. Orbital locking in the 3:2 mean motion resonance may lead to outward migration under appropriate conditions of disk viscosity and temperature. However, resonance locking does not necessarily result in outward migration. This is the case, for example, if convergent migration leads to locking in the 2:1 mean motion resonance, as post-formation disk conditions seem to suggest. Accretion of gas on the planets may deactivate the outward migration mechanism by raising the mass ratio M₂/M₁ and/or by reducing the accretion rate toward the star, and hence depleting the inner disk. For migrating planets locked in the 3:2 mean motion resonance, there are stalling radii that depend on disk viscosity and on stellar irradiation, when it determines the disk's thermal balance. Planets locked in the 3:2 orbital resonance that start moving outward from within 1–2 AU may reach beyond ≈5 AU only under favorable conditions. However, within the explored space of disk parameters, only a small fraction—less than a few percent—of the models predict that the interior planet reaches beyond ≈4 AU.

We present a sample of 120 dust-reddened quasars identified by matching radio sources detected at 1.4 GHz in the Faint Images of the Radio Sky at Twenty Centimeters survey with the near-infrared Two Micron All Sky Survey catalog and color-selecting red sources. Optical and/or near-infrared spectroscopy provide broad wavelength sampling of their spectral energy distributions that we use to determine their reddening, characterized by E(B − V). We demonstrate that the reddening in these quasars is best described by Small-Magellanic-Cloud-like dust. This sample spans a wide range in redshift and reddening (0.1 ≲ z ≲ 3, 0.1 ≲ E(B − V) ≲ 1.5), which we use to investigate the possible correlation of luminosity with reddening. At every redshift, dust-reddened quasars are intrinsically the most luminous quasars. We interpret this result in the context of merger-driven quasar/galaxy co-evolution where these reddened quasars are revealing an emergent phase during which the heavily obscured quasar is shedding its cocoon of dust prior to becoming a "normal" blue quasar. When correcting for extinction, we find that, depending on how the parent population is defined, these red quasars make up ≲ 15%–20% of the luminous quasar population. We estimate, based on the fraction of objects in this phase, that its duration is 15%–20% as long as the unobscured, blue quasar phase.

The correlation between infrared-to-ultraviolet luminosity ratio and ultraviolet color (or ultraviolet spectral slope), i.e., the IRX–UV (or IRX–β) relation, found in studies of starburst galaxies is a prevalent recipe for correcting extragalactic dust attenuation. Considerable dispersion in this relation discovered for normal galaxies, however, complicates its usability. In order to investigate the cause of the dispersion and to have a better understanding of the nature of the IRX–UV relation, in this paper, we select five nearby spiral galaxies, and perform spatially resolved studies on each of the galaxies, with a combination of ultraviolet and infrared imaging data. We measure all positions within each galaxy and divide the extracted regions into young and evolved stellar populations. By means of this approach, we attempt to discover separate effects of dust attenuation and stellar population age on the IRX–UV relation for individual galaxies. In this work, in addition to dust attenuation, stellar population age is interpreted to be another parameter in the IRX–UV function, and the diversity of star formation histories is suggested to disperse the age effects. At the same time, strong evidence shows the need for more parameters in the interpretation of observational data, such as variations in attenuation/extinction law. Fractional contributions of different components to the integrated luminosities of the galaxies suggest that the integrated measurements of these galaxies, which comprise different populations, would weaken the effect of the age parameter on IRX–UV diagrams. The dependence of the IRX–UV relation on luminosity and radial distance in galaxies presents weak trends, which offers an implication of selective effects. The two-dimensional maps of the UV color and the infrared-to-ultraviolet ratio are displayed and show a disparity in the spatial distributions between the two galaxy parameters, which offers a spatial interpretation of the scatter in the IRX–UV relation.

We have undertaken a new ground-based monitoring campaign on the broad-line radio galaxy 3C 390.3 to improve the measurement of the size of the broad emission-line region and to estimate the black hole mass. Optical spectra and g-band images were observed in late 2005 for three months using the 2.4 m telescope at MDM Observatory. Integrated emission-line flux variations were measured for the hydrogen Balmer lines Hα, Hβ, Hγ, and for the helium line He iiλ4686, as well as g-band fluxes and the optical active galactic nucleus (AGN) continuum at λ = 5100 Å. The g-band fluxes and the optical AGN continuum vary simultaneously within the uncertainties, τ_cent = (0.2 ± 1.1) days. We find that the emission-line variations are delayed with respect to the variable g-band continuum by τ(Hα) = 56.3^+2.4_{− 6.6} days, τ(Hβ) = 44.3^+3.0_{− 3.3} days, τ(Hγ) = 58.1^+4.3_{− 6.1} days, and τ(He ii 4686) = 22.3^+6.5_{− 3.8} days. The blue and red peaks in the double-peaked line profiles, as well as the blue and red outer profile wings, vary simultaneously within ±3 days. This provides strong support for gravitationally bound orbital motion of the dominant part of the line-emitting gas. Combining the time delay of the strong Balmer emission lines of Hα and Hβ and the separation of the blue and red peaks in the broad double-peaked profiles in their rms spectra, we determine M^vir_bh = 1.77^+0.29_{− 0.31} × 10⁸ M_☉ and using σ_line of the rms spectra M^vir_bh = 2.60^+0.23_{− 0.31} × 10⁸ M_☉ for the central black hole of 3C 390.3, respectively. Using the inclination angle of the line-emitting region which is measured from superluminal motion detected in the radio range, accretion disk models to fit the optical double-peaked emission-line profiles, and X-ray observations, the mass of the black hole amounts to M_bh = 0.86^+0.19_{− 0.18} × 10⁹ M_☉ (peak separation) and M_bh = 1.26^+0.21_{− 0.16} × 10⁹ M_☉ (σ_line), respectively. This result is consistent with the black hole masses indicated by simple accretion disk models to describe the observed double-peaked profiles, derived from the stellar dynamics of 3C 390.3, and with the AGN radius–luminosity relation. Thus, 3C 390.3 as a radio-loud AGN with a low Eddington ratio, L_edd/L_bol = 0.02, follows the same AGN radius–luminosity relation as radio-quiet AGNs.

In this contribution, we present the first census of oxygen in star-forming galaxies in the local universe. We examine three samples of galaxies with metallicities and star formation rates (SFRs) at z = 0.07, 0.8, and 2.26, including the Sloan Digital Sky Survey (SDSS) and DEEP2 survey. We infer the total mass of oxygen produced and mass of oxygen found in the gas-phase from our local SDSS sample. The star formation history is determined by requiring that galaxies evolve along the relation between stellar mass and SFR observed in our three samples. We show that the observed relation between stellar mass and SFR for our three samples is consistent with other samples in the literature. The mass–metallicity relation is well established for our three samples, and from this we empirically determine the chemical evolution of star-forming galaxies. Thus, we are able to simultaneously constrain the SFRs and metallicities of galaxies over cosmic time, allowing us to estimate the mass of oxygen locked up in stars. Combining this work with independent measurements reported in the literature, we conclude that the loss of oxygen from the interstellar medium of local star-forming galaxies is likely to be a ubiquitous process with the oxygen mass loss scaling (almost) linearly with stellar mass. We estimate the total baryonic mass loss and argue that only a small fraction of the baryons inferred from cosmological observations accrete onto galaxies.

We investigate the distribution of neutron star masses in different populations of binaries, employing Bayesian statistical techniques. In particular, we explore the differences in neutron star masses between sources that have experienced distinct evolutionary paths and accretion episodes. We find that the distribution of neutron star masses in non-recycled eclipsing high-mass binaries as well as of slow pulsars, which are all believed to be near their birth masses, has a mean of 1.28 M_☉ and a dispersion of 0.24 M_☉. These values are consistent with expectations for neutron star formation in core-collapse supernovae. On the other hand, double neutron stars, which are also believed to be near their birth masses, have a much narrower mass distribution, peaking at 1.33 M_☉, but with a dispersion of only 0.05 M_☉. Such a small dispersion cannot easily be understood and perhaps points to a particular and rare formation channel. The mass distribution of neutron stars that have been recycled has a mean of 1.48 M_☉ and a dispersion of 0.2 M_☉, consistent with the expectation that they have experienced extended mass accretion episodes. The fact that only a very small fraction of recycled neutron stars in the inferred distribution have masses that exceed ∼2 M_☉ suggests that only a few of these neutron stars cross the mass threshold to form low-mass black holes.

Most gamma-ray bursts (GRBs) have erratic light curves, which demand that the GRB central engine launches an episodic outflow. Recent Fermi observations of some GRBs indicate a lack of the thermal photosphere component as predicted by the baryonic fireball model, which suggests a magnetic origin of GRBs. Given that powerful episodic jets have been observed along with continuous jets in other astrophysical black hole systems, here we propose an intrinsically episodic, magnetically dominated jet model for the GRB central engine. Accumulation and eruption of free magnetic energy in the corona of a differentially rotating, turbulent accretion flow around a hyperaccreting black hole lead to ejections of episodic, magnetically dominated plasma blobs. These blobs are accelerated magnetically, collide with each other at large radii, trigger rapid magnetic reconnection and turbulence, efficient particle acceleration, and radiation, and power the observed episodic prompt gamma-ray emission from GRBs.

