Table of contents

We use GOODS and CANDELS images to identify progenitors of massive (M > 10¹⁰ M_☉) compact early-type galaxies (ETGs) at z ∼ 1.6. Because merging and accretion increase the size of the stellar component of galaxies, if the progenitors are among known star-forming galaxies, these must be compact themselves. We select candidate progenitors among compact Lyman-break galaxies at z ∼ 3 on the basis of their mass, star-formation rate (SFR), and central stellar density, and we find that these account for a large fraction of, and possibly all, compact ETGs at z ∼ 1.6. We find that the average far-UV spectral energy distribution (SED) of the candidates is redder than that of the non-candidates, but the optical and mid-IR SED are the same, implying that the redder UV of the candidates is inconsistent with larger dust obscuration and consistent with more evolved (aging) star formation. This is in line with other evidence suggesting that compactness is a sensitive predictor of passivity among high-redshift massive galaxies. We also find that the light distribution of both the compact ETGs and their candidate progenitors does not show any extended "halos" surrounding the compact "core,"both in individual images and in stacks. We argue that this is generally inconsistent with the morphology of merger remnants, even if gas rich, as predicted by N-body simulations. This suggests that the compact ETGs formed via highly dissipative, mostly gaseous accretion of units whose stellar components are very small and undetected in the Hubble Space Telescope images, with their stellar mass assembling in situ, and that they have not experienced any major merging until the epoch of observations at z ∼ 1.6.

Energy-changing electron–hydrogen atom collisions are crucial to regulating the energy balance in astrophysical and laboratory plasmas and are relevant to the formation of stellar atmospheres, recombination in H ii clouds, primordial recombination, three-body recombination, and heating in ultracold and fusion plasmas. Computational modeling of electron–hydrogen collision has been attempted through quantum mechanical scattering state-to-state calculations of transitions involving low-lying energy levels in hydrogen (with principal quantum number n < 7) and at large principal quantum numbers using classical trajectory techniques. Analytical expressions are proposed that interpolate the current quantum mechanical and classical trajectory results for electron–hydrogen scattering in the entire range of energy levels for nearly the entire temperature range of interest in astrophysical environments. An asymptotic expression for the Born cross section is interpolated with a modified expression previously derived for electron–hydrogen scattering in the Rydberg regime using classical trajectory Monte Carlo simulations. The derived formula is compared to existing numerical data for transitions involving low principal quantum numbers, and the dependence of the deviations on temperature is discussed.

The magnetosphere of a rotating pulsar naturally develops a current sheet (CS) beyond the light cylinder (LC). Magnetic reconnection in this CS inevitably dissipates a nontrivial fraction of the pulsar spin-down power within a few LC radii. We develop a basic physical picture of reconnection in this environment and discuss its implications for the observed pulsed gamma-ray emission. We argue that reconnection proceeds in the plasmoid-dominated regime, via a hierarchical chain of multiple secondary islands/flux ropes. The inter-plasmoid reconnection layers are subject to strong synchrotron cooling, leading to significant plasma compression. Using the conditions of pressure balance across these current layers, the balance between the heating by magnetic energy dissipation and synchrotron cooling, and Ampere's law, we obtain simple estimates for key parameters of the layers—temperature, density, and layer thickness. In the comoving frame of the relativistic pulsar wind just outside of the equatorial CS, these basic parameters are uniquely determined by the strength of the reconnecting upstream magnetic field. For the case of the Crab pulsar, we find them to be of order 10 GeV, 10¹³ cm⁻³, and 10 cm, respectively. After accounting for the bulk Doppler boosting due to the pulsar wind, the synchrotron and inverse-Compton emission from the reconnecting CS can explain the observed pulsed high-energy (GeV) and very high energy (∼100 GeV) radiation, respectively. Also, we suggest that the rapid relative motions of the secondary plasmoids in the hierarchical chain may contribute to the production of the pulsar radio emission.

We investigate formation mechanisms for icy super-Earth-mass planets orbiting at 2–20 AU around 0.1–0.5 M_☉ stars. A large ensemble of coagulation calculations demonstrates a new formation channel: disks composed of large planetesimals with radii of 30–300 km form super-Earths on timescales of ∼1 Gyr. In other gas-poor disks, a collisional cascade grinds planetesimals to dust before the largest planets reach super-Earth masses. Once icy Earth-mass planets form, they migrate through the leftover swarm of planetesimals at rates of 0.01–1 AU Myr⁻¹. On timescales of 10 Myr to 1 Gyr, many of these planets migrate through the disk of leftover planetesimals from semimajor axes of 5–10 AU to 1–2 AU. A few percent of super-Earths might migrate to semimajor axes of 0.1–0.2 AU. When the disk has an initial mass comparable with the minimum-mass solar nebula, scaled to the mass of the central star, the predicted frequency of super-Earths matches the observed frequency.

The Sun's polar magnetic fields are directly related to solar cycle variability. The strength of the polar fields at the start (minimum) of a cycle determine the subsequent amplitude of that cycle. In addition, the polar field reversals at cycle maximum alter the propagation of galactic cosmic rays throughout the heliosphere in fundamental ways. We describe a surface magnetic flux transport model that advects the magnetic flux emerging in active regions (sunspots) using detailed observations of the near-surface flows that transport the magnetic elements. These flows include the axisymmetric differential rotation and meridional flow and the non-axisymmetric cellular convective flows (supergranules), all of which vary in time in the model as indicated by direct observations. We use this model with data assimilated from full-disk magnetograms to produce full surface maps of the Sun's magnetic field at 15 minute intervals from 1996 May to 2013 July (all of sunspot cycle 23 and the rise to maximum of cycle 24). We tested the predictability of this model using these maps as initial conditions, but with daily sunspot area data used to give the sources of new magnetic flux. We find that the strength of the polar fields at cycle minimum and the polar field reversals at cycle maximum can be reliably predicted up to 3 yr in advance. We include a prediction for the cycle 24 polar field reversal.

Ultraluminous X-ray sources (ULXs) are some of the brightest phenomena found outside of a galaxy's nucleus, and their explanation typically invokes accretion of material onto a black hole. Here, we perform the largest population study to date of ULXs in early-type galaxies, focusing on whether a galaxy's large-scale environment can affect its ULX content. Using the AMUSE survey, which includes homogeneous X-ray coverage of 100 elliptical galaxies in the Virgo cluster and a similar number of elliptical galaxies in the field (spanning stellar masses of 10⁸–10¹² M_☉), we identify 37.9 ± 10.1 ULXs in Virgo and 28.1 ± 8.7 ULXs in the field. Across both samples, we constrain the number of ULXs per unit stellar mass, i.e., the ULX specific frequency, to be 0.062 ± 0.013 ULXs per 10¹⁰ M_☉ (or about 1 ULX per 1.6 × 10¹¹ M_☉ of galaxy stellar mass). We find that the number of ULXs, the specific frequency of ULXs, and the average ULX spectral properties are all similar in both cluster and field environments. Contrary to late-type galaxies, we do not see any trend between specific ULX frequency and host galaxy stellar mass, and we show that dwarf ellipticals host fewer ULXs than later-type dwarf galaxies at a statistically meaningful level. Our results are consistent with ULXs in early-type galaxies probing the luminous tail of the low-mass X-ray binary population, and are briefly discussed in context of the influence of gravitational interactions on the long-term evolution of a galaxy's (older) stellar population.

We present 20 candidate hypervelocity stars from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) G and K dwarf samples. Previous searches for hypervelocity stars have only focused on large radial velocities; in this study, we also use proper motions to select the candidates. We determine the hypervelocity likelihood of each candidate by means of Monte Carlo simulations, considering the significant errors often associated with high proper motion stars. We find that nearly half of the candidates exceed their escape velocities with at least 98% probability. Every candidate also has less than a 25% chance of being a high-velocity fluke within the SEGUE sample. Based on orbits calculated using the observed six-dimensional positions and velocities, few, if any, of these candidates originate from the Galactic center. If these candidates are truly hypervelocity stars, they were not ejected by interactions with the Milky Way's supermassive black hole. This calls for a more serious examination of alternative hypervelocity-star ejection scenarios.

