Table of contents for issue 1, volume 742, The Astrophysical Journal

We present new 230 GHz Submillimeter Array observations of the candidate first hydrostatic core Per-Bolo 58. We report the detection of a 1.3 mm continuum source and a bipolar molecular outflow, both centered on the position of the candidate first hydrostatic core. The continuum detection has a total flux density of 26.6 ± 4.0 mJy, from which we calculate a total (gas and dust) mass of 0.11 ± 0.05 M_☉ and a mean number density of 2.0 ± 1.6 × 10⁷ cm⁻³. There is some evidence for the existence of an unresolved component in the continuum detection, but longer-baseline observations are required in order to confirm the presence of this component and determine whether its origin lies in a circumstellar disk or in the dense inner envelope. The bipolar molecular outflow is observed along a nearly due east–west axis. The outflow is slow (characteristic velocity of 2.9 km s⁻¹), shows a jet-like morphology (opening semi-angles ∼8° for both lobes), and extends to the edges of the primary beam. We calculate the kinematic and dynamic properties of the outflow in the standard manner and compare them to several other protostars and candidate first hydrostatic cores with similarly low luminosities. We discuss the evidence both in support of and against the possibility that Per-Bolo 58 is a first hydrostatic core, and we outline future work needed to further evaluate the evolutionary status of this object.

Up to now, no laboratory-based study has investigated polycyclic aromatic hydrocarbon (PAH) species as potential carriers of both the diffuse interstellar bands (DIBs) and the 2175 Å UV bump. We examined the proposed correlation between these two features by applying experimental and theoretical techniques on two specific medium-sized/large PAHs (dibenzorubicene C₃₀H₁₄ and hexabenzocoronene C₄₂H₁₈) in their neutral and cationic states. It was already shown that mixtures of sufficiently large, neutral PAHs can partly or even completely account for the UV bump. We investigated how the absorption bands are altered upon ionization of these molecules by interstellar UV photons. The experimental studies presented here were realized by performing matrix isolation spectroscopy with subsequent far-UV irradiation. The main effects were found to be a broadening of the absorption bands in the UV combined with slight redshifts. The position of the complete π–π* absorption structure around 217.5 nm, however, remains more or less unchanged, which could explain the observed position invariance of the interstellar bump for different lines of sight. This favors the assignment of this feature to the interstellar PAH population. As far as the DIBs are concerned, neither our investigations nor the laboratory studies carried out by other research groups support a possible connection with this class of molecules. Instead, there are reasonable arguments that neutral and singly ionized cationic PAHs cannot be held responsible for the DIBs.

We present an analysis of deep multiwavelength data for z ≈ 0.3–3 starburst galaxies selected by their 70 μm emission in the Extended-Chandra Deep Field-South and Extended Groth Strip. We identify active galactic nuclei (AGNs) in these infrared sources through their X-ray emission and quantify the fraction that host an AGN. We find that the fraction depends strongly on both the mid-infrared color and rest-frame mid-infrared luminosity of the source, rising to ∼50%–70% at the warmest colors (F_24 μm/F_70 μm ≲ 0.2) and highest mid-infrared luminosities (corresponding to ultraluminous infrared galaxies), similar to the trends found locally. Additionally, we find that the AGN fraction depends strongly on the star formation rate (SFR) of the host galaxy (inferred from the observed-frame 70 μm luminosity after subtracting the estimated AGN contribution), particularly for more luminous AGNs (L_{0.5 − 8.0keV} ≳ 10⁴³ erg s⁻¹). At the highest SFRs (∼1000 M_☉ yr⁻¹), the fraction of galaxies with an X-ray detected AGN rises to ≈30%, roughly consistent with that found in high-redshift submillimeter galaxies. Assuming that the AGN fraction is driven by the SFR (rather than stellar mass or redshift, for which our sample is largely degenerate), this result implies that the duty cycle of luminous AGN activity increases with the SFR of the host galaxy: specifically, we find that luminous X-ray detected AGNs are at least ∼5–10 times more common in systems with high SFRs (≳ 300 M_☉ yr⁻¹) than in systems with lower SFRs (≲ 30 M_☉ yr⁻¹). Lastly, we investigate the ratio between the supermassive black hole accretion rate (inferred from the AGN X-ray luminosity) and the bulge growth rate of the host galaxy (approximated as the SFR) and find that, for sources with detected AGNs and star formation (and neglecting systems with low star formation rates to which our data are insensitive), this ratio in distant starbursts agrees well with that expected from the local scaling relation assuming the black holes and bulges grew at the same epoch. These results imply that black holes and bulges grow together during periods of vigorous star formation and AGN activity.

We present an analysis of the extended emission around the anomalous X-ray pulsar 1E 1547.0−5408 using four XMM-Newton observations taken with the source in varying states of outburst as well as in quiescence. We find that the extended emission flux is highly variable and strongly correlated with the flux of the magnetar. Based on this result, as well as on spectral and energetic considerations, we conclude that the extended emission is dominated by a dust-scattering halo and not a pulsar wind nebula (PWN), as has been previously argued. We obtain an upper limit on the 2–10 keV flux of a possible PWN of 4.7 × 10⁻¹⁴ erg s⁻¹ cm⁻², three times less than the previously claimed value, implying an efficiency for conversion of spin-down energy into nebular luminosity of <9 × 10⁻⁴ (assuming a distance of 4 kpc). We do, however, find strong evidence for X-ray emission from the supernova remnant shell surrounding the pulsar, as previously reported.

The aggregation of dust through sticking collisions is the first step of planet formation. The basic physical properties of the evolving dust aggregates strongly depend on the porosity of the aggregates; e.g., mechanical strength, thermal conductivity, and the gas–grain coupling time. Also, the outcome of further collisions depends on the porosity of the colliding aggregates. In laboratory experiments we study the growth of large aggregates of ∼3 mm to 3 cm through continuous impacts of small dust agglomerates of 100 μm in size, consisting of μm grains at different impact velocities. The experiments show that agglomerates grow by direct sticking as well as through gravitational reaccretion. The latter can be regarded as a suitable analog to the reaccretion of fragments by gas drag in protoplanetary disks. Experiments were carried out in the velocity range between 1.5 m s⁻¹ and 7 m s⁻¹. With increasing impact velocities the volume filling factor of the resulting agglomerates increases from ϕ = 0.2 for 1.5 m s⁻¹ to ϕ = 0.32 for 7 m s⁻¹. These values are independent of the target size. Extrapolation of the measured velocity dependence of the volume filling factor implies that higher collision velocities will not lead to more compact aggregates. Therefore, ϕ = 0.32 marks a degree of compaction suitable for describing structures forming at v > 6 m s⁻¹. At small collision velocities below 1 m s⁻¹, highly porous structures with ϕ ≈ 0.10 will form. For intermediate collision velocities porosities vary. Depending on the disk model and resulting relative velocities, objects in protoplanetary disks up to decimeters in size might evolve from highly porous (ϕ ≈ 0.10) to compact (ϕ = 0.32) with a more complex intermediate size range of varying porosity.

We present early- and late-time photometric and spectroscopic observations of supernova (SN) 2009hd in the nearby spiral galaxy NGC 3627 (M66). This SN is one of the closest to us in recent years and provides an uncommon opportunity to observe and study the nature of SNe. However, the object was heavily obscured by dust, rendering it unusually faint in the optical given its proximity. We find that the observed properties of SN 2009hd support its classification as a possible Type II-Linear SN (SN II-L), a relatively rare subclass of core-collapse SNe. High-precision relative astrometry has been employed to attempt to identify an SN progenitor candidate, based on a pixel-by-pixel comparison between Hubble Space Telescope (HST) F555W and F814W images of the SN site prior to explosion and at late times. A progenitor candidate is identified in the F814W images only; this object is undetected in F555W. Significant uncertainty exists in the astrometry, such that we cannot definitively identify this object as the SN progenitor. Via insertion of artificial stars into the pre-SN HST images, we are able to constrain the progenitor's properties to those of a possible supergiant, with intrinsic absolute magnitude M⁰_F555W ≳ −7.6 mag and intrinsic color (V − I)⁰ ≳ 0.99 mag. The magnitude and color limits are consistent with a luminous red supergiant (RSG); however, they also allow for the possibility that the star could have been more yellow than red. From a comparison with theoretical massive-star evolutionary tracks which include rotation and pulsationally enhanced mass loss, we can place a conservative upper limit on the initial mass for the progenitor of M_ini ≲ 20 M_☉. If the actual mass of the progenitor is near the upper range allowed by our derived mass limit, then it would be consistent with that for the identified progenitors of the SN II-L 2009kr and the high-luminosity SN II-Plateau (II-P) 2008cn. The progenitors of these three SNe may possibly bridge the gap between lower-mass RSGs that explode as SNe II-P and luminous blue variables, or more extreme RSGs, from which the more exotic SNe II-narrow may arise. Very late time imaging of the SN 2009hd site may provide us with more clues regarding the true nature of its progenitor.