We report low-resolution near-infrared spectroscopic observations of the eruptive star FU Orionis using the Integral Field Spectrograph (IFS) Project 1640 installed at the Palomar Hale telescope. This work focuses on elucidating the nature of the faint source, located 05 south of FU Ori, and identified in 2003 as FU Ori S. We first use our observations in conjunction with published data to demonstrate that the two stars are indeed physically associated and form a true binary pair. We then proceed to extract J- and H-band spectro-photometry using the damped LOCI algorithm, a reduction method tailored for high contrast science with IFS. This is the first communication reporting the high accuracy of this technique, pioneered by the Project 1640 team, on a faint astronomical source. We use our low-resolution near-infrared spectrum in conjunction with 10.2 μm interferometric data to constrain the infrared excess of FU Ori S. We then focus on estimating the bulk physical properties of FU Ori S. Our models lead to estimates of an object heavily reddened, A_V = 8–12, with an effective temperature of ∼4000–6500 K. Finally, we put these results in the context of the FU Ori N-S system and argue that our analysis provides evidence that FU Ori S might be the more massive component of this binary system.

We report on high-sensitivity and high angular resolution archival Submillimeter Array observations of the large (∼15,000 AU) putative circumstellar disk associated with the O-type protostar NGC 7538 S. Observations of the continuum resolve this putative circumstellar disk into five compact sources, with sizes ∼3000 AU and masses ∼10 M_☉. This confirms the results of recent millimeter observations made with CARMA/BIMA toward this object. However, we find that most of these compact sources eject collimated bipolar outflows, revealed by our silicon monoxide (SiO J = 5–4) observations, and confirm that these sources have a (proto)stellar nature. All outflows are perpendicular to the large and rotating dusty structure. We propose therefore that, rather than being a single massive circumstellar disk, NGC 7538 S could instead be a large and massive contracting or rotating filament that is fragmenting at scales of 0.1–0.01 pc to form several B-type stars, via the standard process involving outflows and disks. As in recent high spatial resolution studies of dusty filaments, our observations also suggest that thermal pressure does not seem to be sufficient to support the filament, so that either additional support needs to be invoked or else the filament must be in the process of collapsing. A smoothed particle hydrodynamics numerical simulation of the formation of a molecular cloud by converging warm neutral medium flows produces contracting filaments whose dimensions and spacings between the stars forming within them, as well as their column densities, strongly resemble those observed in the filament reported here.

Dust and gas energetics are incorporated into a cluster-scale simulation of star formation in order to study the effect of heating and cooling on the star formation process. We build on our previous work by calculating separately the dust and gas temperatures. The dust temperature is set by radiative equilibrium between heating by embedded stars and radiation from dust. The gas temperature is determined using an energy-rate balance algorithm which includes molecular cooling, dust–gas collisional energy transfer, and cosmic-ray ionization. The fragmentation proceeds roughly similarly to simulations in which the gas temperature is set to the dust temperature, but there are differences. The structure of regions around sink particles has properties similar to those of Class 0 objects, but the infall speeds and mass accretion rates are, on average, higher than those seen for regions forming only low-mass stars. The gas and dust temperature have complex distributions not well modeled by approximations that ignore the detailed thermal physics. There is no simple relationship between density and kinetic temperature. In particular, high-density regions have a large range of temperatures, determined by their location relative to heating sources. The total luminosity underestimates the star formation rate at these early stages, before ionizing sources are included, by an order of magnitude. As predicted in our previous work, a larger number of intermediate-mass objects form when improved thermal physics is included, but the resulting initial mass function (IMF) still has too few low-mass stars. However, if we consider recent evidence on core-to-star efficiencies, the match to the IMF is improved.

We study the evolution of galactic bars and the link with disk and spheroid formation in a sample of zoom-in cosmological simulations. Our simulation sample focuses on galaxies with present-day stellar masses in the 10¹⁰–10¹¹ M_☉ range, in field and loose group environments, with a broad variety of mass growth histories. In our models, bars are almost absent from the progenitors of present-day spirals at z > 1.5, and they remain rare and generally too weak to be observable down to z ≈ 1. After this characteristic epoch, the fractions of observable and strong bars rise rapidly, bars being present in 80% of spiral galaxies and easily observable in two thirds of these at z ⩽ 0.5. This is quantitatively consistent with the redshift evolution of the observed bar fraction, although the latter is presently known up to z ≈ 0.8 because of band-shifting and resolution effects. Our models hence predict that the decrease in the bar fraction with increasing redshift should continue with a fraction of observable bars not larger than 10%–15% in disk galaxies at z > 1. Our models also predict later bar formation in lower-mass galaxies, in agreement with existing data. We find that the characteristic epoch of bar formation, namely redshift z ≈ 0.8–1 in the studied mass range, corresponds to the epoch at which today's spirals acquire their disk-dominated morphology. At higher redshift, disks tend to be rapidly destroyed by mergers and gravitational instabilities and rarely develop significant bars. We hence suggest that the bar formation epoch corresponds to the transition between an early "violent" phase of spiral galaxy formation at z ⩾ 1 and a late "secular" phase at z ⩽ 0.8. In the secular phase, the presence of bars substantially contributes to the growth of the (pseudo-)bulge, but the bulge mass budget remains statistically dominated by the contribution of mergers, interactions, and disk instabilities at high redshift. Early bars at z > 1 are often short-lived, while most of the bars formed at z ⩽ 1 persist down to z = 0, late cosmological gas infall being necessary to maintain some of them.

We study the origin of the extragalactic diffuse gamma-ray background using the data from the Fermi telescope. To estimate the background level, we count photons at high Galactic latitudes |b| > 60°. Subtracting photons associated with known sources and the residual cosmic-ray and Galactic diffuse backgrounds, we estimate the extragalactic gamma-ray background (EGB) flux. We find that the spectrum of EGB in the very high energy band above 30 GeV follows the stacked spectrum of BL Lac objects. Large Area Telescope data reveal the positive (1 + z)^k, 1 < k < 4 cosmological evolution of the BL Lac source population consistent with that of their parent population, Fanaroff–Riley type I radio galaxies. We show that EGB at E > 30 GeV could be completely explained by emission from unresolved BL Lac objects if k ≃ 3.

We describe a method for estimating physical conditions in the broad-line region (BLR) for a significant subsample of Seyfert 1 nuclei and quasars. Several diagnostic ratios based on intermediate (Al iii λ1860, Si iii] λ1892) and high (C iv λ1549, Si iv λ1397) ionization lines in the UV spectra of quasars are used to constrain density, ionization, and metallicity of the emitting gas. We apply the method to two extreme Population A quasars—the prototypical NLSy1 I Zw 1 and higher z source SDSS J120144.36+011611.6. Under assumptions of spherical symmetry and pure photoionization we infer BLR physical conditions: low ionization (ionization parameter <10⁻²), high density (10¹²–10¹³ cm⁻³), and significant metal enrichment. Ionization parameter and density can be derived independently for each source with an uncertainty that is less than ±0.3 dex. We use the product of density and ionization parameter to estimate the BLR radius and derive an estimation of the virial black hole mass (M_BH). Estimates of M_BH based on the "photoionization" analysis described in this paper are probably more accurate than those derived from the mass–luminosity correlations widely employed to compute black hole masses for high-redshift quasars.

We present the first detailed study of the stellar populations of star-forming galaxies at z ∼ 1.5, which are selected by their [O ii] emission line, detected in narrowband surveys. We identified ∼1300 [O ii] emitters at z = 1.47 and z = 1.62 in the Subaru Deep Field with rest-frame equivalent widths (EWs) above 13 Å. Optical and near-infrared spectroscopic observations for ≈10% of our samples show that our separation of [O ii] from [O iii] emission-line galaxies in two-color space is 99% successful. We analyze the multi-wavelength properties of a subset of ∼1200 galaxies with the best photometry. They have average rest-frame EW of 45 Å, stellar mass of 3 × 10⁹M_☉, and stellar age of 100 Myr. In addition, our spectral energy distribution (SED) fitting and broadband colors indicate that [O ii] emitters span the full range of galaxy populations at z ∼ 1.5. We also find that 80% of [O ii] emitters are also photometrically classified as "BX/BM" (UV) galaxies and/or the star-forming "BzK" (near-IR) galaxies. Our [O ii] emission line survey produces a far more complete and somewhat deeper sample of z ∼ 1.5 galaxies than either the BX/BM or sBzK selection alone. We constructed average SEDs and find that higher [O ii] EW galaxies have somewhat bluer continua. SED model-fitting shows that they have on average half the stellar mass of galaxies with lower [O ii] EW. The observed [O ii] luminosity is well correlated with the far-UV continuum with a logarithmic slope of 0.89 ± 0.22. The scatter of the [O ii] luminosity against the far-UV continuum suggests that [O ii] can be used as a star formation rate indicator with a reliability of 0.23 dex.