Photodesorption from a crystalline film of CO₂(ice) at 75 K has been studied using Lyα (10.2 eV) radiation. We combine quantitative mass spectrometric studies of gases evolved and transmission IR studies of species trapped in the ice. Direct CO desorption is observed from the primary CO₂ photodissociation process, which occurs promptly for CO₂ molecules located on the outermost surface of the ice (Process I). As the fluence of Lyα radiation increases to ∼5.5 × 10¹⁷ photons cm⁻², extensive damage to the crystalline ice occurs and photo-produced CO molecules from deeper regions (Process II) are found to desorb at a rapidly increasing rate, which becomes two orders of magnitude greater than Process I. It is postulated that deep radiation damage to produce an extensive amorphous phase of CO₂ occurs in the 50 nm ice film and that CO (and CO₂) diffusive transport is strongly enhanced in the amorphous phase. Photodesorption in Process II is a combination of electronic and thermally activated processes. Radiation damage in crystalline CO₂ ice has been monitored by its effects on the vibrational line shapes of CO₂(ice). Here the crystalline-to-amorphous phase transition has been correlated with the occurrence of efficient molecular transport over long distances through the amorphous phase of CO₂(ice). Future studies of the composition of the interstellar region, generated by photodesorption from ice layers on grains, will have to consider the significant effects of radiation damage on photodesorption rates.

Observational confirmation of hot accretion model predictions has been hindered by the challenge to resolve spatially the Bondi radii of black holes with X-ray telescopes. Here, we use the Megasecond Chandra X-ray Visionary Project observation of the NGC 3115 supermassive black hole to place the first direct observational constraints on the spatially and spectroscopically resolved structures of the X-ray emitting gas inside the Bondi radius of a black hole. We measured temperature and density profiles of the hot gas from a fraction out to tens of the Bondi radius (R_B = 24–48 = 112–224 pc). The projected temperature jumps significantly from ∼0.3 keV beyond 5'' to ∼0.7 keV within ∼4''–5'', but then abruptly drops back to ∼0.3 keV within ∼3''. This is contrary to the expectation that the temperature should rise toward the center for a radiatively inefficient accretion flow. A hotter thermal component of ∼1 keV inside 3'' (∼150 pc) is revealed using a two-component thermal model, with the cooler ∼0.3 keV thermal component dominating the spectra. We argue that the softer emission comes from diffuse gas physically located within ∼150 pc of the black hole. The density profile is broadly consistent with ρ∝r⁻¹ within the Bondi radius for either the single temperature or the two-temperature model. The X-ray data alone with physical reasoning argue against the absence of a black hole, supporting that we are witnessing the onset of the gravitational influence of the supermassive black hole.

We explore the relationship between dust-emission derived reddening E(B − V) and atomic hydrogen column density N(H i) derived from 21 cm emission surveys. We consider measurements at galactic latitudes |b| ≳ 20^o and E(B − V) ≲ 0.1 mag where the interstellar gas is predominantly neutral and atomic, and opacity corrections to 21 cm H i profiles are small. Over the Galaxy at large, at lower resolutions in H i, and on smaller scales at higher resolutions, we find that the reddening is always much smaller than would be expected from the usually quoted relation N(H) =5.8 × 10²¹  cm⁻²E(B − V)  based on stellar reddening and UV absorption toward early-type stars. On wide scales we find N(H i) = 8.3 × 10²¹  cm⁻²E(B − V). We cite various precedents for such a large N(H i)/E(B − V) ratio whenever wide-field 21 cm emission surveys are considered, including when reddening based on galaxy counts and colors is substituted for the dust-emission derived reddening measure.

The Galactic Bulge Survey (GBS) is a wide but shallow X-ray survey of regions above and below the Plane in the Galactic Bulge. It was performed using the Chandra X-ray Observatory's ACIS camera. The survey is primarily designed to find and classify low luminosity X-ray binaries. The combination of the X-ray depth of the survey and the accessibility of optical and infrared counterparts makes this survey ideally suited to identification of new symbiotic X-ray binaries (SyXBs) in the Bulge. We consider the specific case of the X-ray source CXOGBS J173620.2–293338. It is coincident to within 1 arcsec with a very red star, showing a carbon star spectrum and irregular variability in the Optical Gravitational Lensing Experiment data. We classify the star as a late C-R type carbon star based on its spectral features, photometric properties, and variability characteristics, although a low-luminosity C-N type cannot be ruled out. The brightness of the star implies it is located in the Bulge, and its photometric properties are overall consistent with the Bulge carbon star population. Given the rarity of carbon stars in the Bulge, we estimate the probability of such a close chance alignment of any GBS source with a carbon star to be ≲ 10⁻³, suggesting that this is likely to be a real match. If the X-ray source is indeed associated with the carbon star, then the X-ray luminosity is around 9 × 10³² erg s⁻¹. Its characteristics are consistent with a low luminosity SyXB, or possibly a low accretion rate white dwarf symbiotic.

In the internal shock model for gamma-ray bursts (GRBs), the synchrotron spectrum from the fast cooling electrons in a homogeneous downstream magnetic field (MF) is too soft to produce the low-energy slope of GRB spectra. However, the MF may decay downstream with distance from the shock front. Here we show that the synchrotron spectrum becomes harder if electrons undergo synchrotron and inverse-Compton cooling in a decaying MF. To reconcile this with the typical GRB spectrum with low-energy slope νF_ν∝ν, the postshock MF decay time must be comparable to the cooling time of the bulk electrons (corresponding to a MF decaying length typically of ∼10⁵ skin depths); that the inverse-Compton cooling should dominate synchrotron cooling after the MF decay time; and/or that the MF decays with comoving time roughly as B∝t^−1.5. An internal shock synchrotron model with a decaying MF can account for the majority of GRBs with low-energy slopes not harder than ν^4/3.

Fast Independent Component Analysis (FastICA) is a component separation algorithm based on the levels of non-Gaussianity. Here we apply FastICA to the component separation problem of the microwave background, including carbon monoxide (CO) line emissions that are found to contaminate the PLANCK High Frequency Instrument (HFI) data. Specifically, we prepare 100 GHz, 143 GHz, and 217 GHz mock microwave sky maps, which include galactic thermal dust, NANTEN CO line, and the cosmic microwave background (CMB) emissions, and then estimate the independent components based on the kurtosis. We find that FastICA can successfully estimate the CO component as the first independent component in our deflection algorithm because its distribution has the largest degree of non-Gaussianity among the components. Thus, FastICA can be a promising technique to extract CO-like components without prior assumptions about their distributions and frequency dependences.

A comprehensive approach is provided for the study of both S-type and P-type habitability in stellar binary systems, which in principle can also be expanded to systems of higher order. P-type orbits occur when the planet orbits both binary components, whereas in the case of S-type orbits, the planet orbits only one of the binary components with the second component considered a perturbator. The selected approach encapsulates a variety of different aspects, which include: (1) the consideration of a joint constraint, including orbital stability and a habitable region for a putative system planet through the stellar radiative energy fluxes ("radiative habitable zone"; RHZ), needs to be met; (2) the treatment of conservative, general, and extended zones of habitability for the various systems as defined for the solar system and beyond; (3) the provision of a combined formalism for the assessment of both S-type and P-type habitability; in particular, mathematical criteria are presented for the kind of system in which S-type and P-type habitability is realized; (4) applications of the attained theoretical approach to standard (theoretical) main-sequence stars. In principle, five different cases of habitability are identified, which are S-type and P-type habitability provided by the full extent of the RHZs; habitability, where the RHZs are truncated by the additional constraint of planetary orbital stability (referred to as ST- and PT-type, respectively); and cases of no habitability at all. Regarding the treatment of planetary orbital stability, we utilize the formulae of Holman & Wiegert as also used in previous studies. In this work, we focus on binary systems in circular orbits. Future applications will also consider binary systems in elliptical orbits and provide thorough comparisons to other methods and results given in the literature.