We present Spitzer Multiband Imaging Photometer (MIPS) spectral energy distribution (SED) and Infrared Spectrograph (IRS) observations of 14 Galactic supernova remnants (SNRs) previously identified in the GLIMPSE survey. We find evidence for SNR/molecular cloud interaction through detection of [O i] emission, ionic lines, and emission from molecular hydrogen. Through blackbody fitting of the MIPS SEDs we find the large grains to be warm, 29–66 K. The dust emission is modeled using the DUSTEM code and a three-component dust model composed of populations of big grains (BGs), very small grains (VSGs), and polycyclic aromatic hydrocarbons. We find the dust to be moderately heated, typically by 30–100 times the interstellar radiation field. The source of the radiation is likely hydrogen recombination, where the excitation of hydrogen occurred in the shock front. The ratio of VSGs to BGs is found for most of the molecular interacting SNRs to be higher than that found in the plane of the Milky Way, typically by a factor of 2–3. We suggest that dust shattering is responsible for the relative overabundance of small grains, in agreement with the prediction from dust destruction models. However, two of the SNRs are best fitted with a very low abundance of carbon grains to silicate grains and with a very high radiation field. A likely reason for the low abundance of small carbon grains is sputtering. We find evidence for silicate emission at 20 μm in their SEDs, indicating that they are young SNRs based on the strong radiation field necessary to reproduce the observed SEDs.

We study local radiation magnetohydrodynamic instabilities in static, optically thick, vertically stratified media with constant flux mean opacity. We include the effects of vertical gradients in a horizontal background magnetic field. Assuming rapid radiative diffusion, we use the zero gas pressure limit as an entry point for investigating the coupling between the photon bubble instability and the Parker instability. Apart from factors that depend on wavenumber orientation, the Parker instability exists for wavelengths longer than a characteristic wavelength λ_tran, while photon bubbles exist for wavelengths shorter than λ_tran. The growth rate in the Parker regime is independent of the orientation of the horizontal component of the wavenumber when radiative diffusion is rapid, but the range of Parker-like wavenumbers is extended if there exists strong horizontal shear between field lines (i.e., horizontal wavenumber perpendicular to the magnetic field). Finite gas pressure introduces an additional short-wavelength limit to the Parker-like behavior, and also limits the growth rate of the photon bubble instability to a constant value at short wavelengths. We also consider the effects of differential rotation with accretion disk applications in mind. Our results may explain why photon bubbles have not yet been observed in recent stratified shearing box accretion disk simulations. Photon bubbles may physically exist in simulations with high radiation to gas pressure ratios, but higher spatial resolution will be needed to resolve the asymptotically growing unstable wavelengths.

A rotating, two-dimensional stellar model is evolved to match the approximate conditions of α Oph. Both axisymmetric and nonaxisymmetric oscillation frequencies are computed for two-dimensional rotating models which approximate the properties of α Oph. These computed frequencies are compared to the observed frequencies. Oscillation calculations are made assuming the eigenfunction can be fitted with six Legendre polynomials, but comparison calculations with eight Legendre polynomials show the frequencies agree to within about 0.26% on average. The surface horizontal shape of the eigenfunctions for the two sets of assumed number of Legendre polynomials agrees less well, but all calculations show significant departures from that of a single Legendre polynomial. It is still possible to determine the large separation, although the small separation is more complicated to estimate. With the addition of the nonaxisymmetric modes with |m| ⩽ 4, the frequency space becomes sufficiently dense that it is difficult to comment on the adequacy of the fit of the computed to the observed frequencies. While the nonaxisymmetric frequency mode splitting is no longer uniform, the frequency difference between the frequencies for positive and negative values of the same m remains 2m times the rotation rate.

Stars form in dense cores of magnetized molecular clouds. If the magnetic flux threading the cores is dragged into the stars, the stellar field would be orders of magnitude stronger than observed. This well-known “magnetic flux problem” demands that most of the core magnetic flux be decoupled from the matter that enters the star. We carry out the first exploration of what happens to the decoupled magnetic flux in three dimensions, using a magnetohydrodynamic (MHD) version of the ENZO adaptive mesh refinement code. The field–matter decoupling is achieved through a sink particle treatment, which is needed to follow the protostellar accretion phase of star formation. We find that the accumulation of the decoupled flux near the accreting protostar leads to a magnetic pressure buildup. The high pressure is released anisotropically along the path of least resistance. It drives a low-density expanding region in which the decoupled magnetic flux is expelled. This decoupling-enabled magnetic structure has never been seen before in three-dimensional MHD simulations of star formation. It generates a strong asymmetry in the protostellar accretion flow, potentially giving a kick to the star. In the presence of an initial core rotation, the structure presents an obstacle to the formation of a rotationally supported disk, in addition to magnetic braking, by acting as a rigid magnetic wall that prevents the rotating gas from completing a full orbit around the central object. We conclude that the decoupled magnetic flux from the stellar matter can strongly affect the protostellar collapse dynamics.

We have used the Institut de Radioastronomie Millimétrique (IRAM) Plateau de Bure Interferometer and the Expanded Very Large Array to obtain a high-resolution map of the CO(6–5) and CO(1–0) emission in the lensed, star-forming galaxy SMM J2135−0102 at z = 2.32. The kinematics of the gas are well described by a model of a rotationally supported disk with an inclination-corrected rotation speed, v_rot = 320 ± 25 km s⁻¹, a ratio of rotational-to-dispersion support of v/σ = 3.5 ± 0.2, and a dynamical mass of (6.0 ± 0.5) × 10¹⁰ M_☉ within a radius of 2.5 kpc. The disk has a Toomre parameter, Q = 0.50 ± 0.15, suggesting that the gas will rapidly fragment into massive clumps on scales of L_J ∼ 400 pc. We identify star-forming regions on these scales and show that they are ∼10 × denser than those in quiescent environments in local galaxies, and significantly offset from the local molecular cloud scaling relations (Larson's relations). The large offset compared to local molecular cloud line-width–size scaling relations implies that supersonic turbulence should remain dominant on scales ∼100× smaller than in the kinematically quiescent interstellar medium (ISM) of the Milky Way, while the molecular gas in SMM J2135 is expected to be ∼50× denser than that in the Milky Way on all scales. This is most likely due to the high external hydrostatic pressure we measure for the ISM, P_tot/k_B ∼ (2 ± 1) × 10⁷ K cm⁻³. In such highly turbulent ISM, the subsonic regions of gravitational collapse (and star formation) will be characterized by much higher critical densities, n_crit > = 10⁸ cm⁻³, a factor ≳1000× more than the quiescent ISM of the Milky Way.

We demonstrate a signal-processing concept for imaging the sky at millisecond rates with radio interferometers. The “Pocket Correlator” (PoCo) correlates the signals from multiple elements of a radio interferometer fast enough to image brief, dispersed pulses. By the nature of interferometry, a millisecond correlator functions like a large, single-dish telescope, but with improved survey speed, spatial localization, calibration, and interference rejection. To test the concept, we installed PoCo at the Allen Telescope Array (ATA) to search for dispersed pulses from the Crab pulsar, B0329+54, and M31 using total-power, visibility-based, and image-plane techniques. In 1.7 hr of observing, PoCo detected 191 giant pulses from the Crab pulsar brighter than a typical 5σ sensitivity limit of 60 Jy over pulse widths of 3 ms. Roughly 40% of pulses from pulsar B0329+54 were detected by using novel visibility-based techniques. Observations of M31 constrain the rate of pulses brighter than 190 Jy in a three-degree region surrounding the galaxy to <4.3 hr⁻¹. We calculate the computational demand of various visibility-based pulse search algorithms and demonstrate how compute clusters can help meet this demand. Larger implementations of the fast imaging concept will conduct blind searches for millisecond pulses in our Galaxy and beyond, providing a valuable probe of the interstellar/intergalactic media, discovering new kinds of radio transients, and localizing them to constrain models of their origin.

We investigate the formation of the first massive black holes (MBHs) in high redshift galaxies, with the goal of providing insights to which galaxies do or do not host MBHs. We adopt a novel approach to forming seed black holes in galaxy halos in cosmological SPH+N-body simulations. The formation of MBH seeds is dictated directly by the local gas density, temperature, and metallicity, and motivated by physical models of MBH formation. We explore seed black hole populations as a function of halo mass and redshift, and examine how varying the efficiency of MBH seed formation affects the relationship between black holes and their hosts. Seed black holes tend to form in halos with mass between 10⁷ and 10⁹M_☉, and the formation rate is suppressed around z = 5 due to the diffusion of metals throughout the intergalactic medium. We find that the time of MBH formation and the occupation fraction of black holes are a function of the host halo mass. By z = 5, halos with mass M_halo > 3 × 10⁹M_☉ host MBHs regardless of the efficiency of seed formation, while the occupation fraction for smaller halos increases with black hole formation efficiency. Our simulations explain why MBHs are found in some bulgeless and dwarf galaxies, but we also predict that their occurrence becomes rarer and rarer in low-mass systems.

The Transition Radiation Array for Cosmic Energetic Radiation (TRACER) cosmic-ray detector, first flown on long-duration balloon (LDB) in 2003 for observations of the major primary cosmic-ray nuclei from oxygen (Z = 8) to iron (Z = 26), has been upgraded to also measure the energies of the lighter nuclei, including the secondary species boron (Z = 5). The instrument was used in another LDB flight in 2006. The properties and performance of the modified detector system are described, and the analysis of the data from the 2006 flight is discussed. The energy spectra of the primary nuclei carbon (Z = 6), oxygen, and iron over the range from 1 GeV amu⁻¹ to 2 TeV amu⁻¹ are reported. The data for oxygen and iron are found to be in good agreement with the results of the previous TRACER flight. The measurement of the energy spectrum of boron also extends into the TeV amu⁻¹ region. The relative abundances of the primary nuclei, such as carbon, oxygen, and iron, above ∼10 GeV amu⁻¹ are independent of energy, while the boron abundance, i.e., the B/C abundance ratio, decreases with energy as expected. However, there is an indication that the previously reported E^−0.6 dependence of the B/C ratio does not continue to the highest energies.