We combine new deep and wide field of view Hα imaging of a sample of eight nearby (d ≈ 17 Mpc) spiral galaxies with new and archival H i and CO imaging to study the star formation and the star formation regulation in the outer disk. We find that, in agreement with previous studies, star formation in the outer disk has low covering fractions, and star formation is typically organized into spiral arms. The star formation in the outer disk is at extremely low levels, with typical star formation rate surface densities of ∼10⁻⁵ to 10⁻⁶ M_☉ yr⁻¹ kpc⁻². We find that the ratio of the radial extent of detected H ii regions to the radius of the H i disk is typically ≳85%. This implies that in order to further our understanding of the implications of extended star formation, we must further our understanding of the formation of extended H i disks. We measure the gravitational stability of the gas disk, and find that the outer gaseous disk is typically a factor of ∼2 times more stable than the inner star-forming disk. We measure the surface density of outer disk H i arms, and find that the disk is closer to gravitational instability along these arms. Therefore, it seems that spiral arms are a necessary, but not sufficient, requirement for star formation in the outer disk. We use an estimation of the flaring of the outer gas disk to illustrate the effect of flaring on the Schmidt power-law index; we find that including flaring increases the agreement between the power-law indices of the inner and outer disks.

We investigate the launching of jets and outflows from magnetically diffusive accretion disks. Using the PLUTO code, we solve the time-dependent resistive magnetohydrodynamic equations taking into account the disk and jet evolution simultaneously. The main question we address is which kind of disks launch jets and which kind of disks do not? In particular, we study how the magnitude and distribution of the (turbulent) magnetic diffusivity affect mass loading and jet acceleration. We apply a turbulent magnetic diffusivity based on α-prescription, but also investigate examples where the scale height of diffusivity is larger than that of the disk gas pressure. We further investigate how the ejection efficiency is governed by the magnetic field strength. Our simulations last for up to 5000 dynamical timescales corresponding to 900 orbital periods of the inner disk. As a general result, we observe a continuous and robust outflow launched from the inner part of the disk, expanding into a collimated jet of superfast-magnetosonic speed. For long timescales, the disk's internal dynamics change, as due to outflow ejection and disk accretion the disk mass decreases. For magnetocentrifugally driven jets, we find that for (1) less diffusive disks, (2) a stronger magnetic field, (3) a low poloidal diffusivity, or (4) a lower numerical diffusivity (resolution), the mass loading of the outflow is increased—resulting in more powerful jets with high-mass flux. For weak magnetization, the (weak) outflow is driven by the magnetic pressure gradient. We consider in detail the advection and diffusion of magnetic flux within the disk and we find that the disk and outflow magnetization may substantially change in time. This may have severe impact on the launching and formation process—an initially highly magnetized disk may evolve into a disk of weak magnetization which cannot drive strong outflows. We further investigate the jet asymptotic velocity and the jet rotational velocity in respect of the different launching scenarios. We find a lower degree of jet collimation than previous studies, most probably due to our revised outflow boundary condition.

Modern theoretical models of astrophysical jets combine accretion, rotation, and magnetic fields to launch and collimate supersonic flows from a central source. Near the source, magnetic field strengths must be large enough to collimate the jet requiring that the Poynting flux exceeds the kinetic energy flux. The extent to which the Poynting flux dominates kinetic energy flux at large distances from the engine distinguishes two classes of models. In magneto-centrifugal launch models, magnetic fields dominate only at scales ≲ 100 engine radii, after which the jets become hydrodynamically dominated (HD). By contrast, in Poynting flux dominated (PFD) magnetic tower models, the field dominates even out to much larger scales. To compare the large distance propagation differences of these two paradigms, we perform three-dimensional ideal magnetohydrodynamic adaptive mesh refinement simulations of both HD and PFD stellar jets formed via the same energy flux. We also compare how thermal energy losses and rotation of the jet base affects the stability in these jets. For the conditions described, we show that PFD and HD exhibit observationally distinguishable features: PFD jets are lighter, slower, and less stable than HD jets. Unlike HD jets, PFD jets develop current-driven instabilities that are exacerbated as cooling and rotation increase, resulting in jets that are clumpier than those in the HD limit. Our PFD jet simulations also resemble the magnetic towers that have been recently created in laboratory astrophysical jet experiments.

We address a primary question regarding the physical mechanism that triggers the energy release and initiates the onset of eruptions in the magnetar magnetosphere. Self-consistent stationary, axisymmetric models of the magnetosphere are constructed based on force-free magnetic field configurations that contain a helically twisted force-free flux rope. Depending on the surface magnetic field polarity, there exist two kinds of magnetic field configurations, inverse and normal. For these two kinds of configurations, variations of the flux rope equilibrium height in response to gradual surface physical processes, such as flux injections and crust motions, are carefully examined. We find that equilibrium curves contain two branches: one represents a stable equilibrium branch, and the other an unstable equilibrium branch. As a result, the evolution of the system shows a catastrophic behavior: when the magnetar surface magnetic field evolves slowly, the height of the flux rope would gradually reach a critical value beyond which stable equilibriums can no longer be maintained. Subsequently, the flux rope would lose equilibrium and the gradual quasi-static evolution of the magnetosphere will be replaced by a fast dynamical evolution. In addition to flux injections, the relative motion of active regions would give rise to the catastrophic behavior and lead to magnetic eruptions as well. We propose that a gradual process could lead to a sudden release of magnetosphere energy on a very short dynamical timescale, without being initiated by a sudden fracture in the crust of the magnetar. Some implications of our model are also discussed.

We report on an observation of SGR 1627−41 made with the Chandra X-Ray Observatory on 2011 June 16. Approximately three years after its outburst activity in 2008, the source's flux has been declining, as it approaches its quiescent state. For an assumed power-law spectrum, we find that the absorbed 2–10 keV flux for the source is 1.0^+0.3_{− 0.2} × 10⁻¹³ erg cm⁻² s⁻¹ with a photon index of 2.9 ± 0.8 (N_H = 1.0 × 10²³ cm⁻²). This flux is approximately consistent with that measured at the same time after the source's outburst in 1998. With measurements spanning three years after the 2008 outburst, we analyze the long-term flux and spectral evolution of the source. The flux evolution is well described by a double exponential with decay times of 0.5 ± 0.1 and 59 ± 6 days, and a thermal cooling model fit suggests that SGR 1627−41 may have a hot core (T_c ∼ 2 × 10⁸ K). We find no clear correlation between flux and spectral hardness as found in other magnetars. We consider the quiescent X-ray luminosities of magnetars and the subset of rotation-powered pulsars with high magnetic fields (B ≳ 10¹³ G) in relation to their spin-inferred surface magnetic field strength and find a possible trend between the two quantities.

We perform hydrodynamic supernova (SN) simulations in spherical symmetry for over 100 single stars of solar metallicity to explore the progenitor-explosion and progenitor-remnant connections established by the neutrino-driven mechanism. We use an approximative treatment of neutrino transport and replace the high-density interior of the neutron star (NS) by an inner boundary condition based on an analytic proto-NS core-cooling model, whose free parameters are chosen such that explosion energy, nickel production, and energy release by the compact remnant of progenitors around 20 M_☉ are compatible with SN 1987A. Thus, we are able to simulate the accretion phase, initiation of the explosion, subsequent neutrino-driven wind phase for 15–20 s, and the further evolution of the blast wave for hours to days until fallback is completed. Our results challenge long-standing paradigms. We find that remnant mass, launch time, and properties of the explosion depend strongly on the stellar structure and exhibit large variability even in narrow intervals of the progenitors' zero-age main-sequence mass. While all progenitors with masses below ∼15 M_☉ yield NSs, black hole (BH) as well as NS formation is possible for more massive stars, where partial loss of the hydrogen envelope leads to weak reverse shocks and weak fallback. Our NS baryonic masses of ∼1.2–2.0 M_☉ and BH masses >6 M_☉ are compatible with a possible lack of low-mass BHs in the empirical distribution. Neutrino heating accounts for SN energies between some 10⁵⁰ erg and ∼2 × 10⁵¹ erg but can hardly explain more energetic explosions and nickel masses higher than 0.1–0.2 M_☉. These seem to require an alternative SN mechanism.