We present detailed extreme ultraviolet (EUV) spectra of four large solar flares: M5.6, X1.3, X3.4, and X17 classes in the spectral ranges 176–207 Å and 280–330 Å. These spectra were obtained by the slitless spectroheliograph SPIRIT onboard the CORONAS-F satellite. To our knowledge, these are the first detailed EUV spectra of large flares obtained with a spectral resolution of ∼0.1 Å. We performed a comprehensive analysis of the obtained spectra and provide identification of the observed spectral lines. The identification was performed based on the calculation of synthetic spectra (the CHIANTI database was used), with simultaneous calculations of the differential emission measure (DEM) and density of the emitting plasma. More than 50 intense lines are present in the spectra that correspond to a temperature range of T = 0.5–16 MK; most of the lines belong to Fe, Ni, Ca, Mg, and Si ions. In all the considered flares, intense hot lines from Ca xvii, Ca xviii, Fe xx, Fe xxii, and Fe xxiv are observed. The calculated DEMs have a peak at T ∼ 10 MK. The densities were determined using Fe xi–Fe xiii lines and averaged 6.5 × 10⁹ cm⁻³. We also discuss the identification, accuracy, and major discrepancies of the spectral line intensity prediction.

Using numerical simulations of charged-particles propagating in the heliospheric magnetic field, we study small-scale gradients, or "dropouts," in the intensity of solar energetic particles seen at 1 AU. We use two turbulence models, the foot-point random motion model and the two-component model, to generate fluctuating magnetic fields similar to spacecraft observations at 1 AU. The turbulence models include a Kolmogorov-like magnetic field power spectrum containing a broad range of spatial scales from those that lead to large-scale field-line random walk to small scales leading to resonant pitch-angle scattering of energetic particles. We release energetic protons (20 keV–10 MeV) from a spatially compact and instantaneous source. The trajectories of energetic charged particles in turbulent magnetic fields are numerically integrated. Spacecraft observations are mimicked by collecting particles in small windows when they pass the windows at a distance of 1 AU. We show that small-scale gradients in the intensity of energetic particles and velocity dispersions observed by spacecraft can be reproduced using the foot-point random motion model. However, no dropouts are seen in simulations using the two-component magnetic turbulence model. We also show that particle scattering in the solar wind magnetic field needs to be infrequent for intensity dropouts to form.

We present the results of a study to optimize the principal component analysis (PCA) algorithm for planet detection, a new algorithm complementing angular differential imaging and locally optimized combination of images (LOCI) for increasing the contrast achievable next to a bright star. The stellar point spread function (PSF) is constructed by removing linear combinations of principal components, allowing the flux from an extrasolar planet to shine through. The number of principal components used determines how well the stellar PSF is globally modeled. Using more principal components may decrease the number of speckles in the final image, but also increases the background noise. We apply PCA to Fomalhaut Very Large Telescope NaCo images acquired at 4.05 μm with an apodized phase plate. We do not detect any companions, with a model dependent upper mass limit of 13–18 M_Jup from 4–10 AU. PCA achieves greater sensitivity than the LOCI algorithm for the Fomalhaut coronagraphic data by up to 1 mag. We make several adaptations to the PCA code and determine which of these prove the most effective at maximizing the signal-to-noise from a planet very close to its parent star. We demonstrate that optimizing the number of principal components used in PCA proves most effective for pulling out a planet signal.

Recent observations suggest that some supernovae may be the result of an explosion into an optically thick circumstellar material, the product of pre-explosion mass loss (wind) by the progenitor star. This scenario has been studied previously both analytically and numerically. However, many previous studies base their analysis on the diffusion approximation for radiation transfer, which is inappropriate in the optically thin outer layers of the wind. Here we study the deviations from diffusion and calculate light curves more accurately using a Monte Carlo approach to photon transfer. We distinguish between "compact" winds, for which the diffusion approximation is appropriate, and "extended" winds, which require a more delicate treatment of the radiation. We show that this effect is more significant than that of the light-travel time difference to a distant observer, which has a secondary influence on the light curves of extended-wind systems. We also comment on the applicability of the widely used flux-limited diffusion approximation in this context: we find that it generally does not reproduce the Monte Carlo results. The flux-limited diffusion approximation leads to results that are not only quantitatively but also qualitatively wrong in the extended-wind regime.

We observed radio continuum emission in 27 local (D < 70 Mpc) star-forming galaxies with the Robert C. Byrd Green Bank Telescope between 26 GHz and 40 GHz using the Caltech Continuum Backend. We obtained detections for 22 of these galaxies at all four sub-bands and four more marginal detections by taking the average flux across the entire bandwidth. This is the first detection (full or marginal) at these frequencies for 22 of these galaxies. We fit spectral energy distributions (SEDs) for all of the four sub-band detections. For 14 of the galaxies, SEDs were best fit by a combination of thermal free–free and nonthermal synchrotron components. Eight galaxies with four sub-band detections had steep spectra that were only fit by a single nonthermal component. Using these fits, we calculated supernova rates, total number of equivalent O stars, and star formation rates within each ∼23'' beam. For unresolved galaxies, these physical properties characterize the galaxies' recent star formation on a global scale. We confirm that the radio–far-infrared correlation holds for the unresolved galaxies' total 33 GHz flux regardless of their thermal fractions, though the scatter on this correlation is larger than that at 1.4 GHz. In addition, we found that for the unresolved galaxies, there is an inverse relationship between the ratio of 33 GHz flux to total far-infrared flux and the steepness of the galaxy's spectral index between 1.4 GHz and 33 GHz. This relationship could be an indicator of the timescale of the observed episode of star formation.

We present the first dynamical mass measurements for Lyα galaxies at high redshift, based on velocity dispersion measurements from rest-frame optical emission lines and size measurements from Hubble Space Telescope imaging, for nine galaxies drawn from four surveys. We use these measurements to study Lyα galaxies in the context of galaxy scaling relations. The resulting dynamical masses range from 10⁹ to 10¹⁰ M_☉. We also fit stellar population models to our sample and use them to place the Lyα sample on a stellar mass versus line width relation. The Lyα galaxies generally follow the same scaling relation as star-forming galaxies at lower redshift, although, lower stellar mass fits are also acceptable in ∼1/3 of the Lyα galaxies. Using the dynamical masses as an upper limit on gas mass, we show that Lyα galaxies have unusually active star formation for their gas mass surface density. This behavior is consistent with what is observed in starburst galaxies, despite the typically smaller masses and sizes of the Lyα galaxy population. Finally, we examine the mass densities of these galaxies and show that their future evolution likely requires dissipational ("wet") merging. In short, we find that Lyα galaxies are low-mass cousins of larger starbursts.