We perform high-resolution ray-tracing simulations to investigate probability distribution functions (PDFs) of lensing convergence, shear, and magnification on distant sources up to the redshift of z_s = 20. We pay particular attention to the shot noise effect in N-body simulations by explicitly showing how it affects the variance of the convergence. We show that the convergence and magnification PDFs are closely related to each other via the approximate relation μ = (1 − κ)⁻², which can reproduce the behavior of PDFs surprisingly well up to the high magnification tail. The mean convergence measured in the source plane is found to be systematically negative, rather than zero as often assumed, and is correlated with the convergence variance. We provide simple analytical formulae for the PDFs, which reproduce simulated PDFs reasonably well for a wide range of redshifts and smoothing sizes. As explicit applications of our ray-tracing simulations, we examine the strong-lensing probability and the magnification effects on the luminosity functions of distant galaxies and quasars.

It has long been regarded as difficult if not impossible for a cosmological model to account simultaneously for the galaxy luminosity, mass, and velocity distributions. We revisit this issue using a modern compilation of observational data along with the best available large-scale cosmological simulation of dark matter (DM). We find that the standard cosmological model, used in conjunction with halo abundance matching (HAM) and simple dynamical corrections, fits—at least on average—all basic statistics of galaxies with circular velocities V_circ > 80 km s⁻¹ calculated at a radius of ∼10 kpc. Our primary observational constraint is the luminosity–velocity (LV) relation—which generalizes the Tully–Fisher and Faber–Jackson relations in allowing all types of galaxies to be included, and provides a fundamental benchmark to be reproduced by any theory of galaxy formation. We have compiled data for a variety of galaxies ranging from dwarf irregulars to giant ellipticals. The data present a clear monotonic LV relation from ∼50 km s⁻¹ to ∼500 km s⁻¹, with a bend below ∼80 km s⁻¹ and a systematic offset between late- and early-type galaxies. For comparison to theory, we employ our new ΛCDM “Bolshoi” simulation of DM, which has unprecedented mass and force resolution over a large cosmological volume, while using an up-to-date set of cosmological parameters. We use HAM to assign rank-ordered galaxy luminosities to the DM halos, a procedure that automatically fits the empirical luminosity function and provides a predicted LV relation that can be checked against observations. The adiabatic contraction of DM halos in response to the infall of the baryons is included as an optional model ingredient. The resulting predictions for the LV relation are in excellent agreement with the available data on both early-type and late-type galaxies for the luminosity range from M_r = −14 to M_r = −22. We also compare our predictions for the “cold” baryon mass (i.e., stars and cold gas) of galaxies as a function of circular velocity with the available observations, again finding a very good agreement. The predicted circular velocity function (VF) is also in agreement with the galaxy VF from 80 to 400 km s⁻¹, using the HIPASS survey for late-type galaxies and Sloan Digital Sky Survey (SDSS) for early-type galaxies. However, in accord with other recent results, we find that the DM halos with V_circ < 80 km s⁻¹ are much more abundant than observed galaxies with the same V_circ. Finally, we find that the two-point correlation function of bright galaxies in our model matches very well the results from the final data release of the SDSS, especially when a small amount of scatter is included in the HAM prescription.

The accreting millisecond pulsar XTE J1807-294 is studied through a pulse-shape modeling analysis. The model includes blackbody and Comptonized emission from the one visible hot spot and makes use of the Oblate Schwarzschild approximation for ray-tracing. We include a scattered light contribution, which accounts for flux scattered off an equatorial accretion disk to the observer including time delays in the scattered light. We give limits to mass and radius for XTE J1807-294 and compare these to limits determined for SAX J1808-3658 and XTE J1814-334 previously determined using similar methods. The resulting allowed region for mass–radius curves is small but consistent with a mass–radius relation with nearly constant radius (∼12 km) for masses between 1 and 2.5 solar masses.

We present a detailed and unique mass budget for the high surface brightness galaxy UGC 463, showing it is dominated by dark matter (DM) at radii beyond one scale length (h_R) and has a baryonic-to-DM mass ratio of approximately 1:3 within 4.2h_R. Assuming a constant scale height (h_z; calculated via an empirical oblateness relation), we calculate dynamical disk mass surface densities from stellar kinematics, which provide vertical velocity dispersions after correcting for the shape of the stellar velocity ellipsoid (measured to have σ_θ/σ_R = 1.04 ± 0.22 and σ_z/σ_R = 0.48 ± 0.09). We isolate the stellar mass surface density by accounting for all gas mass components and find an average K-band mass-to-light ratio of ; Zibetti et al. and Bell et al. predict, respectively, 0.56 and 3.6 times our dynamical value based on stellar-population-synthesis modeling. The baryonic matter is submaximal by a factor of ∼3 in mass and the baryonic-to-total circular-speed ratio is 0.61^+0.07_−0.09(ran)^+0.12_−0.18(sys) at 2.2h_R; however, the disk is globally stable with a multi-component stability that decreases asymptotically with radius to Q ∼ 2. We directly calculate the circular speed of the DM halo by subtracting the baryonic contribution to the total circular speed; the result is equally well described by either a Navarro–Frenk–White halo or a pseudo-isothermal sphere. The volume density is dominated by DM at heights of |z| ≳ 1.6h_z for radii of R ≳ h_R. As is shown in follow-up papers, UGC 463 is just one example among nearly all galaxies we have observed that contradict the hypothesis that high surface brightness spiral galaxies have maximal disks.

We analyze with our entropy-based Supermodel a library of 12 galaxy clusters featuring extended X-ray observations of their intracluster plasma (ICP). The few intrinsic parameters of the model—basically, the central level and the outer slope of the entropy profile—enable us to uniformly derive not only robust snapshots of the ICP thermal state, but also the “concentration” parameter marking the age of the host dark matter (DM) halo. We test these profiles for consistency with numerical simulations and observations. We find the central and the outer entropy correlate, so that these clusters split into two main classes defined on the basis of low (LE) or high entropy (HE) conditions prevailing throughout the ICP. We also find inverse correlations between the central/outer entropy and the halo concentration. We interpret these in terms of mapping the ICP progress on timescales around 5 Gyr toward higher concentrations, under the drive of the DM halo development. The progress proceeds from HE clusters to LE clusters, toward states of deeper entropy erosion by radiative cooling in the inner regions and of decreasing outer entropy production as the accretion peters out. We propose these radial and time features constitute a cluster Grand Design that we use here to derive a number of predictions. For HE clusters we predict sustained outer temperature profiles. For LEs we expect the outer entropy ramp to bend over; hence the temperature declines before steepening at low z; this feature goes together with an increasing turbulent support, a condition that can be directly probed with the Sunyaev–Zel'dovich effect. We finally discuss the looming out of two intermediate subsets: a wiggled at low z that features central temperature profiles retaining imprints of entropy discharged by active galactic nuclei or deep mergers and high-z LEs where the cosmogony/cosmology had little time to enforce a sharp outer entropy bending.

We introduce a method for measuring the slopes of mass profiles within dwarf spheroidal (dSph) galaxies directly from stellar spectroscopic data and without adopting a dark matter halo model. Our method combines two recent results: (1) spherically symmetric, equilibrium Jeans models imply that the product of half-light radius and (squared) stellar velocity dispersion provides an estimate of the mass enclosed within the half-light radius of a dSph stellar component, and (2) some dSphs have chemodynamically distinct stellar subcomponents that independently trace the same gravitational potential. We devise a statistical method that uses measurements of stellar positions, velocities, and spectral indices to distinguish two dSph stellar subcomponents and to estimate their individual half-light radii and velocity dispersions. For a dSph with two detected stellar subcomponents, we obtain estimates of masses enclosed at two discrete points in the same mass profile, immediately defining a slope. Applied to published spectroscopic data, our method distinguishes stellar subcomponents in the Fornax and Sculptor dSphs, for which we measure slopes Γ ≡ Δlog M/Δlog r = 2.61^+0.43_−0.37 and Γ = 2.95^+0.51_−0.39, respectively. These values are consistent with “cores” of constant density within the central few hundred parsecs of each galaxy and rule out “cuspy” Navarro–Frenk–White (NFW) profiles (dlog M/dlog r ⩽ 2 at all radii) with a significance ≳ 96% and ≳ 99%, respectively. Tests with synthetic data indicate that our method tends systematically to overestimate the mass of the inner stellar subcomponent to a greater degree than that of the outer stellar subcomponent, and therefore to underestimate the slope Γ (implying that the stated NFW exclusion levels are conservative).

We report determinations of the molybdenum abundances in five mildly to extremely metal-poor turnoff stars using five Mo ii lines near 2000 Å. In two of the stars, the abundance of molybdenum is found to be extremely enhanced, as high or higher than the neighboring even-Z elements ruthenium and zirconium. Of the several nucleosynthesis scenarios envisioned for the production of nuclei in this mass range in the oldest stars, a high-entropy wind acting in a core-collapse supernova seems uniquely capable of the twin aspects of a high molybdenum overproduction confined to a narrow mass range. Whatever the details of the nucleosynthesis mechanism, however, this unusual excess suggests that very few individual nucleosynthesis events were responsible for the synthesis of the light trans-Fe heavy elements in these cases, an unexpected result given that both are only moderately metal-poor.