We use a sample of 45 core collapse supernovae detected with the Advanced Camera for Surveys on board the Hubble Space Telescope to derive the core collapse supernova rate in the redshift range 0.1 < z < 1.3. In redshift bins centered on 〈z〉 = 0.39, 〈z〉 = 0.73, and 〈z〉 = 1.11, we find rates of 3.00^+1.28_{− 0.94}^+1.04_{− 0.57}, 7.39^+1.86_{− 1.52}^+3.20_{− 1.60}, and 9.57^+3.76_{− 2.80}^+4.96_{− 2.80}, respectively, given in units of yr⁻¹ Mpc⁻³ 10⁻⁴ h³₇₀. The rates have been corrected for host galaxy extinction, including supernovae missed in highly dust-enshrouded environments in infrared bright galaxies. The first errors are statistical while the second ones are the estimated systematic errors. We perform a detailed discussion of possible sources of systematic errors and note that these start to dominate over statistical errors at z > 0.5, emphasizing the need to better control the systematic effects. For example, a better understanding of the amount of dust extinction in the host galaxies and knowledge of the supernova luminosity function, in particular the fraction of faint M ≳ −15 supernovae, is needed to better constrain the rates. When comparing our results with the core collapse supernova rate based on the star formation rate, we find a good agreement, consistent with the supernova rate following the star formation rate, as expected.

In our Sun, the magnetic cycle is driven by the dynamo action occurring inside the convection zone, beneath the surface. Rotation couples with plasma turbulent motions to produce organized magnetic fields that erupt at the surface and undergo relatively regular cycles of polarity reversal. Among others, the axisymmetric dynamo models have been proved to be a quite useful tool to understand the dynamical processes responsible for the evolution of the solar magnetic cycle and the formation of the sunspots. Here, we discuss the role played by the radial density stratification on the critical layers of the Sun on the solar dynamo. The current view is that a polytropic description of the density stratification from beneath the tachocline region up to the Sun's surface is sufficient for the current precision of axisymmetric dynamo models. In this work, by using an up-to-date density profile obtained from a standard solar model, which is itself consistent with helioseismic data, we show that the detailed peculiarities of the density in critical regions of the Sun's interior, such as the tachocline, the base of the convection zone, the layers of partial ionization of hydrogen and helium, and the super-adiabatic layer, play a non-negligible role on the evolution of the solar magnetic cycle. Furthermore, we found that the chemical composition of the solar model plays a minor role in the formation and evolution of the solar magnetic cycle.

One of the leading models for electron acceleration in solar flares is stochastic acceleration by weakly turbulent fast magnetosonic waves ("fast waves"). In this model, large-scale flows triggered by magnetic reconnection excite large-wavelength fast waves, and fast-wave energy then cascades from large wavelengths to small wavelengths. Electron acceleration by large-wavelength fast waves is weak, and so the model relies on the small-wavelength waves produced by the turbulent cascade. In order for the model to work, the energy cascade time for large-wavelength fast waves must be shorter than the time required for the waves to propagate out of the solar-flare acceleration region. To investigate the effects of wave escape, we solve the wave kinetic equation for fast waves in weak turbulence theory, supplemented with a homogeneous wave-loss term. We find that the amplitude of large-wavelength fast waves must exceed a minimum threshold in order for a significant fraction of the wave energy to cascade to small wavelengths before the waves leave the acceleration region. We evaluate this threshold as a function of the dominant wavelength of the fast waves that are initially excited by reconnection outflows.

We analyze the temperature and EUV line emission of a coronal cavity and surrounding streamer in terms of a morphological forward model. We use a series of iron line ratios observed with the Hinode Extreme-ultraviolet Imaging Spectrograph (EIS) on 2007 August 9 to constrain temperature as a function of altitude in a morphological forward model of the streamer and cavity. We also compare model predictions to the EIS EUV line intensities and polarized brightness (pB) data from the Mauna Loa Solar Observatory (MLSO) Mark 4 K-coronameter. This work builds on earlier analysis using the same model to determine geometry of and density in the same cavity and streamer. The fit to the data with altitude-dependent temperature profiles indicates that both the streamer and cavity have temperatures in the range 1.4–1.7 MK. However, the cavity exhibits substantial substructure such that the altitude-dependent temperature profile is not sufficient to completely model conditions in the cavity. Coronal prominence cavities are structured by magnetism so clues to this structure are to be found in their plasma properties. These temperature substructures are likely related to structures in the cavity magnetic field. Furthermore, we find that the model overestimates the EUV line intensities by a factor of 4–10, without overestimating pB. We discuss this difference in terms of filling factors and uncertainties in density diagnostics and elemental abundances.

A self-consistent model of the interstellar pickup protons, the slab component of the Alfvénic turbulence, and core solar wind (SW) protons is presented for r ⩾ 1 along with the initial results of and comparison with the Voyager 2 (V2) observations. Two kinetic equations are used for the pickup proton distribution and Alfvénic power spectral density, and a third equation governs SW temperature including source due to the Alfvén wave energy dissipation. A fraction of the pickup proton free energy, f_D, which is actually released in the waveform during isotropization, is taken from the quasi-linear consideration without preexisting turbulence, whereas we use observations to specify the strength of the large-scale driving, C_sh, for turbulence. The main conclusions of our study can be summarized as follows. (1) For C_sh ≈ 1–1.5 and f_D ≈ 0.7–1, the model slab component agrees well with the V2 observations of the total transverse magnetic fluctuations starting from ∼8 AU. This indicates that the slab component at low-latitudes makes up a majority of the transverse magnetic fluctuations beyond 8–10 AU. (2) The model core SW temperature agrees well with the V2 observations for r ≳ 20 AU if f_D ≈ 0.7–1. (3) A combined effect of the Wentzel–Kramers–Brillouin attenuation, large-scale driving, and pickup proton generated waves results in the energy sink in the region r ≲ 10 AU, while wave energy is pumped in the turbulence beyond 10 AU. Without energy pumping, the nonlinear energy cascade is suppressed for r ≲ 10 AU, supplying only a small energy fraction into the k-region of dissipation by the core SW protons. A similar situation takes place for the two-dimensional turbulence. (4) The energy source due to the resonant Alfvén wave damping by the core SW protons is small at heliocentric distances r ≲ 10 AU for both the slab and the two-dimensional turbulent components. As a result, adiabatic cooling mostly controls the model SW temperature in this region, and the model temperature disagrees with the V2 observations in the region r ≲ 20 AU.

The radial dependence of particle peak fluxes in large solar energetic particle (SEP) events is important in determining the potential impact of space weather hazards on space missions. Using the Particle Acceleration and Transport in the Heliosphere code, we model the acceleration and transport of protons and iron ions at evolving coronal mass ejection shocks propagating throughout the inner heliosphere from about 0.1 to 2.5 AU. An example shock with a compression ratio of 3.9 and a speed of 1000 km s⁻¹ close to the Sun is modeled using a two-dimensional MHD ZEUS code. The compression ratio and shock speed weakened to 2.3 and 630 km s⁻¹, correspondingly, at 2 AU. Shocks with 15°, 45°, and 75° angles between the upstream magnetic field and the shock normal were studied. The shock angle was kept constant throughout the simulation. Both gradual and impulsive events are studied. Diffusive shock acceleration is assumed at the shock and we use a total diffusion coefficient that includes a parallel diffusion coefficient which takes into account the upstream wave amplification, and a perpendicular diffusion coefficient which is based on the NonLinear Guiding Center theory. The transport of particles escaping from the shock is modeled using a Monte Carlo approach. Time-intensity profiles for protons and iron ions are obtained. We analyzed the radial dependence of peak fluxes (J) for both protons and iron ions from 0.5 to 2 AU. We find that the functional dependence is softer than R⁻³ and is about R^−2.9 to R^−1.8 in the energy range of 0.3–5 MeV nuc⁻¹. Quasi-perpendicular shock showed a steeper radial dependence than a quasi-parallel shock. Mixed events show a softer radial dependence at energies above 500 keV nuc⁻¹ for iron ions and above 1 MeV for protons. The values of J(R) depend on seed particle composition, particle energy, shock obliquity, and the interplanetary turbulence level. Consequently, we advocate using SEP event-specific computer modeling rather than empirical formulae for future forecasting of the radiation environment throughout the heliosphere during large SEP events.

A leading formation scenario for R Coronae Borealis (RCB) stars invokes the merger of degenerate He and CO white dwarfs (WDs) in a binary. The observed ratio of ¹⁶O/¹⁸O for RCB stars is in the range of 0.3–20 much smaller than the solar value of ∼500. In this paper, we investigate whether such a low ratio can be obtained in simulations of the merger of a CO and a He WD. We present the results of five three-dimensional hydrodynamic simulations of the merger of a double WD system where the total mass is 0.9 M_☉ and the initial mass ratio (q) varies between 0.5 and 0.99. We identify in simulations with q ≲ 0.7 a feature around the merged stars where the temperatures and densities are suitable for forming ¹⁸O. However, more ¹⁶O is being dredged up from the C- and O-rich accretor during the merger than the amount of ¹⁸O that is produced. Therefore, on the dynamical timescale over which our hydrodynamics simulation runs, an ¹⁶O/¹⁸O ratio of ∼2000 in the "best" case is found. If the conditions found in the hydrodynamic simulations persist for 10⁶ s the oxygen ratio drops to 16 in one case studied, while in a hundred years it drops to ∼4 in another case studied, consistent with the observed values in RCB stars. Therefore, the merger of two WDs remains a strong candidate for the formation of these enigmatic stars.