The double explosion of SN 2009ip in 2012 raises questions about our understanding of the late stages of massive star evolution. Here we present a comprehensive study of SN 2009ip during its remarkable rebrightenings. High-cadence photometric and spectroscopic observations from the GeV to the radio band obtained from a variety of ground-based and space facilities (including the Very Large Array, Swift, Fermi, Hubble Space Telescope, and XMM) constrain SN 2009ip to be a low energy (E ∼ 10⁵⁰ erg for an ejecta mass ∼0.5 M_☉) and asymmetric explosion in a complex medium shaped by multiple eruptions of the restless progenitor star. Most of the energy is radiated as a result of the shock breaking out through a dense shell of material located at ∼5 × 10¹⁴ cm with M ∼ 0.1 M_☉, ejected by the precursor outburst ∼40 days before the major explosion. We interpret the NIR excess of emission as signature of material located further out, the origin of which has to be connected with documented mass-loss episodes in the previous years. Our modeling predicts bright neutrino emission associated with the shock break-out if the cosmic-ray energy is comparable to the radiated energy. We connect this phenomenology with the explosive ejection of the outer layers of the massive progenitor star, which later interacted with material deposited in the surroundings by previous eruptions. Future observations will reveal if the massive luminous progenitor star survived. Irrespective of whether the explosion was terminal, SN 2009ip brought to light the existence of new channels for sustained episodic mass loss, the physical origin of which has yet to be identified.

When planetesimals begin to grow by coagulation, they first enter an epoch of runaway, during which the biggest bodies grow faster than all the others. The questions of how runaway ends and what comes next have not been answered satisfactorily. We show that runaway is followed by a new stage—the "trans-Hill stage"—that commences when the bodies that dominate viscous stirring ("big bodies") become trans-Hill, i.e., when their Hill velocity matches the random speed of the small bodies they accrete. Subsequently, the small bodies' random speed grows in lockstep with the big bodies' sizes, such that the system remains in the trans-Hill state. Trans-Hill growth is crucial for determining the efficiency of growing big bodies, as well as their growth timescale and size spectrum. Trans-Hill growth has two sub-stages. In the earlier one, which occurs while the stirring bodies remain sufficiently small, the evolution is collisionless, i.e., collisional cooling among all bodies is irrelevant. The efficiency of forming big bodies in this collisionless sub-stage is very low, ∼10α ≪ 1, where α ∼ 0.005(a/AU)⁻¹ is the ratio between the physical size of a body and its Hill radius. Furthermore, the size spectrum is flat (equal mass per size decade, i.e., q = 4). This collisionless trans-Hill solution explains results from previous coagulation simulations for both the Kuiper Belt and the asteroid belt. The second trans-Hill sub-stage commences once the stirring bodies grow big enough (>α⁻¹ × the size of the accreted small bodies). After that time, collisional cooling among small bodies controls the evolution. The efficiency of forming big bodies rises and the size spectrum becomes more top heavy. Trans-Hill growth can terminate in one of two ways, depending on the sizes of the small bodies. First, mutual accretion of big bodies can become significant and conglomeration proceeds until half of the total mass is converted into big bodies. This mode of growth may explain the observed size distributions of small bodies in the solar system and is explored in our subsequent work. Second, if the big bodies' orbits become separated by their Hill radius, oligarchy commences. This mode likely precedes the formation of fully fledged planets.

Independent component analysis (ICA) has recently been shown to be a promising new path in data analysis and de-trending of exoplanetary time series signals. Such approaches do not require or assume any prior or auxiliary knowledge about the data or instrument in order to de-convolve the astrophysical light curve signal from instrument or stellar systematic noise. These methods are often known as "blind-source separation" (BSS) algorithms. Unfortunately, all BSS methods suffer from an amplitude and sign ambiguity of their de-convolved components, which severely limits these methods in low signal-to-noise (S/N) observations where their scalings cannot be determined otherwise. Here we present a novel approach to calibrate ICA using sparse wavelet calibrators. The Amplitude Calibrated Independent Component Analysis (ACICA) allows for the direct retrieval of the independent components' scalings and the robust de-trending of low S/N data. Such an approach gives us an unique and unprecedented insight in the underlying morphology of a data set, which makes this method a powerful tool for exoplanetary data de-trending and signal diagnostics.

Using a sample of 608 Type Ia supernovae from the SDSS-II and BOSS surveys, combined with a sample of foreground galaxies from SDSS-II, we estimate the weak lensing convergence for each supernova line of sight. We find that the correlation between this measurement and the Hubble residuals is consistent with the prediction from lensing (at a significance of 1.7σ). Strong correlations are also found between the residuals and supernova nuisance parameters after a linear correction is applied. When these other correlations are taken into account, the lensing signal is detected at 1.4σ. We show, for the first time, that distance estimates from supernovae can be improved when lensing is incorporated, by including a new parameter in the SALT2 methodology for determining distance moduli. The recovered value of the new parameter is consistent with the lensing prediction. Using cosmic microwave background data from WMAP7, H₀ data from Hubble Space Telescope and Sloan Digital Sky Survey (SDSS) Baryon acoustic oscillations measurements, we find the best-fit value of the new lensing parameter and show that the central values and uncertainties on Ω_m and w are unaffected. The lensing of supernovae, while only seen at marginal significance in this low-redshift sample, will be of vital importance for the next generation of surveys, such as DES and LSST, which will be systematics-dominated.

We present a new technique for forward-modeling self-subtraction of spatially extended emission in observations processed with angular differential imaging (ADI) algorithms. High-contrast direct imaging of circumstellar disks is limited by quasi-static speckle noise, and ADI is commonly used to suppress those speckles. However, the application of ADI can result in self-subtraction of the disk signal due to the disk's finite spatial extent. This signal attenuation varies with radial separation and biases measurements of the disk's surface brightness, thereby compromising inferences regarding the physical processes responsible for the dust distribution. To compensate for this attenuation, we forward model the disk structure and compute the form of the self-subtraction function at each separation. As a proof of concept, we apply our method to 1.6 and 2.2 μm Keck adaptive optics NIRC2 scattered-light observations of the HD 32297 debris disk reduced using a variant of the "locally optimized combination of images" algorithm. We are able to recover disk surface brightness that was otherwise lost to self-subtraction and produce simplified models of the brightness distribution as it appears with and without self-subtraction. From the latter models, we extract radial profiles for the disk's brightness, width, midplane position, and color that are unbiased by self-subtraction. Our analysis of these measurements indicates a break in the brightness profile power law at r ≈ 110 AU and a disk width that increases with separation from the star. We also verify disk curvature that displaces the midplane by up to 30 AU toward the northwest relative to a straight fiducial midplane.

Young stars are known to show variability due to non-steady mass accretion rate from their circumstellar disks. Accretion flares can produce strong energetic irradiation and heating that may affect the disk in the planet formation region, close to the central star. During an extreme accretion outburst in the young star EX Lupi, the prototype of EXor variables, remarkable changes in molecular gas emission from ∼1 AU in the disk have recently been observed. Here, we focus on water vapor and explore how it is affected by variable accretion luminosity in T Tauri stars. We monitored a young highly variable solar-mass star, DR Tau, using simultaneously two high/medium-resolution spectrographs at the European Southern Observatory Very Large Telescope: VISIR at 12.4 μm to observe water lines from the disk and X-shooter covering from 0.3 to 2.5 μm to constrain the stellar accretion. Three epochs spanning timescales from several days to several weeks were obtained. The accretion luminosity was estimated to change within a factor of ∼2 and no change in water emission was detected at a significant level. In comparison with EX Lupi and EXor outbursts, DR Tau suggests that the less long-lived and weaker variability phenomena typical of T Tauri stars may leave water at planet-forming radii in the disk mostly unaffected. We propose that these systems may provide evidence for two processes that act over different timescales: ultraviolet photochemistry in the disk atmosphere (faster) and heating of the deeper disk layers (slower).