We examine the ability to test the black hole no-hair theorem at the 10% level in this decade using the binary black hole in OJ287. In the test we constrain the value of the dimensionless parameter q that relates the scaled quadrupole moment and spin of the primary black hole: q₂ = −q χ². At the present we can say that q = 1 ± 0.3 (1σ), in agreement with general relativity and the no-hair theorems. We demonstrate that this result can be improved if more observational data are found in historical plate archives for the 1959 and 1971 outbursts. We also show that the predicted 2015 and 2019 outbursts will be crucial in improving the accuracy of the test. Space-based photometry is required in 2019 July due the proximity of OJ287 to the Sun at the time of the outburst. The best situation would be to carry out the photometry far from the Earth, from quite a different vantage point, in order to avoid the influence of the nearby Sun. We have considered in particular the STEREO space mission, which would be ideal if it has a continuation in 2019, or the Long Range Reconnaissance Imager on board the New Horizons mission to Pluto.

This paper is the third in a series in which we present deep Chandra ACIS-S imaging spectroscopy of the Seyfert 1 galaxy NGC 4151, devoted to study its complex circumnuclear X-ray emission. Emission features in the soft X-ray spectrum of the bright extended emission (L_{0.3–2 keV} ∼ 10⁴⁰ erg s⁻¹) at r > 130 pc (2″) are consistent with blended brighter O vii, O viii, and Ne ix lines seen in the Chandra HETGS and XMM-Newton RGS spectra below 2 keV. We construct emission line images of these features and find good morphological correlations with the narrow-line region clouds mapped in [O iii] λ5007. Self-consistent photoionization models provide good descriptions of the spectra of the large-scale emission, as well as resolved structures, supporting the dominant role of nuclear photoionization, although displacement of optical and X-ray features implies a more complex medium. Collisionally ionized emission is estimated to be ≲12% of the extended emission. Presence of both low- and high-ionization spectral components and extended emission in the X-ray image perpendicular to the bicone indicates leakage of nuclear ionization, likely filtered through warm absorbers, instead of being blocked by a continuous obscuring torus. The ratios of [O iii]/soft X-ray flux are approximately constant (∼15) for the 1.5 kpc radius spanned by these measurements, indicating similar relative contributions from the low- and high-ionization gas phases at different radial distances from the nucleus. If the [O iii] and X-ray emission arise from a single photoionized medium, this further implies an outflow with a wind-like density profile. Using spatially resolved X-ray features, we estimate that the mass outflow rate in NGC 4151 is ∼2 M_☉ yr⁻¹ at 130 pc and the kinematic power of the ionized outflow is 1.7 × 10⁴¹ erg s⁻¹, approximately 0.3% of the bolometric luminosity of the active nucleus in NGC 4151.

Exploiting the Herschel Astrophysical Terahertz Large Area Survey Science Demonstration Phase survey data, we have determined the luminosity functions (LFs) at rest-frame wavelengths of 100 and 250 μm and at several redshifts z ≳ 1, for bright submillimeter galaxies with star formation rates (SFRs)  ≳  100 M_☉ yr⁻¹. We find that the evolution of the comoving LF is strong up to z ≈ 2.5, and slows down at higher redshifts. From the LFs and the information on halo masses inferred from clustering analysis, we derived an average relation between SFR and halo mass (and its scatter). We also infer that the timescale of the main episode of dust-enshrouded star formation in massive halos (M_H ≳ 3 × 10¹² M_☉) amounts to ∼7 × 10⁸ yr. Given the SFRs, which are in the range of 10²–10³ M_☉ yr⁻¹, this timescale implies final stellar masses of the order of 10¹¹–10¹² M_☉. The corresponding stellar mass function matches the observed mass function of passively evolving galaxies at z ≳ 1. The comparison of the statistics for submillimeter and UV-selected galaxies suggests that the dust-free, UV bright phase is ≳ 10² times shorter than the submillimeter bright phase, implying that the dust must form soon after the onset of star formation. Using a single reference spectral energy distribution (SED; the one of the z ≈ 2.3 galaxy SMM J2135-0102), our simple physical model is able to reproduce not only the LFs at different redshifts >1 but also the counts at wavelengths ranging from 250 μm to ≈1 mm. Owing to the steepness of the counts and their relatively broad frequency range, this result suggests that the dispersion of submillimeter SEDs of z > 1 galaxies around the reference one is rather small.

A subset of microquasars exhibits high peculiar velocity with respect to the local standard of rest due to the kicks they receive when being born in supernovae. The interaction between the radio plasma released by microquasar jets from such high-velocity binaries with the interstellar medium must lead to the production of trails and bow shocks similar to what is observed in narrow-angle tailed radio galaxies and pulsar wind nebulae. We present a set of numerical simulations of this interaction that illuminate the long-term dynamical evolution and the observational properties of these microquasar bow-shock nebulae and trails. We find that this interaction always produces a structure that consists of a bow shock, a trailing neck, and an expanding bubble. Using our simulations to model emission, we predict that the shock surrounding the bubble and the neck should be visible in H_α emission, the interior of the bubble should be visible in synchrotron radio emission, and only the bow shock is likely to be detectable in X-ray emission. We construct an analytic model for the evolution of the neck and bubble shape and compare this model with observations of the X-ray binary SAX J1712.6-3739.

We present a joint crossed molecular beam and kinetics investigation combined with electronic structure and statistical calculations on the reaction of the ground-state cyano radical, CN(X²Σ⁺), with the 1,3-butadiene molecule, H₂CCHCHCH₂(X¹A_g), and its partially deuterated counterparts, H₂CCDCDCH₂(X¹A_g) and D₂CCHCHCD₂(X¹A_g). The crossed beam studies indicate that the reaction proceeds via a long-lived C₅H₆N complex, yielding C₅H₅N isomer(s) plus atomic hydrogen under single collision conditions as the nascent product(s). Experiments with the partially deuterated 1,3-butadienes indicate that the atomic hydrogen loss originates from one of the terminal carbon atoms of 1,3-butadiene. A combination of the experimental data with electronic structure calculations suggests that the thermodynamically less favorable 1-cyano-1,3-butadiene isomer represents the dominant reaction product; possible minor contributions of less than a few percent from the aromatic pyridine molecule might be feasible. Low-temperature kinetics studies demonstrate that the overall reaction is very fast from room temperature down to 23 K with rate coefficients close to the gas kinetic limit. This finding, combined with theoretical calculations, indicates that the reaction proceeds on an entrance barrier-less potential energy surface (PES). This combined experimental and theoretical approach represents an important step toward a systematic understanding of the formation of complex, nitrogen-bearing molecules—here on the C₅H₆N PES—in low-temperature extraterrestrial environments. These results are compared to the reaction dynamics of D1-ethynyl radicals (C₂D; X²Σ⁺) with 1,3-butadiene accessing the isoelectronic C₆H₇ surface as tackled earlier in our laboratories.

We investigate the Fermi Large Area Telescope γ-ray and 15 GHz Very Long Baseline Array radio properties of a joint γ-ray and radio-selected sample of active galactic nuclei (AGNs) obtained during the first 11 months of the Fermi mission (2008 August 4–2009 July 5). Our sample contains the brightest 173 AGNs in these bands above declination −30° during this period, and thus probes the full range of γ-ray loudness (γ-ray to radio band luminosity ratio) in the bright blazar population. The latter quantity spans at least 4 orders of magnitude, reflecting a wide range of spectral energy distribution (SED) parameters in the bright blazar population. The BL Lac objects, however, display a linear correlation of increasing γ-ray loudness with synchrotron SED peak frequency, suggesting a universal SED shape for objects of this class. The synchrotron self-Compton model is favored for the γ-ray emission in these BL Lac objects over external seed photon models, since the latter predict a dependence of Compton dominance on Doppler factor that would destroy any observed synchrotron SED-peak–γ-ray-loudness correlation. The high-synchrotron peaked (HSP) BL Lac objects are distinguished by lower than average radio core brightness temperatures, and none display large radio modulation indices or high linear core polarization levels. No equivalent trends are seen for the flat-spectrum radio quasars (FSRQs) in our sample. Given the association of such properties with relativistic beaming, we suggest that the HSP BL Lac objects have generally lower Doppler factors than the lower-synchrotron peaked BL Lac objects or FSRQs in our sample.

Methanol (CH₃OH) is thought to be an important link in the chain of chemical evolution that leads from simple diatomic interstellar molecules to complex organic species in protoplanetary disks that may be delivered to the surfaces of Earthlike planets. Previous research has shown that CH₃OH forms in the interstellar medium predominantly on the surfaces of dust grains. To enhance our understanding of the conditions that lead to its efficient production, we assemble a homogenized catalog of published detections and limiting values in interstellar and preplanetary ices for both CH₃OH and the other commonly observed C- and O-bearing species, H₂O, CO, and CO₂. We use this catalog to investigate the abundance of ice-phase CH₃OH in environments ranging from dense molecular clouds to circumstellar envelopes around newly born stars of low and high mass. Results show that CH₃OH production arises during the CO freezeout phase of ice-mantle growth in the clouds, after an ice layer rich in H₂O and CO₂ is already in place on the dust, in agreement with current astrochemical models. The abundance of solid-phase CH₃OH in this environment is sufficient to account for observed gas-phase abundances when the ices are subsequently desorbed in the vicinity of embedded stars. CH₃OH concentrations in the ices toward embedded stars show order-of-magnitude object-to-object variations, even in a sample restricted to stars of low mass associated with ices lacking evidence of thermal processing. We hypothesize that the efficiency of CH₃OH production in dense cores and protostellar envelopes is mediated by the degree of prior CO depletion.