Magnetic flux redistribution lies at the heart of the problem of star formation in dense cores of molecular clouds that are magnetized to a realistic level. If all of the magnetic flux of a typical core were to be dragged into the central star, the stellar field strength would be orders of magnitude higher than the observed values. This well-known magnetic flux problem can in principle be resolved through non-ideal MHD effects. Two-dimensional (axisymmetric) calculations have shown that ambipolar diffusion, in particular, can transport magnetic flux outward relative to matter, allowing material to enter the central object without dragging the field lines along. We show through simulations that such axisymmetric protostellar accretion flows are unstable in three dimensions to magnetic interchange instability in the azimuthal direction. The instability is driven by the magnetic flux redistributed from the matter that enters the central object. It typically starts to develop during the transition from the prestellar phase of star formation to the protostellar mass accretion phase. In the latter phase, the magnetic flux is transported outward mainly through advection by strongly magnetized low-density regions that expand against the collapsing inflow. The tussle between the gravity-driven infall and magnetically driven expansion leads to a highly filamentary inner accretion flow that is more disordered than previously envisioned. The efficient outward transport of magnetic flux by advection lowers the field strength at small radii, making the magnetic braking less efficient and the formation of rotationally supported disks easier in principle. However, we find no evidence for such disks in any of our rotating collapse simulations. We conclude that the inner protostellar accretion flow is shaped to a large extent by the flux redistribution-driven magnetic interchange instability. How disks form in such an environment is unclear.

Deep Hubble Space Telescope broadband images taken with Advanced Camera for Surveys (ACS) and WFPC2 of the giant (∼1000 AU diameter) dark silhouette proplyd 114-426 in the Orion Nebula show that this system is tilted, asymmetric, warped, and photoevaporated. The exquisite angular resolution of ACS allows us to map the distribution of dust grains at the northern translucent edge of the disk, dominated by the photoevaporative flow. Using the Mie theory for standard circumstellar disk grains, we find evidence for a spatial gradient in grain size. The typical dust radius ≃ 0.2–0.7 μm (less than what was reported by previous studies) becomes smaller as the distance from the disk center increases, consistent with the expectations for the dynamic of dust entrained in a gaseous photoevaporative wind. Our analysis of the disk morphology and location within the nebula indicates that this system is photoevaporated by the diffuse radiation field of the Orion Nebula, while being shielded from the radiation coming directly from the central Trapezium stars. We estimate the mass-loss rate from the disk surface and the timescale for total disk dissipation, which turns out to be of the order of 10⁴ yr. Such a short time, of the order of 1/100 of the cluster age, indicates that this system is seen on the verge of destruction. This is compatible with the exceptional nature of the disk, namely its combination of huge size and low mass. Finally, we briefly discuss the viability of possible mechanisms that may lead to the peculiar morphology of this system: external UV flux, binary star, and past close encounter.

The optical [N i] doublet near 5200 Å is anomalously strong in a variety of emission-line objects. We compute a detailed photoionization model and use it to show that pumping by far-ultraviolet (FUV) stellar radiation previously posited as a general explanation applies to the Orion Nebula (M42) and its companion M43; but, it is unlikely to explain planetary nebulae and supernova remnants. Our models establish that the observed nearly constant equivalent width of [N i] with respect to the dust-scattered stellar continuum depends primarily on three factors: the FUV to visual-band flux ratio of the stellar population, the optical properties of the dust, and the line broadening where the pumping occurs. In contrast, the intensity ratio [N i]/Hβ depends primarily on the FUV to extreme-ultraviolet ratio, which varies strongly with the spectral type of the exciting star. This is consistent with the observed difference of a factor of five between M42 and M43, which are excited by an O7 and B0.5 star, respectively. We derive a non-thermal broadening of order 5 km s⁻¹ for the [N i] pumping zone and show that the broadening mechanism must be different from the large-scale turbulent motions that have been suggested to explain the line widths in this H ii region. A mechanism is required that operates at scales of a few astronomical units, which may be driven by thermal instabilities of neutral gas in the range 1000–3000 K. In an Appendix A, we describe how collisional and radiative processes are treated in the detailed model N i atom now included in the Cloudy plasma code.

In order to understand the climate on terrestrial planets orbiting nearby Sun-like stars, one would like to know their thermal inertia. We use a global climate model to simulate the thermal phase variations of Earth analogs and test whether these data could distinguish between planets with different heat storage and heat transport characteristics. In particular, we consider a temperate climate with polar ice caps (like the modern Earth) and a snowball state where the oceans are globally covered in ice. We first quantitatively study the periodic radiative forcing from, and climatic response to, rotation, obliquity, and eccentricity. Orbital eccentricity and seasonal changes in albedo cause variations in the global-mean absorbed flux. The responses of the two climates to these global seasons indicate that the temperate planet has 3× the bulk heat capacity of the snowball planet due to the presence of liquid water oceans. The obliquity seasons in the temperate simulation are weaker than one would expect based on thermal inertia alone; this is due to cross-equatorial oceanic and atmospheric energy transport. Thermal inertia and cross-equatorial heat transport have qualitatively different effects on obliquity seasons, insofar as heat transport tends to reduce seasonal amplitude without inducing a phase lag. For an Earth-like planet, however, this effect is masked by the mixing of signals from low thermal inertia regions (sea ice and land) with that from high thermal inertia regions (oceans), which also produces a damped response with small phase lag. We then simulate thermal light curves as they would appear to a high-contrast imaging mission (TPF-I/Darwin). In order of importance to the present simulations, which use modern-Earth orbital parameters, the three drivers of thermal phase variations are (1) obliquity seasons, (2) diurnal cycle, and (3) global seasons. Obliquity seasons are the dominant source of phase variations for most viewing angles. A pole-on observer would measure peak-to-trough amplitudes of 13% and 47% for the temperate and snowball climates, respectively. Diurnal heating is important for equatorial observers (∼5% phase variations), because the obliquity effects cancel to first order from that vantage. Finally, we compare the prospects of optical versus thermal direct imaging missions for constraining the climate on exoplanets and conclude that while zero- and one-dimensional models are best served by thermal measurements, second-order models accounting for seasons and planetary thermal inertia would require both optical and thermal observations.

We provide evidence for a correlation between the presence of giant clumps and the occurrence of active galactic nuclei (AGNs) in disk galaxies. Giant clumps of 10⁸–10⁹ M_☉ arise from violent gravitational instability in gas-rich galaxies, and it has been proposed that this instability could feed supermassive black holes (BHs). We use emission line diagnostics to compare a sample of 14 clumpy (unstable) disks and a sample of 13 smoother (stable) disks at redshift z ∼ 0.7. The majority of clumpy disks in our sample have a high probability of containing AGNs. Their [O iii] λ5007 emission line is strongly excited, inconsistent with low-metallicity star formation (SF) alone. [Ne iii] λ3869 excitation is also higher. Stable disks rarely have such properties. Stacking ultra sensitive Chandra observations (4 Ms) reveals an X-ray excess in clumpy galaxies, which confirms the presence of AGNs. The clumpy galaxies in our intermediate-redshift sample have properties typical of gas-rich disk galaxies rather than mergers, being in particular on the main sequence of SF. This suggests that our findings apply to the physically similar and numerous gas-rich unstable disks at z > 1. Using the observed [O iii] and X-ray luminosities, we conservatively estimate that AGNs hosted by clumpy disks have typical bolometric luminosities of the order of a few 10⁴³ erg s⁻¹, BH growth rates $\dot{m}_{\rm BH} \sim 10^{-2}\,M_\odot$ yr⁻¹, and that these AGNs are substantially obscured in X-rays. This moderate-luminosity mode could provide a large fraction of today's BH mass with a high duty cycle (>10%), accretion bursts with higher luminosities being possible over shorter phases. Violent instabilities at high redshift (giant clumps) are a much more efficient driver of BH growth than the weak instabilities in nearby spirals (bars), and the evolution of disk instabilities with mass and redshift could explain the simultaneous downsizing of SF and of BH growth.

We present an analysis of the evolution of the central mass-density profile of massive elliptical galaxies from the SLACS and BELLS strong gravitational lens samples over the redshift interval z ≈ 0.1–0.6, based on the combination of strong-lensing aperture mass and stellar velocity-dispersion constraints. We find a significant trend toward steeper mass profiles (parameterized by the power-law density model with ρ∝r^−γ) at later cosmic times, with magnitude d < γ > /dz = −0.60 ± 0.15. We show that the combined lens-galaxy sample is consistent with a non-evolving distribution of stellar velocity dispersions. Considering possible additional dependence of <γ > on lens-galaxy stellar mass, effective radius, and Sérsic index, we find marginal evidence for shallower mass profiles at higher masses and larger sizes, but with a significance that is subdominant to the redshift dependence. Using the results of published Monte Carlo simulations of spectroscopic lens surveys, we verify that our mass-profile evolution result cannot be explained by lensing selection biases as a function of redshift. Interpreted as a true evolutionary signal, our result suggests that major dry mergers involving off-axis trajectories play a significant role in the evolution of the average mass-density structure of massive early-type galaxies over the past 6 Gyr. We also consider an alternative non-evolutionary hypothesis based on variations in the strong-lensing measurement aperture with redshift, which would imply the detection of an "inflection zone" marking the transition between the baryon-dominated and dark-matter halo-dominated regions of the lens galaxies. Further observations of the combined SLACS+BELLS sample can constrain this picture more precisely, and enable a more detailed investigation of the multivariate dependences of galaxy mass structure across cosmic time.