A growing fraction of simple stellar population models, in an aim to create more realistic simulations capable of including stochastic variation in their outputs, begin their simulations with a distribution of discrete stars following a power-law function of masses. Careful attention is needed to create a correctly sampled initial mass function (IMF), and here we provide a solid mathematical method, called MASSCLEAN IMF Sampling, for doing so. We use our method to perform 10 million MASSCLEAN Monte Carlo stellar cluster simulations to determine the most massive star in a mass distribution as a function of the total mass of the cluster. We find that a maximum mass range is predicted, not a single maximum mass. This range is (1) dependent on the total mass of the cluster and (2) independent of an upper stellar mass limit, M_limit, for unsaturated clusters and emerges naturally from our IMF sampling method. We then turn our analysis around, starting with our new database of 25 million simulated clusters, to constrain the highest mass star from the observed integrated colors of a sample of 40 low-mass Large Magellanic Cloud stellar clusters of known age and mass. Finally, we present an analytical description of the maximum mass range of the most massive star as a function of the cluster's total mass and present a new M_max–M_cluster relation.

The magnetic flux rope (MFR) is believed to be the underlying magnetic structure of coronal mass ejections (CMEs). However, it remains unclear how an MFR evolves into and forms the multi-component structure of a CME. In this paper, we perform a comprehensive study of an extreme-ultraviolet (EUV) MFR eruption on 2013 May 22 by tracking its morphological evolution, studying its kinematics, and quantifying its thermal property. As EUV brightenings begin, the MFR starts to rise slowly and shows helical threads winding around an axis. Meanwhile, cool filamentary materials descend spirally down to the chromosphere. These features provide direct observational evidence of intrinsically helical structure of the MFR. Through detailed kinematical analysis, we find that the MFR evolution has two distinct phases: a slow rise phase and an impulsive acceleration phase. We attribute the first phase to the magnetic reconnection within the quasi-separatrix layers surrounding the MFR, and the much more energetic second phase to the fast magnetic reconnection underneath the MFR. We suggest that the transition between these two phases is caused by the torus instability. Moreover, we identify that the MFR evolves smoothly into the outer corona and appears as a coherent structure within the white-light CME volume. The MFR in the outer corona was enveloped by bright fronts that originated from plasma pile-up in front of the expanding MFR. The fronts are also associated with the preceding sheath region followed by the outmost MFR-driven shock.

Cygnus X-3 (Cyg X-3) is a remarkable Galactic microquasar (X-ray binary) emitting from radio to γ-ray energies. In this paper, we consider the hadronic model of emission of γ-rays above 100 MeV and their implications. We focus on the joint γ-ray and neutrino production resulting from proton–proton interactions within the binary system. We find that the required proton injection kinetic power, necessary to explain the γ-ray flux observed by AGILE and Fermi-LAT, is L_p ∼ 10³⁸ erg s⁻¹, a value in agreement with the average bolometric luminosity of the hypersoft state (when Cyg X-3 was repeatedly observed to produce transient γ-ray activity). If we assume an increase of the wind density at the superior conjunction, the asymmetric production of γ-rays along the orbit can reproduce the observed modulation. According to observational constraints and our modeling, a maximal flux of high-energy neutrinos would be produced for an initial proton distribution with a power-law index α = 2.4. The predicted neutrino flux is almost two orders of magnitude less than the two-month IceCube sensitivity at ∼1 TeV. If the protons are accelerated up to PeV energies, the predicted neutrino flux for a prolonged "soft X-ray state" would be a factor of about three lower than the one-year IceCube sensitivity at ∼10 TeV. This study shows that, for a prolonged soft state (as observed in 2006) possibly related to γ-ray activity and a hard distribution of injected protons, Cyg X-3 might be close to being detectable by cubic-kilometer neutrino telescopes such as IceCube.

When magnetic energy density is much larger than that of matter, as in pulsar/black hole magnetospheres, the medium becomes force-free and we need relativity to describe it. As in non-relativistic magnetohydrodynamics (MHD), Alfvénic MHD turbulence in the relativistic limit can be described by interactions of counter-traveling wave packets. In this paper, we numerically study strong imbalanced MHD turbulence in such environments. Here, imbalanced turbulence means the waves traveling in one direction (dominant waves) have higher amplitudes than the opposite-traveling waves (sub-dominant waves). We find that (1) spectrum of the dominant waves is steeper than that of sub-dominant waves, (2) the anisotropy of the dominant waves is weaker than that of sub-dominant waves, and (3) the dependence of the ratio of magnetic energy densities of dominant and sub-dominant waves on the ratio of energy injection rates is steeper than quadratic (i.e., $b_+^2/b_-^2 \propto (\epsilon _+/\epsilon _-)^n$ with n > 2). These results are consistent with those obtained for imbalanced non-relativistic Alfvénic turbulence. This corresponds well to the earlier reported similarity of the relativistic and non-relativistic balanced magnetic turbulence.

Detection of the electromagnetic counterparts of gravitational wave (GW) sources is important to unveil the nature of compact binary coalescences. We perform three-dimensional, time-dependent, multi-frequency radiative transfer simulations for radioactively powered emission from the ejecta of black hole (BH)–neutron star (NS) mergers. Depending on the BH to NS mass ratio, spin of the BH, and equations of state of dense matter, BH–NS mergers can eject more material than NS–NS mergers. In such cases, radioactively powered emission from the BH–NS merger ejecta can be more luminous than that from NS–NS mergers. We show that, in spite of the expected larger distances to BH–NS merger events, the observed brightness of BH–NS mergers can be comparable to or even higher than that of NS–NS mergers. We find that, when the tidally disrupted BH–NS merger ejecta are confined to a small solid angle, the emission from BH–NS merger ejecta tends to be bluer than that from NS–NS merger ejecta for a given total luminosity. Thanks to this property, we might be able to distinguish BH–NS merger events from NS–NS merger events by multi-band observations of the radioactively powered emission. In addition to the GW observations, such electromagnetic observations can potentially provide independent information on the progenitors of GW sources and the nature of compact binary coalescences.

Star-forming regions that are visible at 3.6 μm and Hα but not in the u, g, r, i, z bands of the Sloan Digital Sky Survey are measured in five nearby spiral galaxies to find extinctions averaging ∼3.8 mag and stellar masses averaging ∼5 × 10⁴ M_☉. These regions are apparently young star complexes embedded in dark filamentary shock fronts connected with spiral arms. The associated cloud masses are ∼10⁷ M_☉. The conditions required to make such complexes are explored, including gravitational instabilities in spiral-shocked gas and compression of incident clouds. We find that instabilities are too slow for a complete collapse of the observed spiral filaments, but they could lead to star formation in the denser parts. Compression of incident clouds can produce a faster collapse but has difficulty explaining the semi-regular spacing of some regions along the arms. If gravitational instabilities are involved, then the condensations have the local Jeans mass. Also in this case, the near-simultaneous appearance of equally spaced complexes suggests that the dust lanes, and perhaps the arms too, are relatively young.

The stellar populations of galaxies hold vital clues to their formation histories. In this paper we present results based on modeling stacked spectra of early-type galaxies drawn from the Sloan Digital Sky Survey as a function of velocity dispersion, σ, from 90 km s⁻¹ to 300 km s⁻¹. The spectra are of extremely high quality, with typical signal-to-noise ratio of 1000 Å⁻¹, and a wavelength coverage of 4000 Å −8800 Å. Our population synthesis model includes variation in 16 elements from C to Ba, a two-component star formation history, the shift in effective temperature, Δ T_eff, of the stars with respect to a solar metallicity isochrone, and the stellar initial mass function, among other parameters. In our approach we fit the full optical spectra rather than a select number of spectral indices and are able to, for the first time, measure the abundances of the elements V, Cr, Mn, Co, and Ni from the integrated light of distant galaxies. Our main results are as follows: (1) light-weighted stellar ages range from 6–12 Gyr from low to high σ; (2) [Fe/H] varies by less than 0.1 dex across the entire sample; (3) Mg closely tracks O, and both increase from ≈0.0 at low σ to ∼0.25 at high σ; Si and Ti show a shallower rise with σ, and Ca tracks Fe rather than O; (4) the iron peak elements V, Cr, Mn, and Ni track Fe, while Co tracks O, suggesting that Co forms primarily in massive stars; (5) C and N track O over the full sample and [C/Fe] and [N/Fe] exceed 0.2 at high σ; and (6) the variation in Δ T_eff with total metallicity closely follows theoretical predictions based on stellar evolution theory. This last result is significant because it implies that we are robustly solving not only for the detailed abundance patterns but also the detailed temperature distributions (i.e., isochrones) of the stars in these galaxies. A variety of tests reveal that the systematic uncertainties in our measurements are probably 0.05 dex or less. Our derived [Mg/Fe] and [O/Fe] abundance ratios are 0.05–0.1 dex lower than most previous determinations. Under the conventional interpretation that the variation in these ratios is due to star formation timescale variations, our results suggest longer star formation timescales for massive early-type galaxies than previous studies. Detailed chemical evolution models are necessary in order to translate the abundance ratio distributions of these galaxies into constraints on their formation histories. Alternatively, these data may provide useful constraints on the nucleosynthetic pathways for elements whose production is not well understood.