The white-light corona (WLC) during the total solar eclipse of 2009 July 22 was observed by several teams in the Moon's shadow stretching from India and China across the Pacific Ocean with its many isolated islands. We present a comparison of the WLC as observed by eclipse teams located in China (Shanghai region) and on the Enewetak Atoll in the Marshall Islands, with observations taken 112 minutes apart, combined with near-simultaneous space observations. The eclipse was observed at the beginning of solar cycle 24, during a deep solar minimum (officially estimated as 2008 December according to the smoothed sunspot number, but very extended). The solar corona shows several different types of features (coronal holes, polar rays, helmet streamers, faint loops, voids, etc.), though it was extremely sparse in streamers as shown from Large-Angle Spectroscopic Coronagraph data. No large-scale dynamical phenomena were seen when comparing the observations from the two sites, confirming that the corona was quiescent. We measure a Ludendorff flattening coefficient of 0.238, typical of solar minimum.

We have investigated the degree to which turbulence in the Very Local Interstellar Clouds resembles the highly studied turbulence in the solar corona and the solar wind, particularly the high-speed solar wind. The turbulence diagnostics for the Local Clouds are the absorption line widths measured along 32 lines of sight to nearby stars, yielding measurements for 53 absorption components. We have tested whether the Local Cloud turbulence has the following properties of turbulence in the solar corona or the solar wind: (1) velocity fluctuations mainly perpendicular to the average magnetic field, (2) a temperature anisotropy in the sense that the perpendicular temperature is larger than the parallel temperature (or at least enhanced relative to expectation), and (3) an ion temperature which is dependent on the ion Larmor radius, in the sense that more massive ions have higher temperatures. Our analysis of the data does not show compelling evidence for any of these properties in Local Cloud turbulence, indicating possible differences with the aforementioned heliospheric plasmas. In the case of anisotropy of velocity fluctuations, although the expected observational signature is not seen, we cannot exclude the possibility of relatively high degrees of anisotropy (anisotropy parameter ∼ 0.50–0.70), if some other process in the Local Clouds is causing variations in the turbulent line width from one line of sight to another. We briefly consider possible reasons for differences between heliospheric turbulence and that in the Local Clouds. The apparent absence of anisotropy of the velocity fluctuations and ion temperature might be due to randomization of the interstellar magnetic field on spatial scales ∼10 pc, but this would not explain the absence of ion mass dependence in the ion temperature. A likely explanation for the absence of temperature anisotropy and mass-proportional temperature in the Local Clouds, and the presence of these effects in the corona and high-speed solar wind, is the greater collisionality, due to ion–neutral collisions, of the partially ionized Local Cloud plasma.

It has long been thought that the pulsed X-ray properties of rotation-powered pulsars are stable on long timescales. However, long-term, systematic studies of individual sources have been lacking. Furthermore, dramatic X-ray variability has now been observed from two pulsars having inferred sub-critical dipole magnetic fields. Here we present an analysis of the long-term pulsed X-ray properties of the young, energetic pulsar PSR B1509−58 using data from the Rossi X-ray Timing Explorer. We measured the 2–50 keV pulsed flux for 14.7 yr of X-ray observations and found that it is consistent with being constant on all relevant timescales, and place a 3σ upper limit on day-to-week variability of <28%. In addition, we searched for magnetar-like X-ray bursts in all observations and found none, which we use to constrain the measurable burst rate to less than one per 750 ks of observations. We also searched for variability in the pulse profile and found that it is consistent with being stable on timescales of days to decades. This supports the hypothesis that X-ray properties of rotation-powered X-ray pulsars can be stable on decade-long timescales. In addition, we extend the existing timing solution by 7.1 yr to a total of 28.4 yr and report updated values of the braking index, n = 2.832 ± 0.003, and the second braking index, m = 17.6 ± 1.9.

We examine the tidal disruption event (TDE) scenario to explain Sw 1644+57, a powerful and persistent X-ray source which suddenly became active as GRB 110328A. The precise localization at the center of a z = 0.35 galaxy argues for activity of the central engine as the underlying cause. We look at the suggestion by Bloom et al. of the possibility of a TDE. We argue that Sw 1644+57 cannot be explained by the traditional TDE model in which the periastron distance is close to the tidal disruption radius—three independent lines of argument indicate the orbit must be deeply plunging or else the powerful jet we are observing could not be produced. These arguments stem from (1) comparing the early X-ray light curve to the expected theoretical fallback rate, (2) looking at the time of transition to disk-dominated decay, and (3) considering the TDE rate. Due to the extreme excess in the tidal force above that which would be required minimally to disrupt the star in a deeply plunging orbit at periastron, we suggest this scenario might be referred to more descriptively as a tidal obliteration event (TOE) rather than a TDE.

We present the mass function of supermassive black holes (SMBHs) over the redshift range z = 0–2, using the latest deep luminosity and mass functions of field galaxies to constrain the masses of their spheroids, which we relate to SMBH mass through the empirical correlation between SMBH and spheroid mass (the M_•–M_sph relation). In addition to luminosity fading of the stellar content of the spheroids, we carefully consider the variation of the bulge-to-total luminosity ratio of the galaxy populations and the M_•/M_sph ratio, which, according to numerous recent studies, evolves rapidly with redshift. The SMBH mass functions derived from the galaxy luminosity and mass functions show very good agreement, both in shape and in normalization. The resultant SMBH mass function and integrated mass density for the local epoch (z ≈ 0) match well those derived independently by other studies. Consistent with other evidence for cosmic downsizing, the upper end of the mass function remains roughly constant since z ≈ 2, while the space density of lower mass black holes undergoes strong evolution. We carefully assess the impact of various sources of uncertainties on our calculations. A companion paper uses the mass function derived in this work to determine the radiative efficiency of black hole accretion and constraints that can be imposed on the cosmological evolution of black hole spin.

We study the generation of large-scale vortices in rotating turbulent convection by means of Cartesian direct numerical simulations. We find that for sufficiently rapid rotation, cyclonic structures on a scale large in comparison to that of the convective eddies emerge, provided that the fluid Reynolds number exceeds a critical value. For slower rotation, cool cyclonic vortices are preferred, whereas for rapid rotation, warm anti-cyclonic vortices are favored. In some runs in the intermediate regime both types of cyclones coexist for thousands of convective turnover times. The temperature contrast between the vortices and the surrounding atmosphere is of the order of 5%. We relate the simulation results to observations of rapidly rotating late-type stars that are known to exhibit large high-latitude spots from Doppler imaging. In many cases, cool spots are accompanied with spotted regions with temperatures higher than the average. In this paper, we investigate a scenario according to which of the spots observed in the temperature maps could have a non-magnetic origin due to large-scale vortices in the convection zones of the stars.

The transiting exoplanet WASP-18b was discovered in 2008 by the Wide Angle Search for Planets project. The Spitzer Exoplanet Target of Opportunity Program observed secondary eclipses of WASP-18b using Spitzer's Infrared Array Camera in the 3.6 μm and 5.8 μm bands on 2008 December 20, and in the 4.5 μm and 8.0 μm bands on 2008 December 24. We report eclipse depths of 0.30% ± 0.02%, 0.39% ± 0.02%, 0.37% ± 0.03%, 0.41% ± 0.02%, and brightness temperatures of 3100 ± 90, 3310 ± 130, 3080 ± 140, and 3120 ± 110 K in order of increasing wavelength. WASP-18b is one of the hottest planets yet discovered—as hot as an M-class star. The planet's pressure–temperature profile most likely features a thermal inversion. The observations also require WASP-18b to have near-zero albedo and almost no redistribution of energy from the day side to the night side of the planet.

The problem of a non-steady planar radiation-mediated shock (RMS) breaking out from a surface with a power-law density profile, ρ∝xⁿ, is numerically solved in the approximation of diffusion with constant opacity. For an appropriate choice of time, length, and energy scales, determined by the breakout opacity, velocity, and density, the solution is universal, i.e., depends only on the density power-law index n. The resulting luminosity depends weakly on the value of n. An approximate analytic solution, based on the self-similar hydrodynamic solutions and on the steady RMS solutions, is constructed and shown to agree with the numerical solutions as long as the shock is far from the surface, τ ≫ c/v_sh. Approximate analytic expressions, calibrated based on the exact solutions, are provided, which describe the escaping luminosity as a function of time. These results can be used to calculate the bolometric properties of the bursts of radiation produced during supernova shock breakouts. For completeness, we also use the exact breakout solutions to provide an analytic approximation for the maximum surface temperature for fast (v_sh ≳ 0.1) non-thermal breakouts and show that it is a few times smaller than inferred based on steady state RMS solutions.

We present an empirical s-process abundance distribution derived with explicit knowledge of the r-process component in the low-metallicity globular cluster M22. We have obtained high-resolution, high signal-to-noise spectra for six red giants in M22 using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan-Clay Telescope at Las Campanas Observatory. In each star we derive abundances for 44 species of 40 elements, including 24 elements heavier than zinc (Z = 30) produced by neutron-capture reactions. Previous studies determined that three of these stars (the “r+s group”) have an enhancement of s-process material relative to the other three stars (the “r-only group”). We confirm that the r+s group is moderately enriched in Pb relative to the r-only group. Both groups of stars were born with the same amount of r-process material, but s-process material was also present in the gas from which the r+s group formed. The s-process abundances are inconsistent with predictions for asymptotic giant branch (AGB) stars with M ⩽ 3 M_☉ and suggest an origin in more massive AGB stars capable of activating the ²²Ne(α,n)²⁵Mg reaction. We calculate the s-process “residual” by subtracting the r-process pattern in the r-only group from the abundances in the r+s group. In contrast to previous r- and s-process decompositions, this approach makes no assumptions about the r- and s-process distributions in the solar system and provides a unique opportunity to explore s-process yields in a metal-poor environment.