The Blanco Cosmology Survey (BCS) is a 60 night imaging survey of ∼80 deg² of the southern sky located in two fields: (α, δ) = (5 hr, −55°) and (23 hr, −55°). The survey was carried out between 2005 and 2008 in griz bands with the Mosaic2 imager on the Blanco 4 m telescope. The primary aim of the BCS survey is to provide the data required to optically confirm and measure photometric redshifts for Sunyaev–Zel'dovich effect selected galaxy clusters from the South Pole Telescope and the Atacama Cosmology Telescope. We process and calibrate the BCS data, carrying out point-spread function-corrected model-fitting photometry for all detected objects. The median 10σ galaxy (point-source) depths over the survey in griz are approximately 23.3 (23.9), 23.4 (24.0), 23.0 (23.6), and 21.3 (22.1), respectively. The astrometric accuracy relative to the USNO-B survey is ∼45 mas. We calibrate our absolute photometry using the stellar locus in grizJ bands, and thus our absolute photometric scale derives from the Two Micron All Sky Survey, which has ∼2% accuracy. The scatter of stars about the stellar locus indicates a systematic floor in the relative stellar photometric scatter in griz that is ∼1.9%, ∼2.2%, ∼2.7%, and ∼2.7%, respectively. A simple cut in the AstrOmatic star–galaxy classifier spread_model produces a star sample with good spatial uniformity. We use the resulting photometric catalogs to calibrate photometric redshifts for the survey and demonstrate scatter δz/(1 + z) = 0.054 with an outlier fraction η < 5% to z ∼ 1. We highlight some selected science results to date and provide a full description of the released data products.

We analyze line-of-sight atomic hydrogen (H i) line profiles of 31 nearby, low-mass galaxies selected from the Very Large Array—ACS Nearby Galaxy Survey Treasury (VLA-ANGST) and The H i Nearby Galaxy Survey (THINGS) to trace regions containing cold (T ≲ 1400 K) H i from observations with a uniform linear scale of 200 pc beam⁻¹. Our galaxy sample spans four orders of magnitude in total H i mass and nine magnitudes in M_B. We fit single and multiple component functions to each spectrum to isolate the cold, neutral medium given by a low-dispersion (<6 km s⁻¹) component of the spectrum. Most H i spectra are adequately fit by a single Gaussian with a dispersion of 8–12 km s⁻¹. Cold H i is found in 23 of 27 (∼85%) galaxies after a reduction of the sample size due to quality-control cuts. The cold H i contributes ∼20% of the total line-of-sight flux when found with warm H i. Spectra best fit by a single Gaussian, but dominated by cold H i emission (i.e., have velocity dispersions of <6 km s⁻¹), are found primarily beyond the optical radius of the host galaxy. The cold H i is typically found in localized regions and is generally not coincident with the very highest surface density peaks of the global H i distribution (which are usually areas of recent star formation). We find a lower limit for the mass fraction of cold-to-total H i gas of only a few percent in each galaxy.

We demonstrate that dwarf galaxies (10⁷ < M_stellar < 10⁹ M_☉, −12 > M_r > −18) with no active star formation are extremely rare (<0.06%) in the field. Our sample is based on the NASA-Sloan Atlas which is a reanalysis of the Sloan Digital Sky Survey Data Release 8. We examine the relative number of quenched versus star-forming dwarf galaxies, defining quenched galaxies as having no Hα emission (EW_Hα < 2 Å) and a strong 4000 Å break. The fraction of quenched dwarf galaxies decreases rapidly with increasing distance from a massive host, leveling off for distances beyond 1.5 Mpc. We define galaxies beyond 1.5 Mpc of a massive host galaxy to be in the field. We demonstrate that there is a stellar mass threshold of M_stellar < 1.0 × 10⁹ M_☉ below which quenched galaxies do not exist in the field. Below this threshold, we find that none of the 2951 field dwarf galaxies are quenched; all field dwarf galaxies show evidence for recent star formation. Correcting for volume effects, this corresponds to a 1σ upper limit on the quenched fraction of 0.06%. In more dense environments, quenched galaxies account for 23% of the dwarf population over the same stellar mass range. The majority of quenched dwarf galaxies (often classified as dwarf elliptical galaxies) are within 2 virial radii of a massive galaxy, and only a few percent of quenched dwarf galaxies exist beyond 4 virial radii. Thus, for galaxies with stellar mass less than 1.0 × 10⁹ M_☉, ending star formation requires the presence of a more massive neighbor, providing a stringent constraint on models of star formation feedback.

Using a spectral decomposition technique, we investigate the physical origin of the high-velocity emission-line gas in a sample of 39 gas-rich, ultraluminous infrared galaxy mergers. Regions with shock-like excitation were identified in two kinematically distinct regimes, characterized by broad (σ > 150 km s⁻¹) and narrow linewidths (σ ⩽ 150 km s⁻¹). Here, we investigate the physical origin of the broad emission, which we show is predominantly excited by shocks with velocities of 200–300 km s⁻¹. Considering the large amount of extinction in these galaxies, the blueshift of the broad emission suggests an origin on the near side of the galaxy and therefore an interpretation as a galactic outflow. The large spatial extent of the broad, shocked emission component is generally inconsistent with an origin in the narrow-line region of an active galactic nucleus. The kinetic energy in the mass loss as well as the luminosity of the emission lines is consistent with the fraction of the supernova energy attributed to these mechanisms by shocked stellar winds. Since some shocks can be recognized in moderately high resolution, integrated spectra of nearby ultraluminous starbursts, the spectral fitting technique introduced in Soto & Martin may therefore be used to improve the accuracy of the physical properties measured for high-redshift galaxies from their (observed frame) infrared spectra.

Through numerical simulations, we study the dissolution timescale of the Ursa Minor cold stellar clump, due to the combination of phase-mixing and gravitational encounters with compact dark substructures in the halo of Ursa Minor. We compare two scenarios: one where the dark halo is made up by a smooth mass distribution of light particles and one where the halo contains 10% of its mass in the form of substructures (subhalos). In a smooth halo, the stellar clump survives for a Hubble time provided that the dark matter halo has a large core. In contrast, when the point-mass dark substructures are added, the clump survives for barely ∼1.5 Gyr. These results suggest a strong test of the Λ-cold dark matter scenario at dwarf galaxy scale.

We reanalyze the Fermi spectra of the Geminga and Vela pulsars. We find that the spectrum of Geminga above the break is well approximated by a simple power law without the exponential cutoff, making Geminga's spectrum similar to that of Crab. Vela's broadband γ-ray spectrum is equally well fit with both the exponential cutoff and the double power-law shapes. In the broadband double power-law fits, for a typical Fermi spectrum of a bright γ-ray pulsar, most of the errors accumulate due to the arbitrary parameterization of the spectral roll-off. In addition, a power law with an exponential cutoff gives an acceptable fit for the underlying double power-law spectrum for a very broad range of parameters, making such fitting procedures insensitive to the underlying Fermi photon spectrum. Our results have important implications for the mechanism of pulsar high-energy emission. A number of observed properties of γ-ray pulsars—i.e., the broken power-law spectra without exponential cutoffs and stretching in the case of Crab beyond the maximal curvature limit, spectral breaks close to or exceeding the maximal breaks due to curvature emission, patterns of the relative intensities of the leading and trailing pulses in the Crab repeated in the X-ray and γ-ray regions, presence of profile peaks at lower energies aligned with γ-ray peaks—all point to the inverse Compton origin of the high-energy emission from majority of pulsars.

We present two millisecond pulsar discoveries from the PALFA survey of the Galactic plane with the Arecibo telescope. PSR J1955+2527 is an isolated pulsar with a period of 4.87 ms, and PSR J1949+3106 has a period of 13.14 ms and is in a 1.9 day binary system with a massive companion. Their timing solutions, based on 4 years of timing measurements with the Arecibo, Green Bank, Nançay, and Jodrell Bank telescopes, allow precise determination of spin and astrometric parameters, including precise determinations of their proper motions. For PSR J1949+3106, we can clearly detect the Shapiro delay. From this we measure the pulsar mass to be 1.47^+0.43_{− 0.31} M_☉, the companion mass to be 0.85^+0.14_{− 0.11} M_☉, and the orbital inclination to be i = 79.9^−1.9_{+ 1.6} deg, where uncertainties correspond to ±1σ confidence levels. With continued timing, we expect to also be able to detect the advance of periastron for the J1949+3106 system. This effect, combined with the Shapiro delay, will eventually provide very precise mass measurements for this system and a test of general relativity.