We present an analysis of an H₁₆₀-selected photometric catalog of galaxies in the Hubble Ultra-Deep Field, using imaging from the WFC3/IR camera on the Hubble Space Telescope in combination with archival ultraviolet, optical, and near-infrared imaging. Using these data, we measure the spectral energy distributions of ∼1500 galaxies to a limiting H₁₆₀ magnitude of 27.8, from which we fit photometric redshifts and stellar population estimates for all galaxies with well-determined Spitzer IRAC fluxes, allowing for the determination of the cumulative mass function within the range 1 < z < 6. By selecting samples of galaxies at a constant cumulative number density, we are able to explore the coevolution of stellar masses and star formation rates (SFRs) for progenitor galaxies and their descendants from z ∼ 6. We find a steady increase in the SFRs of galaxies at constant number density from z ∼ 6 to z ∼ 3, accompanied by gradually declining specific star formation rates (sSFRs) during this same period. The peak epoch of star formation is also found to shift to later times for galaxies with increasing number densities, in agreement with the expectations from cosmic downsizing. The observed SFRs can fully account for the mass growth to z ∼ 2 among galaxies with cumulative number densities greater than 10^−3.5 Mpc⁻³. For galaxies with a lower constant number density (higher mean mass), we find the observed stellar masses are ∼three times greater than that which may be accounted for by the observed star formation alone at late times, implying that growth from mergers plays an important role at z < 2. We additionally observe a decreasing sSFR, equivalent to approximately one order of magnitude, from z ∼ 6 to z ∼ 2 among galaxies with number densities less than 10^−3.5 Mpc⁻³, along with significant evidence that at any redshift the sSFR is higher for galaxies at higher number density. The combination of these findings can qualitatively explain the previous findings of a specific star formation rate plateau at high redshift. Tracing the evolution of the fraction of quiescent galaxies for samples matched in cumulative number density over this redshift range, we find no unambiguous examples of quiescent galaxies at z > 4.

Mrk 766, a bright narrow-line Seyfert 1, has been observed eight times by the XMM-Newton satellite. We carried out the analysis of the composite data from all of these observations together by applying a dynamical method. Through this analysis, we noted a longer timescale variability in addition to rapid short-time variability. This longer term variability is manifested by the presence of two distinct branches in flux–flux plots. Moreover, the data show the presence of absorbing material whose average thickness decreases gradually from ∼2 × 10²³ cm⁻² during the dim state to ∼10²² cm⁻² as the source brightens to brighter states. To explain this longer timescale behavior and others already found self-consistently, we offer a promising model. In this model, the source is dim when a small emission region is covered by a small, denser portion of a partial-covering cloud; the source brightens as it becomes larger and covered predominantly by a less dense, larger region of the covering cloud. The short rapid variability, in contrast, is consistent with the highly variable power-law component from the coronal primary emission region, which is superimposed onto a less variable, ionized relativistic reflection component. Last, a possible presence of some unique soft flares is suggested. Unlike many other flares seen in the light curves, these flares occur only in the 0.3–2.0 keV soft band. These soft flares may be attributed to "hot spots" on the accretion disk.

We present new large field observations of molecular clouds with NANTEN2 toward the super star cluster NGC 3603 in the transitions ¹²CO(J = 2–1, J = 1–0) and ¹³CO(J = 2–1, J = 1–0). We suggest that two molecular clouds at 13 km s⁻¹ and 28 km s⁻¹ are associated with NGC 3603 as evidenced by higher temperatures toward the H ii region, as well as morphological correspondence. The mass of the clouds is too small to gravitationally bind them, given their relative motion of ∼20 km s⁻¹. We suggest that the two clouds collided with each other 1 Myr ago to trigger the formation of the super star cluster. This scenario is able to explain the origin of the highest mass stellar population in the cluster, which is as young as 1 Myr and is segregated within the central sub-pc of the cluster. This is the second super star cluster along with Westerlund 2 where formation may have been triggered by a cloud–cloud collision.

Past analyses of Type Ia supernovae have identified an irreducible scatter of 5%–10% in distance, widely attributed to an intrinsic dispersion in luminosity. Another equally valid source of this scatter is intrinsic dispersion in color. Misidentification of the true source of this scatter can bias both the retrieved color–luminosity relation and cosmological parameter measurements. The size of this bias depends on the magnitude of the intrinsic color dispersion relative to the distribution of colors that correlate with distance. We produce a realistic simulation of a misattribution of intrinsic scatter and find a negative bias in the recovered color–luminosity relation, β, of Δβ ≈ −1.0 (∼33%) and a positive bias in the equation of state parameter, w, of Δw ≈ +0.04 (∼4%). We re-analyze current published datasets with the assumption that the distance scatter is predominantly the result of color. Unlike previous analyses, we find that the data are consistent with a Milky-Way-like reddening law (R_V = 3.1) and that a Milky-Way dust model better predicts the asymmetric color–luminosity trends than the conventional luminosity scatter hypothesis. We also determine that accounting for color variation reduces the correlation between various host galaxy properties and Hubble residuals by ∼20%.

We develop a Monte Carlo Comptonization model for the X-ray spectrum of accretion-powered pulsars. Simple, spherical, thermal Comptonization models give harder spectra for higher optical depth, while the observational data from Vela X-1 show that the spectra are harder at higher luminosity. This suggests a physical interpretation where the optical depth of the accreting plasma increases with the mass accretion rate. We develop a detailed Monte Carlo model of the accretion flow, including the effects of the strong magnetic field (∼10¹² G), both in geometrically constraining the flow into an accretion column and in reducing the cross section. We treat bulk-motion Comptonization of the infalling material as well as thermal Comptonization. These model spectra can match the observed broadband Suzaku data from Vela X-1 over a wide range of mass accretion rates. The model can also explain the so-called "low state" in which the luminosity decreases by an order of magnitude. Here, thermal Comptonization should be negligible, so the spectrum is instead dominated by bulk-motion Comptonization.

We analyze 18 sources that showed interesting properties of periodicity, very soft spectra, and/or large long-term variability in X-rays in our project of classification of sources from the 2XMMi-DR3 catalog, but were poorly studied in the literature, in order to investigate their nature. Two hard sources show X-ray periodicities of ∼1.62 hr (2XMM J165334.4−414423) and ∼2.1 hr (2XMM J133135.2−315541) and are probably magnetic cataclysmic variables. One source, 2XMM J123103.2+110648, is an active galactic nucleus (AGN) candidate showing very soft X-ray spectra (kT ∼ 0.1 keV) and exhibiting an intermittent ∼3.8 hr quasi-periodic oscillation. There are six other very soft sources (with kT < 0.2 keV), which might be in other galaxies with luminosities between ∼10³⁸–10⁴² erg s⁻¹. They probably represent a diverse group that might include objects such as ultrasoft AGNs and cool thermal disk emission from accreting intermediate-mass black holes. Six highly variable sources with harder spectra are probably in nearby galaxies with luminosities above 10³⁷ erg s⁻¹ and thus are great candidates for extragalactic X-ray binaries. One of them (2XMMi J004211.2+410429, in M31) is probably a new-born persistent source, having been X-ray bright and hard in 0.3–10 keV for at least four years since it was discovered entering an outburst in 2007. Three highly variable hard sources appear at low galactic latitudes and have maximum luminosities below ∼10³⁴ erg s⁻¹ if they are in our Galaxy. Thus, they are great candidates for cataclysmic variables or very faint X-ray transients harboring a black hole or neutron star. Our interpretations of these sources can be tested with future long-term X-ray monitoring and multi-wavelength observations.