We develop a general method to fit the underlying planetary distribution function (PLDF) to exoplanet survey data. This maximum likelihood method accommodates more than one planet per star and any number of planet or target star properties. We apply the method to announced Kepler planet candidates that transit solar-type stars. The Kepler team's estimates of the detection efficiency are used and are shown to agree with theoretical predictions for an ideal transit survey. The PLDF is fit to a joint power law in planet radius, down to 0.5 R_⊕, and orbital period, up to 50 days. The estimated number of planets per star in this sample is ∼0.7–1.4, where the range covers systematic uncertainties in the detection efficiency. To analyze trends in the PLDF we consider four planet samples, divided between shorter and longer periods at 7 days and between large and small radii at 3 R_⊕. The size distribution changes appreciably between these four samples, revealing a relative deficit of ∼3 R_⊕ planets at the shortest periods. This deficit is suggestive of preferential evaporation and sublimation of Neptune- and Saturn-like planets. If the trend and explanation hold, it would be spectacular observational support of the core accretion and migration hypotheses, and would allow refinement of these theories.

We present Spitzer/Infrared Spectrograph spectra of 31 T Tauri stars (TTS) and IRAM/1.3 mm observations for 34 low- and intermediate-mass stars in the Cep OB2 region. Including our previously published data, we analyze 56 TTS and 3 intermediate-mass stars with silicate features in Tr 37 (∼4 Myr) and NGC 7160 (∼12 Myr). The silicate emission features are well reproduced with a mixture of amorphous (with olivine, forsterite, and silica stoichiometry) and crystalline grains (forsterite, enstatite). We explore grain size and disk structure using radiative transfer disk models, finding that most objects have suffered substantial evolution (grain growth, settling). About half of the disks show inside-out evolution, with either dust-cleared inner holes or a radially dependent dust distribution, typically with larger grains and more settling in the innermost disk. The typical strong silicate features nevertheless require the presence of small dust grains, and could be explained by differential settling according to grain size, anomalous dust distributions, and/or optically thin dust populations within disk gaps. M-type stars tend to have weaker silicate emission and steeper spectral energy distributions than K-type objects. The inferred low dust masses are in a strong contrast with the relatively high gas accretion rates, suggesting global grain growth and/or an anomalous gas-to-dust ratio. Transition disks in the Cep OB2 region display strongly processed grains, suggesting that they are dominated by dust evolution and settling. Finally, the presence of rare but remarkable disks with strong accretion at old ages reveals that some very massive disks may still survive to grain growth, gravitational instabilities, and planet formation.

We present the preliminary analysis of over 1739 known and 349 candidate Jovian Trojans observed by the NEOWISE component of the Wide-field Infrared Survey Explorer (WISE). With this survey the available diameters, albedos, and beaming parameters for the Jovian Trojans have been increased by more than an order of magnitude compared to previous surveys. We find that the Jovian Trojan population is very homogenous for sizes larger than ∼10 km (close to the detection limit of WISE for these objects). The observed sample consists almost exclusively of low albedo objects, having a mean albedo value of 0.07 ± 0.03. The beaming parameter was also derived for a large fraction of the observed sample, and it is also very homogenous with an observed mean value of 0.88 ± 0.13. Preliminary debiasing of the survey shows that our observed sample is consistent with the leading cloud containing more objects than the trailing cloud. We estimate the fraction to be N(leading)/N(trailing) ∼ 1.4 ± 0.2, lower than the 1.6 ± 0.1 value derived by Szabó et al.

In the solar wind, when the effects of proton–proton Coulomb collisions are negligible, alpha particles usually flow faster than the protons in such a way that the differential alpha–proton flow velocity V_d = V_α − V_p is on the order of the Alfvén speed, is directed away from the Sun, and is nearly aligned with the local mean magnetic field. When this differential flow is taken into account, solutions of the hot plasma dispersion relation show that for the parallel propagating electromagnetic ion cyclotron (EMIC) instability driven by the proton temperature anisotropy T_⊥p > T_∥p, the maximum growth rate occurs in the +V_d direction and for the parallel firehose instability driven by the opposite proton temperature anisotropy T_∥p > T_⊥p, the maximum growth rate occurs in the −V_d direction. Thus, the EMIC instability preferentially generates left circularly polarized Alfvén-ion-cyclotron waves propagating away from the Sun and the parallel firehose instability preferentially generates right circularly polarized magnetosonic-whistler waves propagating toward the Sun with the maximum growth rates occurring for frequencies on the order of the proton cyclotron frequency and wavenumbers on the order of the proton inertial length. Because of the Doppler shift caused by the motion of the solar wind, both types of waves are left circularly polarized in the spacecraft frame for observations taken when the local mean magnetic field is collinear with the solar wind flow velocity. Theoretical investigation of these instabilities also shows that regions of parameter space exist where the unstable waves are generated propagating unidirectionally such as, for the EMIC instability for example, when the temperature anisotropy is small |(T_⊥p/T_∥p) − 1| < 1. Taken together, the above properties can explain the origin of parallel propagating electromagnetic waves recently observed near the proton inertial length in high-speed solar wind. The observed waves are most likely produced in situ by these instabilities. A remarkable property of the proposed mechanism that may be of practical importance is that the magnetic helicity of the unstable waves has the same sign no matter whether the proton temperature anisotropy (T_p⊥/T_p∥) − 1 is positive or negative.

This work presents the first quantitative composite model atmosphere analysis of Capella, the brightest near-equal-mass spectroscopic binary and principal star of the constellation Auriga. Its high-resolution spectrum leads to a slightly metal-rich object at [Fe/H] = +0.05 ± 0.08 dex. In line with its young age and its kinematics, this consistently associates Capella with the Hyades moving group. The measured projected rotational velocities, vsin i_Aa = 3.5 ± 0.8 km s⁻¹ and vsin i_Ab = 35.4 ± 3.2 km s⁻¹, both agree with rotational and orbital coplanarity and synchronous orbital rotation for the Aa component. At an orbital period P = 104 d the primary's bound rotation together with the almost zero orbital eccentricity are both key characteristics of this binary and clearly imply that the Aa component must have passed the tip of the giant branch. Whether in that phase Capella also became a mass transfer system remains inconclusive at present, though the high rotational velocity of the less evolved Hertzsprung gap secondary and the very diverse lithium abundances of both its components render this a plausible case.

We report on the observation of γ-rays above 25 GeV from the Crab pulsar (PSR B0532+21) using the MAGIC I telescope. Two data sets from observations during the winter period 2007/2008 and 2008/2009 are used. In order to discuss the spectral shape from 100 MeV to 100 GeV, one year of public Fermi Large Area Telescope (Fermi-LAT) data are also analyzed to complement the MAGIC data. The extrapolation of the exponential cutoff spectrum determined with the Fermi-LAT data is inconsistent with MAGIC measurements, which requires a modification of the standard pulsar emission models. In the energy region between 25 and 100 GeV, the emission in the P1 phase (from −0.06 to 0.04, location of the main pulse) and the P2 phase (from 0.32 to 0.43, location of the interpulse) can be described by power laws with spectral indices of −3.1 ± 1.0_stat ± 0.3_syst and −3.5 ± 0.5_stat ± 0.3_syst, respectively. Assuming an asymmetric Lorentzian for the pulse shape, the peak positions of the main pulse and the interpulse are estimated to be at phases −0.009 ± 0.007 and 0.393 ± 0.009, while the full widths at half-maximum are 0.025 ± 0.008 and 0.053 ± 0.015, respectively.

X-ray absorption line spectroscopy has recently shown evidence for previously unknown Ultra-fast Outflows (UFOs) in radio-quiet active galactic nuclei (AGNs). These have been detected essentially through blueshifted Fe xxv/xxvi K-shell transitions. In the previous paper of this series we defined UFOs as those highly ionized absorbers with an outflow velocity higher than 10,000 km s⁻¹ and assessed the statistical significance of the associated blueshifted absorption lines in a large sample of 42 local radio-quiet AGNs observed with XMM-Newton. The present paper is an extension of that work. First, we report a detailed curve of growth analysis of the main Fe xxv/xxvi transitions in photoionized plasmas. Then, we estimate an average spectral energy distribution for the sample sources and directly model the Fe K absorbers in the XMM-Newton spectra with the detailed Xstar photoionization code. We confirm that the frequency of sources in the radio-quiet sample showing UFOs is >35% and that the majority of the Fe K absorbers are indeed associated with UFOs. The outflow velocity distribution spans from ∼10,000 km s⁻¹ (∼0.03c) up to ∼100,000 km s⁻¹ (∼0.3c), with a peak and mean value of ∼42,000 km s⁻¹ (∼0.14c). The ionization parameter is very high and in the range log ξ ∼ 3–6 erg s⁻¹ cm, with a mean value of log ξ ∼ 4.2 erg s⁻¹ cm. The associated column densities are also large, in the range N_H ∼ 10²²–10²⁴ cm⁻², with a mean value of N_H ∼ 10²³ cm⁻². We discuss and estimate how selection effects, such as those related to the limited instrumental sensitivity at energies above 7 keV, may hamper the detection of even higher velocities and higher ionization absorbers. We argue that, overall, these results point to the presence of extremely ionized and possibly almost Compton-thick outflowing material in the innermost regions of AGNs. This also suggests that UFOs may potentially play a significant role in the expected cosmological feedback from AGNs and their study can provide important clues on the connection between accretion disks, winds, and jets.