We present the discovery and phase-coherent timing of four highly dispersed millisecond pulsars (MSPs) from the Arecibo PALFA Galactic plane survey: PSRs J1844+0115, J1850+0124, J1900+0308, and J1944+2236. Three of the four pulsars are in binary systems with low-mass companions, which are most likely white dwarfs, and which have orbital periods on the order of days. The fourth pulsar is isolated. All four pulsars have large dispersion measures (DM >100 pc cm⁻³), are distant (≳ 3.4 kpc), faint at 1.4 GHz (≲ 0.2 mJy), and are fully recycled (with spin periods P between 3.5 and 4.9 ms). The three binaries also have very small orbital eccentricities, as expected for tidally circularized, fully recycled systems with low-mass companions. These four pulsars have DM/P ratios that are among the highest values for field MSPs in the Galaxy. These discoveries bring the total number of confirmed MSPs from the PALFA survey to 15. The discovery of these MSPs illustrates the power of PALFA for finding weak, distant MSPs at low-Galactic latitudes. This is important for accurate estimates of the Galactic MSP population and for the number of MSPs that the Square Kilometer Array can be expected to detect.

It is firmly established that the stellar mass distribution is smooth, covering the range 0.1–100 M_☉. It is to be expected that the masses of the ensuing compact remnants correlate with the masses of their progenitor stars, and thus it is generally thought that the remnant masses should be smoothly distributed from the lightest white dwarfs to the heaviest black holes (BHs). However, this intuitive prediction is not borne out by observed data. In the rapidly growing population of remnants with observationally determined masses, a striking mass gap has emerged at the boundary between neutron stars (NSs) and BHs. The heaviest NSs reach a maximum of two solar masses, while the lightest BHs are at least five solar masses. Over a decade after the discovery, the gap has become a significant challenge to our understanding of compact object formation. We offer new insights into the physical processes that bifurcate the formation of remnants into lower-mass NSs and heavier BHs. Combining the results of stellar modeling with hydrodynamic simulations of supernovae, we both explain the existence of the gap and also put stringent constraints on the inner workings of the supernova explosion mechanism. In particular, we show that core-collapse supernovae are launched within 100–200 ms of the initial stellar collapse, implying that the explosions are driven by instabilities with a rapid (10–20 ms) growth time. Alternatively, if future observations fill in the gap, this will be an indication that these instabilities develop over a longer (>200 ms) timescale.

The probability of occurrence of extreme solar particle events (SPEs) with proton fluence (>30 MeV) F₃₀ ⩾ 10¹⁰ cm⁻² is evaluated based on data on the cosmogenic isotopes ¹⁴C and ¹⁰Be in terrestrial archives covering centennial–millennial timescales. Four potential candidates with F₃₀ = (1–1.5) × 10¹⁰ cm⁻² and no events with F₃₀ > 2 × 10¹⁰ cm⁻² are identified since 1400 AD in the annually resolved ¹⁰Be data. A strong SPE related to the Carrington flare of 1859 AD is not supported by the data. For the last 11,400 years, 19 SPE candidates with F₃₀ = (1–3) × 10¹⁰ cm⁻² are found and clearly no event with F₃₀ > 5 × 10¹⁰ cm⁻² (50 times the SPE of 1956 February 23) has occurred. These values serve as observational upper limits on the strength of SPEs on the timescale of tens of millennia. Two events, ca. 780 and 1460 AD, appear in different data series making them strong candidates for extreme SPEs. We build a distribution of the occurrence probability of extreme SPEs, providing a new strict observational constraint. Practical limits can be set as F₃₀ ≈ 1, 2–3, and 5×10¹⁰ cm⁻² for occurrence probabilities ≈10⁻², 10⁻³, and 10⁻⁴ yr⁻¹, respectively. Because of the uncertainties, our results should be interpreted as a conservative upper limit on the SPE occurrence near Earth. The mean solar energetic particle (SEP) flux is evaluated as ≈40 (cm² s)⁻¹, in agreement with estimates from lunar rocks. On average, extreme SPEs contribute about 10% to the total SEP fluence.

We have searched for evidence of significant shock acceleration of He ions of ∼1–10 MeV amu⁻¹ in situ at 258 interplanetary traveling shock waves observed by the Wind spacecraft. We find that the probability of observing significant acceleration, and the particle intensity observed, depends strongly upon the shock speed and less strongly upon the shock compression ratio. For most of the 39 fast shocks with significant acceleration, the observed spectral index agrees with either that calculated from the shock compression ratio or with the spectral index of the upstream background, when the latter spectrum is harder, as expected from diffusive shock theory. In many events the spectra are observed to roll downward at higher energies, as expected from Ellison–Ramaty and from Lee shock-acceleration theories. The dearth of acceleration at ∼85% of the shocks is explained by (1) a low shock speed, (2) a low shock compression ratio, and (3) a low value of the shock-normal angle with the magnetic field, which may cause the energy spectra that roll downward at energies below our observational threshold. Quasi-parallel shock waves are rarely able to produce measurable acceleration at 1 AU. The dependence of intensity on shock speed, seen here at local shocks, mirrors the dependence found previously for the peak intensities in large solar energetic-particle events upon speeds of the associated coronal mass ejections which drive the shocks.

We explore the spatio-temporal evolution of solar flares by fitting a radial expansion model r(t) that consists of an exponentially growing acceleration phase, followed by a deceleration phase that is parameterized by the generalized diffusion function r(t)∝κ(t − t₁)^β/2, which includes the logistic growth limit (β = 0), sub-diffusion (β = 0–1), classical diffusion (β = 1), super-diffusion (β = 1–2), and the linear expansion limit (β = 2). We analyze all M- and X-class flares observed with Geostationary Operational Environmental Satellite and Atmospheric Imaging Assembly/Solar Dynamics Observatory (SDO) during the first two years of the SDO mission, amounting to 155 events. We find that most flares operate in the sub-diffusive regime (β = 0.53 ± 0.27), which we interpret in terms of anisotropic chain reactions of intermittent magnetic reconnection episodes in a low plasma-β corona. We find a mean propagation speed of v = 15 ± 12 km s⁻¹, with maximum speeds of v_max = 80 ± 85 km s⁻¹ per flare, which is substantially slower than the sonic speeds expected for thermal diffusion of flare plasmas. The diffusive characteristics established here (for the first time for solar flares) is consistent with the fractal-diffusive self-organized criticality model, which predicted diffusive transport merely based on cellular automaton simulations.

Understanding changes in the solar flux over geologic time is vital for understanding the evolution of planetary atmospheres because it affects atmospheric escape and chemistry, as well as climate. We describe a numerical parameterization for wavelength-dependent changes to the non-attenuated solar flux appropriate for most times and places in the solar system. We combine data from the Sun and solar analogs to estimate enhanced UV and X-ray fluxes for the young Sun and use standard solar models to estimate changing visible and infrared fluxes. The parameterization, a series of multipliers relative to the modern top of the atmosphere flux at Earth, is valid from 0.1 nm through the infrared, and from 0.6 Gyr through 6.7 Gyr, and is extended from the solar zero-age main sequence to 8.0 Gyr subject to additional uncertainties. The parameterization is applied to a representative modern day flux, providing quantitative estimates of the wavelength dependence of solar flux for paleodates relevant to the evolution of atmospheres in the solar system (or around other G-type stars). We validate the code by Monte Carlo analysis of uncertainties in stellar age and flux, and with comparisons to the solar proxies κ¹ Cet and EK Dra. The model is applied to the computation of photolysis rates on the Archean Earth.

The variable magnetic field of the solar photosphere exhibits periodic reversals as a result of dynamo activity occurring within the solar interior. We decompose the surface field as observed by both the Wilcox Solar Observatory and the Michelson Doppler Imager into its harmonic constituents, and present the time evolution of the mode coefficients for the past three sunspot cycles. The interplay between the various modes is then interpreted from the perspective of general dynamo theory, where the coupling between the primary and secondary families of modes is found to correlate with large-scale polarity reversals for many examples of cyclic dynamos. Mean-field dynamos based on the solar parameter regime are then used to explore how such couplings may result in the various long-term trends in the surface magnetic field observed to occur in the solar case.

In this paper, we describe a theoretical model for accelerating an arbitrary upstream particle distribution. Only those particles that exceed a prescribed injection energy, E_inj, are accelerated via the diffusive shock acceleration (DSA) mechanism, also known as first-order Fermi acceleration. We identify a set of quasi-parallel shocks at 1 AU and use the observed solar wind particle distribution information to construct our upstream distribution, which is then accelerated diffusively at the shock, assuming the observed shock parameters. The injection energy for particles to be accelerated diffusively at a quasi-parallel shock is discussed theoretically. By using the observed upstream solar wind distribution function and the observed shock parameters, we can compute the injection energy that matches the observed downstream accelerated particle spectrum. Like the previous studies of van Nes et al., Lario et al., and Ho et al., this analysis focuses on the acceleration of protons only via the first-order Fermi acceleration mechanism. However, our primary focus is on quasi-parallel shocks and the injection mechanism in the context of DSA with a background thermal solar wind modeled as a Maxwellian or kappa distribution. Our approach allows for a direct test of injection at interplanetary shocks. It has been proposed that an additional seed population of energetic particles is needed to explain the accelerated particle distribution downstream of quasi-parallel shocks. This conclusion is based typically on studies that address the acceleration of heavy ions primarily and do not characterize the injection of protons alone using the DSA mechanism. Through comparisons of Maxwellian and kappa upstream distributions, we find that DSA with injection directly from a thermal Maxwellian distribution, or weak departures therefrom, for protons is responsible for energetic solar particle events associated with quasi-parallel shocks.