We model molecular cloud fragmentation with thin-disk, non-ideal magnetohydrodynamic simulations that include ambipolar diffusion and partial ionization that transitions from primarily ultraviolet-dominated to cosmic-ray-dominated regimes. These simulations are used to determine the conditions required for star clusters to form through a two-stage fragmentation scenario. Recent linear analyses have shown that the fragmentation length scales and timescales can undergo a dramatic drop across the column density boundary that separates the ultraviolet- and cosmic-ray-dominated ionization regimes. As found in earlier studies, the absence of an ionization drop and regular perturbations leads to a single-stage fragmentation on pc scales in transcritical clouds, so that the nonlinear evolution yields the same fragment sizes as predicted by linear theory. However, we find that a combination of initial transcritical mass-to-flux ratio, evolution through a column density regime in which the ionization drop takes place, and regular small perturbations to the mass-to-flux ratio is sufficient to cause a second stage of fragmentation during the nonlinear evolution. Cores of size ∼0.1 pc are formed within an initial fragment of ∼pc size. Regular perturbations to the mass-to-flux ratio also accelerate the onset of runaway collapse.

We present a detailed analysis of the mid-infrared spectrum of the peculiar evolved object HR 4049. The full Spitzer-IRS high-resolution spectrum shows a wealth of emission with prominent features from CO₂ and H₂O and possible contributions from HCN and OH. We model the molecular emission and find that it originates from a massive (M ≳ 8 × 10⁻³M_☉), warm (T_ex ≈ 500 K) and radially extended gas disk that is optically thick at infrared wavelengths. We also report less enrichment in ¹⁷O and ¹⁸O than previously found and a comparison of the Spitzer observations to earlier data obtained by the Short Wavelength Spectrometer on board the Infrared Space Observatory reveals that the CO₂ flux has more than doubled in 10 yr time, indicating active and ongoing chemical evolution in the circumbinary disk. If the gas originates from interaction between the stellar wind and the dust, this suggests that the dust could be oxygen-rich in nature. The molecular gas plays a crucial role in the thermal properties of the circumbinary disk by allowing visible light to heat the dust and then trapping the infrared photons emitted by the dust. This results in higher temperatures and a more homogeneous temperature structure in the disk.

Young stars with masses 2–8 times solar, the Herbig Ae and Be stars, often show a near-infrared excess too large to explain with a hydrostatically supported circumstellar disk of gas and dust. At the same time, the accretion flow carrying the circumstellar gas to the star is thought to be driven by magnetorotational turbulence, which, according to numerical MHD modeling, yields an extended low-density atmosphere supported by the magnetic fields. We demonstrate that the base of the atmosphere can be optically thick to the starlight and that the parts lying near 1 AU are tall enough to double the fraction of the stellar luminosity reprocessed into the near-infrared. We generate synthetic spectral energy distributions (SEDs) using Monte Carlo radiative transfer calculations with opacities for submicron silicate and carbonaceous grains. The synthetic SEDs closely follow the median Herbig SED constructed recently by Mulders & Dominik and, in particular, match the large near-infrared flux, provided the grains have a mass fraction close to interstellar near the disk's inner rim.

Several recent studies have provided evidence for a "bottom-heavy" stellar initial mass function (IMF) in massive elliptical galaxies. Here we investigate the influence of the IMF shape on the recently discovered color–magnitude relation (CMR) among globular clusters (GCs) in such galaxies. To this end we use calculations of GC mass loss due to stellar and dynamical evolution to evaluate (1) the shapes of stellar mass functions in GCs after 12 Gyr of evolution as a function of current GC mass along with their effects on integrated-light colors and mass-to-light ratios, and (2) their impact on the effects of GC self-enrichment using the 2009 "reference" model of Bailin & Harris. As to the class of metal-poor GCs, we find the observed shape of the CMR (often referred to as the "blue tilt") to be very well reproduced by Bailin & Harris's reference self-enrichment model once 12 Gyr of GC mass loss is taken into account. The influence of the IMF on this result is found to be insignificant. However, we find that the observed CMR among the class of metal-rich GCs (the "red tilt") can only be adequately reproduced if the IMF was bottom-heavy (−3.0 ≲ α ≲ −2.3 in $dN/d{\cal {M}}\propto {\cal {M}}^{\alpha }$), which causes the stellar mass function at subsolar masses to depend relatively strongly on GC mass. This constitutes additional evidence that the metal-rich stellar populations in giant elliptical galaxies were formed with a bottom-heavy IMF.

We present the Pan-STARRS1 discovery of the long-lived and blue transient PS1-11af, which was also detected by Galaxy Evolution Explorer with coordinated observations in the near-ultraviolet (NUV) band. PS1-11af is associated with the nucleus of an early type galaxy at redshift z = 0.4046 that exhibits no evidence for star formation or active galactic nucleus activity. Four epochs of spectroscopy reveal a pair of transient broad absorption features in the UV on otherwise featureless spectra. Despite the superficial similarity of these features to P-Cygni absorptions of supernovae (SNe), we conclude that PS1-11af is not consistent with the properties of known types of SNe. Blackbody fits to the spectral energy distribution are inconsistent with the cooling, expanding ejecta of a SN, and the velocities of the absorption features are too high to represent material in homologous expansion near a SN photosphere. However, the constant blue colors and slow evolution of the luminosity are similar to previous optically selected tidal disruption events (TDEs). The shape of the optical light curve is consistent with models for TDEs, but the minimum accreted mass necessary to power the observed luminosity is only ∼0.002 M_☉, which points to a partial disruption model. A full disruption model predicts higher bolometric luminosities, which would require most of the radiation to be emitted in a separate component at high energies where we lack observations. In addition, the observed temperature is lower than that predicted by pure accretion disk models for TDEs and requires reprocessing to a constant, lower temperature. Three deep non-detections in the radio with the Very Large Array over the first two years after the event set strict limits on the production of any relativistic outflow comparable to Swift J1644+57, even if off-axis.

We present a comparison of two Suzaku X-ray observations of the nearby (z = 0.184), luminous (L_bol ∼ 10⁴⁷ erg s⁻¹) type I quasar, PDS 456. A new 125 ks Suzaku observation in 2011 caught the quasar during a period of low X-ray flux and with a hard X-ray spectrum, in contrast with a previous 190 ks Suzaku observation in 2007 when the quasar appeared brighter and had a steep (Γ > 2) X-ray spectrum. The 2011 X-ray spectrum contains a pronounced trough near 9 keV in the quasar rest frame, which can be modeled with blueshifted iron K-shell absorption, most likely from the He- and H-like transitions of iron. The absorption trough is observed at a similar rest-frame energy as in the earlier 2007 observation, which appears to confirm the existence of a persistent high-velocity wind in PDS 456, at an outflow velocity of 0.25–0.30c. The spectral variability between 2007 and 2011 can be accounted for by variations in a partial covering absorber, increasing in covering fraction from the brighter 2007 observation to the hard and faint 2011 observation. Overall, the low-flux 2011 observation can be explained if PDS 456 is observed at relatively low inclination angles through a Compton-thick wind, originating from the accretion disk, which significantly attenuates the X-ray flux from the quasar.