Nuclear starbursts may contribute to the obscuration of active galactic nuclei (AGNs). The predicted star formation rates (SFRs) are modest, and, for the obscured AGNs that form the X-ray background at z < 1, the associated faint radio emission lies just beyond the sensitivity limits of the deepest surveys. Here, we search for this level of star formation by studying a sample of 359 X-ray-selected AGNs at z < 1 from the Cosmic Evolution Survey field that are not detected by current radio surveys. The AGNs are separated into bins based on redshift, X-ray luminosity, obscuration, and mid-infrared characteristics. An estimate of the AGN contribution to the radio flux density is subtracted from each radio image, and the images are then stacked to uncover any residual faint radio flux density. All of the bins containing 24 μm detected AGNs are detected with a signal-to-noise >3σ in the stacked radio images. In contrast, AGNs not detected at 24 μm are not detected in the resulting stacked radio images. This result provides strong evidence that the stacked radio signals are likely associated with star formation. The estimated SFRs derived from the radio stacks range from 3  M_☉ yr⁻¹ to 29  M_☉ yr⁻¹. Although it is not possible to associate the radio emission with a specific region of the host galaxies, these results are consistent with the predictions of nuclear starburst disks in AGN host galaxies.

The Baldwin, Phillips, and Terlevich emission-line ratio diagnostic ([O iii]/Hβ versus [N ii]/Hα, hereafter BPT diagram) efficiently separates galaxies whose signal is dominated by star formation (BPT-SF) from those dominated by active galactic nucleus (AGN) activity (BPT-AGN). Yet this BPT diagram is limited to z < 0.5, the redshift at which [N ii]λ6584 leaves the optical spectral window. Using the Sloan Digital Sky Survey (SDSS), we construct a new diagnostic, or TBT diagram, that is based on rest-frame g − z color, [Ne iii]λ3869, and [O ii]λλ3726 + 3729 and can be used for galaxies out to z < 1.4. The TBT diagram identifies 98.7% of the SDSS BPT-AGN as TBT-AGN and 97% of the SDSS BPT-SF as TBT-SF. Furthermore, it identifies 97% of the OPTX Chandra X-ray-selected AGNs as TBT-AGN. This is in contrast to the BPT diagram, which misidentifies 20% of X-ray-selected AGNs as BPT-SF. We use the Great Observatories Origins Deep Survey North and Lockman Hole galaxy samples, with their accompanying deep Chandra imaging, to perform X-ray and infrared stacking analyses to further validate our TBT-AGN and TBT-SF selections; that is, we verify the dominance of AGN activity in the former and star formation activity in the latter. Finally, we address the inclusion of the majority of the BPT-comp (sources lying between the BPT-SF and BPT-AGN regimes) in our TBT-AGN regime. We find that the stacked BPT-comp source is X-ray hard (〈Γ_eff〉 = 1.0^+0.4_−0.4) and has a high X-ray luminosity to total infrared luminosity ratio. This suggests that, on average, the X-ray signal in BPT-comp is dominated by obscured or low accretion rate AGN activity rather than by star formation, supporting their inclusion in the TBT-AGN regime.

An extreme case of electron shock drift acceleration (SDA) in low Mach number collisionless shocks is investigated as a plausible mechanism for the initial acceleration of relativistic electrons in large-scale shocks in galaxy clusters, where the upstream plasma temperature is of the order of 10 keV and the degree of magnetization is not too small. One-dimensional electromagnetic full particle simulations reveal that, even when a shock is rather moderate, a part of the thermal incoming electrons are accelerated and reflected through relativistic SDA and form a local non-thermal population just upstream of the shock. The accelerated electrons can self-generate local coherent waves and further be back-scattered toward the shock by those waves. This may be a scenario for the first stage of the electron shock acceleration occurring at the large-scale shocks in galaxy clusters, such as CIZA J2242.8+5301, which have well-defined radio relics.

We report on the serendipitous discovery in the Blanco Cosmology Survey (BCS) imaging data of a z = 0.9057 galaxy that is being strongly lensed by a massive galaxy cluster at a redshift of z = 0.3838. The lens (BCS J2352−5452) was discovered while examining i- and z-band images being acquired in 2006 October during a BCS observing run. Follow-up spectroscopic observations with the Gemini Multi-Object Spectrograph instrument on the Gemini-South 8 m telescope confirmed the lensing nature of this system. Using weak-plus-strong lensing, velocity dispersion, cluster richness N₂₀₀, and fitting to a Navarro–Frenk–White (NFW) cluster mass density profile, we have made three independent estimates of the mass M₂₀₀ which are all very consistent with each other. The combination of the results from the three methods gives M₂₀₀ = (5.1 ± 1.3) × 10¹⁴ M_☉, which is fully consistent with the individual measurements. The final NFW concentration c₂₀₀ from the combined fit is c₂₀₀ = 5.4^+1.4_{− 1.1}. We have compared our measurements of M₂₀₀ and c₂₀₀ with predictions for (1) clusters from ΛCDM simulations, (2) lensing-selected clusters from simulations, and (3) a real sample of cluster lenses. We find that we are most compatible with the predictions for ΛCDM simulations for lensing clusters, and we see no evidence based on this one system for an increased concentration compared to ΛCDM. Finally, using the flux measured from the [O ii]3727 line we have determined the star formation rate of the source galaxy and find it to be rather modest given the assumed lens magnification.

A comprehensive search for variable and transient radio sources has been conducted using ∼55,000 snapshot images of the Faint Images of the Radio Sky at Twenty-cm survey. We present an analysis leading to the discovery of 1627 variable and transient objects down to mJy levels over a wide range of timescales (a few minutes to years). Variations observed range from 20% to a factor of 25. Multi-wavelength matching for counterparts reveals the diverse classes of objects exhibiting variability, ranging from nearby stars and pulsars to galaxies and distant quasars. Interestingly, more than half of the objects in the sample have either no classified counterparts or no corresponding sources at any other wavelength and require multi-wavelength follow-up observations. We discuss these classes of variables and speculate on the identity of objects that lack multi-wavelength counterparts.

The ionized core in the Sgr B2 Main star-forming region was imaged using the Submillimeter Array archival data observed for the H26α line and continuum emission at 0.86 mm with an angular resolution 03. Eight hyper-compact H26α emission sources were detected with a typical size in the range of 1.6–20 × 10² AU and electron density of 0.3–3 × 10⁷ cm⁻³, corresponding to the emission measure 0.4–8.4 × 10¹⁰ cm⁻⁶ pc. The H26α line fluxes from the eight hyper-compact H ii sources imply that the ionization for each of the sources must be powered by a Lyman continuum flux from an O star or a cluster of B stars. The most luminous H26α source among the eight detected sources requires an O6 star that appears to be embedded in the ultra-compact H ii region F3. In addition, ∼23 compact continuum emission sources were also detected within the central 5″× 3″ (∼0.2 pc) region. Under the assumption of a power-law distribution for the dust temperature, with the observed brightness temperature of the dust emission we determined the physical properties of the submillimeter emission sources, showing that the molecular densities are in the range of 1–10 × 10⁸ cm⁻³, surface densities between 13 and 150 g cm⁻², and total gas masses in the range from 5 to ≳ 200 M_☉, which are one or two orders of magnitude greater than the corresponding values of the Bonnor–Ebert mass. With a mean free-fall timescale of 2 × 10³ years, each of the massive protostellar cores is undergoing gravitational collapse to form new massive stars in the Sgr B2 Main core.

Currently three isolated radio pulsars and one binary radio pulsar with no evidence of any previous recycling are known in 97 surveyed Galactic globular clusters (GCs). As pointed out by Lyne et al., the presence of these pulsars cannot be explained by core-collapse supernovae, as commonly assumed for their counterparts in the Galactic disk. We apply a Bayesian analysis to the results from surveys for radio pulsars in GCs and find the number of potentially observable non-recycled radio pulsars present in all clusters to be <3600. Accounting for beaming and retention considerations, the implied birthrate for any formation scenario for all 97 clusters is <0.25 pulsars century⁻¹ assuming a Maxwellian distribution of velocities with a dispersion of 10 km s⁻¹. The implied birthrates for higher velocity dispersions are substantially higher than inferred for such pulsars in the Galactic disk. This suggests that the velocity dispersion of young pulsars in GCs is significantly lower than those of disk pulsars. These numbers may be substantial overestimates due to the fact that the currently known sample of young pulsars is observed only in metal-rich clusters. We propose that young pulsars may only be formed in GCs with metallicities with log[Fe/H] > − 0.6. In this case, the potentially observable population of such young pulsars is 447⁺¹⁴²⁰₋₃₉₉ (the error bars give a 95% confidence interval) and their birthrate is 0.012^+0.037_−0.010 pulsars century⁻¹. The most likely creation scenario to explain these pulsars is the electron capture supernova of an OMgNe white dwarf.

In this paper, an attempt is made to define the subject of photoionizational plasmas through rigorous mathematical formalism. The central results of this paper are the following. (1) A set of recursive equations is introduced for the computation of the charge state distributions in photoionizational plasmas. (2) Quantitative validity limits are given for both the collisional and the photoionizational domains. (3) A parameter that determines the charge state distribution in the photoionizational regime is introduced. (4) We provide detailed discussion about the most important components of the emission spectrum in the different equilibrium domains of the emitting plasma. Some of these components have not been reported so far as included in the analysis of such plasmas.