We investigate the influence of the geometry of the solar filament magnetic structure on the large-amplitude longitudinal oscillations. A representative filament flux tube is modeled as composed of a cool thread centered in a dipped part with hot coronal regions on either side. We have found the normal modes of the system and establish that the observed longitudinal oscillations are well described with the fundamental mode. For small and intermediate curvature radii and moderate to large density contrast between the prominence and the corona, the main restoring force is the solar gravity. In this full wave description of the oscillation a simple expression for the oscillation frequencies is derived in which the pressure-driven term introduces a small correction. We have also found that the normal modes are almost independent of the geometry of the hot regions of the tube. We conclude that observed large-amplitude longitudinal oscillations are driven by the projected gravity along the flux tubes and are strongly influenced by the curvature of the dips of the magnetic field in which the threads reside.

Accurately determining the properties of stars is of prime importance for characterizing stellar populations in our Galaxy. The field of asteroseismology has been thought to be particularly successful in such an endeavor for stars in different evolutionary stages. However, to fully exploit its potential, robust methods for estimating stellar parameters are required and independent verification of the results is mandatory. With this purpose, we present a new technique to obtain stellar properties by coupling asteroseismic analysis with the InfraRed Flux Method. By using two global seismic observables and multi-band photometry, the technique allows us to obtain masses, radii, effective temperatures, bolometric fluxes, and hence distances for field stars in a self-consistent manner. We apply our method to 22 solar-like oscillators in the Kepler short-cadence sample, that have accurate Hipparcos parallaxes. Our distance determinations agree to better than 5%, while measurements of spectroscopic effective temperatures and interferometric radii also validate our results. We briefly discuss the potential of our technique for stellar population analysis and models of Galactic Chemical Evolution.

We report the discovery of a wide (∼1400 AU projected separation), common proper motion companion to the nearby M dwarf LHS 2803 (PSO J207.0300–13.7422). This object was discovered during our census of the local T dwarf population using Pan-STARRS1 and Two Micron All Sky Survey data. Using the Infrared Telescope Facility/SpeX near-infrared spectroscopy, we classify the secondary to be spectral type T5.5. University of Hawaii 2.2 m/SuperNova Integral Field Spectrograph optical spectroscopy indicates that the primary has a spectral type of M4.5, with approximately solar metallicity and no measurable Hα emission. We use this lack of activity to set a lower age limit for the system of 3.5 Gyr. Using a comparison with chance alignments of brown dwarfs and nearby stars, we conclude that the two objects are unlikely to be a chance association. The primary's photometric distance of 21 pc and its proper motion implies thin disk kinematics. Based on these kinematics and its metallicity, we set an upper age limit for the system of 10 Gyr. Evolutionary model calculations suggest that the secondary has a mass of 72±⁴₇M_Jup, temperature of 1120 ± 80 K, and log g = 5.4 ± 0.1 dex. Model atmosphere fitting to the near-IR spectrum gives similar physical parameters of 1100 K and log g = 5.0.

Precise subtraction of foreground sources is crucial for detecting and estimating 21 cm H i signals from the Epoch of Reionization (EoR). We quantify how imperfect point-source subtraction due to limitations of the measurement data set yields structured residual signal in the data set. We use the Cramer–Rao lower bound, as a metric for quantifying the precision with which a parameter may be measured, to estimate the residual signal in a visibility data set due to imperfect point-source subtraction. We then propagate these residuals into two metrics of interest for 21 cm EoR experiments—the angular power spectrum and two-dimensional power spectrum—using a combination of full analytic covariant derivation, analytic variant derivation, and covariant Monte Carlo simulations. This methodology differs from previous work in two ways: (1) it uses information theory to set the point-source position error, rather than assuming a global rms error, and (2) it describes a method for propagating the errors analytically, thereby obtaining the full correlation structure of the power spectra. The methods are applied to two upcoming low-frequency instruments that are proposing to perform statistical EoR experiments: the Murchison Widefield Array and the Precision Array for Probing the Epoch of Reionization. In addition to the actual antenna configurations, we apply the methods to minimally redundant and maximally redundant configurations. We find that for peeling sources above 1 Jy, the amplitude of the residual signal, and its variance, will be smaller than the contribution from thermal noise for the observing parameters proposed for upcoming EoR experiments, and that optimal subtraction of bright point sources will not be a limiting factor for EoR parameter estimation. We then use the formalism to provide an ab initio analytic derivation motivating the "wedge" feature in the two-dimensional power spectrum, complementing previous discussion in the literature.

Individual dark matter halos in cosmological simulations vary widely in their detailed structural properties, properties such as concentration, shape, spin, and degree of internal relaxation. Recent non-parametric (principal component) analyses suggest that a few principal components explain a large fraction of the scatter in these structural properties. The main principal component is closely aligned with concentration, which in turn is known to be related to the mass accretion history (MAH) of the halo, as described by its merger tree. Here, we examine more generally the connection between the MAH and structural parameters. The space of mass accretion histories has principal components of its own. The strongest, accounting for almost 60% of the scatter between individual histories, can be interpreted as the age of the system. We give an analytic fit for this first component, which provides a rigorous way of defining the dynamical age of a halo. The second strongest component, representing acceleration or deceleration of growth at late times, accounts for 25% of the scatter. Relating structural parameters to formation history, we find that concentration correlates strongly with the early history of the halo, while shape and degree of relaxation or dynamical equilibrium correlate with the later history. We examine the inferences about formation history that can be drawn by splitting halos into sub-samples based on observable properties such as concentration and shape. Applications include the definition young and old samples of galaxy clusters in a quantitative way, or empirical tests of environmental processing rates in clusters.

The Small Magellanic Cloud (SMC) has surprisingly strong submillimeter- and millimeter-wavelength emission that is inconsistent with standard dust models, including those with emission from spinning dust. Here, we show that the emission from the SMC may be understood if the interstellar dust mixture includes magnetic nanoparticles, emitting magnetic dipole radiation resulting from thermal fluctuations in the magnetization. The magnetic grains can be metallic iron, magnetite Fe₃O₄, or maghemite γ-Fe₂O₃. The required mass of iron is consistent with elemental abundance constraints. The magnetic dipole emission is predicted to be polarized orthogonally to the normal electric dipole radiation if the nanoparticles are inclusions in larger grains. We speculate that other low-metallicity galaxies may also have a large fraction of the interstellar Fe in magnetic materials.

We present an analytic one-dimensional radiative–convective model of the thermal structure of planetary atmospheres. Our model assumes that thermal radiative transfer is gray and can be represented by the two-stream approximation. Model atmospheres are assumed to be in hydrostatic equilibrium, with a power-law scaling between the atmospheric pressure and the gray thermal optical depth. The convective portions of our models are taken to follow adiabats that account for condensation of volatiles through a scaling parameter to the dry adiabat. By combining these assumptions, we produce simple, analytic expressions that allow calculations of the atmospheric-pressure–temperature profile, as well as expressions for the profiles of thermal radiative flux and convective flux. We explore the general behaviors of our model. These investigations encompass (1) worlds where atmospheric attenuation of sunlight is weak, which we show tend to have relatively high radiative–convective boundaries; (2) worlds with some attenuation of sunlight throughout the atmosphere, which we show can produce either shallow or deep radiative–convective boundaries, depending on the strength of sunlight attenuation; and (3) strongly irradiated giant planets (including hot Jupiters), where we explore the conditions under which these worlds acquire detached convective regions in their mid-tropospheres. Finally, we validate our model and demonstrate its utility through comparisons to the average observed thermal structure of Venus, Jupiter, and Titan, and by comparing computed flux profiles to more complex models.

The observed properties of transiting exoplanets are an exceptionally rich source of information that allows us to understand and characterize their physical properties. Unfortunately, only a relatively small fraction of the known exoplanets discovered using the radial velocity technique are known to transit their host due to the stringent orbital geometry requirements. For each target, the transit probability and predicted transit time can be calculated to great accuracy with refinement of the orbital parameters. However, the transit probability of short period and eccentric orbits can have a reasonable time dependence due to the effects of apsidal and nodal precession, thus altering their transit potential and predicted transit time. Here we investigate the magnitude of these precession effects on transit probabilities and apply this to the known radial velocity exoplanets. We assess the refinement of orbital parameters as a path to measuring these precessions and cyclic transit probabilities.