A new computer code, PhiCRE, has been developed to calculate the ionization and population distributions in a photoionizational–collisional-radiative plasma. Comparisons with experiments show that the present code provides rather accurate ionization distributions in photoionized plasmas and show reasonable agreement with other codes. Using this code, we have carried out a systematic study of the behavior of the charge state distributions and the average charge as a function of several parameters of the incident radiation and the plasma parameters.

We present a comprehensive abundance analysis of 20 elements for 16 new low-metallicity stars from the Chemical Abundances of Stars in the Halo (CASH) project. The abundances have been derived from both Hobby-Eberly Telescope High Resolution Spectrograph snapshot spectra (R ∼15, 000) and corresponding high-resolution (R ∼35, 000) Magellan Inamori Kyocera Echelle spectra. The stars span a metallicity range from [Fe/H] from −2.9 to −3.9, including four new stars with [Fe/H] < −3.7. We find four stars to be carbon-enhanced metal-poor (CEMP) stars, confirming the trend of increasing [C/Fe] abundance ratios with decreasing metallicity. Two of these objects can be classified as CEMP-no stars, adding to the growing number of these objects at [Fe/H]< − 3. We also find four neutron-capture-enhanced stars in the sample, one of which has [Eu/Fe] of 0.8 with clear r-process signatures. These pilot sample stars are the most metal-poor ([Fe/H] ≲ −3.0) of the brightest stars included in CASH and are used to calibrate a newly developed, automated stellar parameter and abundance determination pipeline. This code will be used for the entire ∼500 star CASH snapshot sample. We find that the pipeline results are statistically identical for snapshot spectra when compared to a traditional, manual analysis from a high-resolution spectrum.

We report on the detection of a third massive star component in the σ Orionis AB system, traditionally considered as a binary system. The system has been monitored by the IACOB Spectroscopic Survey of Northern Massive Stars program, obtaining 23 high-resolution FIES@NOT spectra with a time span of ∼2.5 years. The analysis of the radial velocity curves of the two spectroscopic components observed in the spectra has allowed us to obtain the orbital parameters of the system, resulting in a high eccentric orbit (e ∼ 0.78) with an orbital period of 143.5 ± 0.5 days. This result implies the actual presence of three stars in the σ Orionis AB system when combined with previous results obtained from the study of the astrometric orbit (with an estimated period of ∼157 years).

Observations indicate that outflows from massive young stars are more collimated during their early evolution compared to later stages. Our paper investigates various physical processes that impact the outflow dynamics, i.e., its acceleration and collimation. We perform axisymmetric magnetohydrodynamic (MHD) simulations particularly considering the radiation pressure exerted by the star and the disk. We have modified the PLUTO code to include radiative forces in the line-driving approximation. We launch the outflow from the innermost disk region (r < 50 AU) by magnetocentrifugal acceleration. In order to disentangle MHD effects from radiative forces, we start the simulation in pure MHD and later switch on the radiation force. We perform a parameter study considering different stellar masses (thus luminosity), magnetic flux, and line-force strength. For our reference simulation—assuming a 30 M_☉ star—we find substantial de-collimation of 35% due to radiation forces. The opening angle increases from 20° to 32° for stellar masses from 20 M_☉ to 60 M_☉. A small change in the line-force parameter α from 0.60 to 0.55 changes the opening angle by ∼8°. We find that it is mainly the stellar radiation that affects the jet dynamics. Unless the disk extends very close to the star, its force is too small to have much impact. Essentially, our parameter runs with different stellar masses can be understood as a proxy for the time evolution of the star–outflow system. Thus, we have shown that when the stellar mass (thus luminosity) increases with age, the outflows become less collimated.

We made C¹⁸O (2–1) and CS (7–6) images of the protostellar envelope around B335 with a high spatial dynamic range from ∼10,000 to ∼400 AU by combining the Submillimeter Array and single-dish data. The C¹⁸O emission shows an extended (∼10,000 AU) structure as well as a compact (∼1500 AU) component concentrated at the protostellar position. The CS emission shows a compact (∼900 AU) component surrounding the protostar, plus a halo-like (∼3000 AU) structure elongated along the east–west direction. At higher velocities (|ΔV| ≳ 0.3 km s⁻¹), the CS emission is stronger and more extended than the C¹⁸O emission. Physical conditions of the envelope were examined through a Large Velocity Gradient model. At |ΔV| ≳ 0.3 km s⁻¹, the gas temperature is higher (>40 K) than that at |ΔV| ≲ 0.3 km s⁻¹, whereas the gas density is lower (<10⁶ cm⁻³). We consider that the higher temperature and lower density gas at |ΔV| ≳ 0.3 km s⁻¹ is related to the associated outflow, while the lower temperature and higher density gas at |ΔV| ≲ 0.3 km s⁻¹ is the envelope component. From the inspection of the positional offsets in the velocity channel maps, the radial profile of the specific angular momentum of the envelope rotation in B335 was revealed at radii from ∼10⁴ down to ∼10² AU. The specific angular momentum decreases down to a radius of ∼370 AU, and then appears to be conserved within that radius. A possible scenario of the evolution of envelope rotation is discussed.

We present Green Bank Telescope observations of the 3₁₂−3₁₃ (29 GHz) and 4₁₃−4₁₄ (48 GHz) transitions of the H₂CO molecule toward a sample of 23 well-studied star-forming regions. Analysis of the relative intensities of these transitions can be used to reliably measure the densities of molecular cores. Adopting kinetic temperatures from the literature, we have employed a large velocity gradient (LVG) model to derive the average hydrogen number density (n(H₂)) within a 16″ beam toward each source. Densities in the range of 10^5.5–10^6.5 cm⁻³ and ortho-formaldehyde column densities per unit line width between 10^13.5 and 10^14.5 cm⁻² (km s⁻¹)⁻¹ are found for most objects, in general agreement with existing measurements. A detailed analysis of the advantages and limitations to this densitometry technique is also presented. We find that H₂CO 3₁₂−3₁₃/4₁₃−4₁₄ densitometry proves to be best suited to objects with T_K ≳ 100 K, above which the H₂CO LVG models become relatively independent of kinetic temperature. This study represents the first detection of these H₂CO K-doublet transitions in all but one object in our sample. The ease with which these transitions were detected, coupled with their unique sensitivity to spatial density, makes them excellent monitors of density in molecular clouds for future experiments. We also report the detection of the 9₂–8₁A⁻ (29 GHz) transition of CH₃OH toward six sources.

We report the discovery of two exoplanets transiting high-jitter stars. HAT-P-32b orbits the bright V = 11.289 late-F–early-G dwarf star GSC 3281-00800, with a period P = 2.150008 ± 0.000001 d. The stellar and planetary masses and radii depend on the eccentricity of the system, which is poorly constrained due to the high-velocity jitter (∼80 m s⁻¹). Assuming a circular orbit, the star has a mass of 1.16 ± 0.04 M_☉ and radius of 1.22 ± 0.02 R_☉, while the planet has a mass of 0.860 ± 0.164 M_J and a radius of 1.789 ± 0.025 R_J. The second planet, HAT-P-33b, orbits the bright V = 11.188 late-F dwarf star GSC 2461-00988, with a period P = 3.474474 ± 0.000001 d. As for HAT-P-32, the stellar and planetary masses and radii of HAT-P-33 depend on the eccentricity, which is poorly constrained due to the high jitter (∼50 m s⁻¹). In this case, spectral line bisector spans (BSs) are significantly anti-correlated with the radial velocity residuals, and we are able to use this correlation to reduce the residual rms to ∼35 m s⁻¹. We find that the star has a mass of 1.38 ± 0.04 M_☉ and a radius of 1.64 ± 0.03 R_☉ while the planet has a mass of 0.762 ± 0.101 M_J and a radius of 1.686 ± 0.045 R_J for an assumed circular orbit. Due to the large BS variations exhibited by both stars we rely on detailed modeling of the photometric light curves to rule out blend scenarios. Both planets are among the largest radii transiting planets discovered to date.

We present the results of a pilot survey for neutral hydrogen (H i) 21 cm absorption in the Arecibo Legacy Fast Arecibo L-Band Feed Array (ALFALFA) Survey. This project is a wide-area “blind” search for H i absorption in the local universe, spanning −650 km s⁻¹ < cz < 17, 500 km s⁻¹ and covering 517.0 deg² (7% of the full ALFALFA survey). The survey is sensitive to H i absorption lines stronger than 7.7 mJy (8983 radio sources) and is 90% complete for lines stronger than 11.0 mJy (7296 sources). The total redshift interval sensitive to all damped Lyα (DLA) systems ( cm⁻²) is Δz = 7.0 (129 objects, assuming T_s = 100 K and covering fraction unity); for super-DLAs ( cm⁻²) it is Δz = 128.2 (2353 objects). We re-detect the intrinsic H i absorption line in UGC 6081 but detect no intervening absorption line systems. We compute a 95% confidence upper limit on the column density frequency distribution function spanning four orders of magnitude in column density, 10¹⁹ (T_s/100 K) (1/f) cm cm⁻², that is consistent with previous redshifted optical DLA surveys and the aggregate H i 21 cm emission in the local universe. The detection rate is in agreement with extant observations. This pilot survey suggests that an absorption line search of the complete ALFALFA survey—or any higher redshift, larger bandwidth, or more sensitive survey, such as those planned for Square Kilometer Array pathfinders or a low-frequency lunar array—will either make numerous detections or will set a strong statistical lower limit on the typical spin temperature of neutral hydrogen gas.