We investigate the formation of hot coronae and vertical outflows in accretion disks by magnetorotational turbulence. We perform local three-dimensional magnetohydrodynamical (MHD) simulations with the vertical stratification by explicitly solving an energy equation with various effective ratios of specific heats, γ. Initially imposed weak vertical magnetic fields are effectively amplified by magnetorotational instability and winding caused by the differential rotation. In the isothermal case (γ = 1), the disk winds are driven mainly by the Poynting flux associated with the MHD turbulence and show quasi-periodic intermittency. In contrast, in the non-isothermal cases with γ ⩾ 1.1, the regions above 1–2 scale heights from the midplane are effectively heated to form coronae with temperature ∼50 times the initial value, which are connected to the cooler midplane region through the pressure-balanced transition regions. As a result, the disk winds are driven mainly by the gas pressure, exhibiting more time-steady nature, although the nondimensional time-averaged mass loss rates are similar to that of the isothermal case. Sound-like waves are confined in the cool midplane region in these cases, and the amplitude of the density fluctuations is larger than that of the isothermal case.

SMC X-1 is a high-mass X-ray binary with an orbital period of 3.9 days. The mass of the neutron star is as low as ∼1M_☉, suggesting that it was likely formed through an electron-capture supernova rather than an iron-core collapse supernova. From the present system configurations, we argue that the orbital period at the supernova was ≲ 10 days. Since the mass transfer process between the neutron star's progenitor and the companion star before the supernova should have increased the orbital period to tens of days, a mechanism with efficient orbit angular momentum loss and relatively small mass loss is required to account for its current orbital period. We have calculated the evolution of the progenitor binary systems from zero-age main sequence to the pre-supernova stage with different initial parameters and various mass and angular momentum loss mechanisms. Our results show that the outflow from the outer Lagrangian point or a circumbinary disk formed during the mass transfer phase may be qualified for this purpose. We point out that these mechanisms may be popular in binary evolution and significantly affect the formation of compact star binaries.

We present contemporaneous X-ray, ultraviolet (UV), optical, and near-infrared observations of the black hole binary system Swift J1753.5−0127 acquired in 2012 October. The UV observations, obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope, are the first UV spectra of this system. The dereddened UV spectrum is characterized by a smooth, blue continuum and broad emission lines of C iv and He ii. The system was stable in the UV to <10% during our observations. We estimated the interstellar reddening by fitting the 2175 Å absorption feature and fit the interstellar absorption profile of Lyα to directly measure the neutral hydrogen column density along the line of sight. By comparing the UV continuum flux to steady-state thin accretion disk models, we determined upper limits on the distance to the system as a function of black hole mass. The continuum is well fit with disk models dominated by viscous heating rather than irradiation. The broadband spectral energy distribution shows the system has declined at all wavelengths since previous broadband observations in 2005 and 2007. If we assume that the UV emission is dominated by the accretion disk, the inner radius of the disk must be truncated at radii above the innermost stable circular orbit to be consistent with the X-ray flux, requiring significant mass loss from outflows and/or energy loss via advection into the black hole to maintain energy balance.

The molecular outflow from IRAS 04166+2706 was mapped with the Submillimeter Array at a 350 GHz continuum and CO J = 3–2 at an angular resolution of ∼1''. The field of view covers the central arcminute, which contains the inner four pairs of knots of the molecular jet. On the channel map, conical structures are clearly present in the low-velocity range (|V − V₀| < 10 km s⁻¹), and the highly collimated knots appear in the extremely high velocity range (50 >|V − V₀| > 30 km s⁻¹). The higher angular resolution of ∼1'' reveals the first blue-shifted knot (B1) that was missing in previous Plateau de Bure Interferometer observation of Santiago-García et al. at an offset of ∼6'' to the northeast of the central source. This identification completes the symmetric sequence of knots in both the blue- and red-shifted lobes of the outflow. The innermost knots R1 and B1 have the highest velocities within the sequence. Although the general features appear to be similar to previous CO J = 2–1 images in Santiago-García et al., the emission in CO J = 3–2 almost always peaks further away from the central source than that of CO J = 2–1 in the red-shifted lobe of the channel maps. This gives rise to a gradient in the line-ratio map of CO J = 3–2/J = 2–1 from head to tail within a knot. A large velocity gradient analysis suggests that the differences may reflect a higher gas kinetic temperature at the head. We also explore possible constraints imposed by the nondetection of SiO J = 8–7.

We present a study of the plerionic supernova remnant 0540-69.3 in the LMC in X-ray, radio, optical, and infrared. We find that the shell of 0540-69.3 is characterized in the X-ray by thermal nonequilibrium plasma with depleted Mg and Si abundances and a temperature of kT ∼ 0.7 keV. This thermal emission is superimposed with synchrotron emission in several regions. Based on X-ray spectra and on morphological considerations in all surveyed wavebands, we conclude that the shell is expanding into a clumpy and highly inhomogeneous medium. In one region of the shell we find an overabundance of Ne, suggesting the presence of ejecta near the edge of the remnant. We also see evidence for reheating of material via a reverse shock originating from the interaction of the supernova blast wave with a particularly dense cloud in the surrounding medium. Finally, we perform the first detailed study of the "halo" region extending 1.2–2.2 pc from the central pulsar. We detect the presence of thermal and nonthermal spectral components but do not find evidence for mixing or ejecta. We conclude that the thermal component is not a counterpart to similar optical and infrared halos and that it is most likely due to the projection of shell material along the line of sight.

We report on the first phase of a study of cloud irradiation. We study irradiation by means of numerical, two-dimensional, time-dependent radiation hydrodynamic simulations of a strongly irradiated cloud. We adopt a very simple treatment of the opacity, neglect photoionization and gravity, and focus instead on assessing the role of the type and magnitude of the opacity on the cloud evolution. Our main result is that even relatively dense clouds that are radiatively heated (i.e., with significant absorption opacity) do not move as a whole; instead, they undergo very rapid and major evolution in shape, size, and physical properties. In particular, the cloud and its remnants become optically thin in less than 1 sound-crossing time and before they can travel a significant distance (a few initial-cloud radii). We also find that a cloud can be accelerated as a whole under quite extreme conditions, i.e., the opacity must be dominated by scattering. However, the acceleration due to the radiation force is relatively small, and unless the cloud is optically thin, it quickly undergoes changes in size and shape. We discuss implications for the modeling and interpretation of the broad-line regions of active galactic nuclei.

Ongoing searches for exoplanetary systems have revealed a wealth of planets with diverse physical properties. Planets even smaller than the Earth have already been detected and the efforts of future missions are aimed at the discovery, and perhaps characterization, of small rocky exoplanets within the habitable zone of their stars. Clearly, what we know about our planet will be our guideline for the characterization of such planets. However, the Earth has been inhabited for at least 3.8 Gyr and its appearance has changed with time. Here, we have studied the Earth during the Archean eon, 3.0 Gyr ago. At that time, one of the more widespread life forms on the planet was purple bacteria. These bacteria are photosynthetic microorganisms and can inhabit both aquatic and terrestrial environments. Here, we use a radiative transfer model to simulate the visible and near-infrared radiation reflected by our planet, taking into account several scenarios regarding the possible distribution of purple bacteria over continents and oceans. We find that purple bacteria have a reflectance spectrum that has a strong reflectivity increase, similar to the red edge of leafy plants, although shifted redward. This feature produces a detectable signal in the disk-averaged spectra of our planet, depending on cloud amount and purple bacteria concentration/distribution. We conclude that by using multi-color photometric observations, it is possible to distinguish between an Archean Earth in which purple bacteria inhabit vast extensions of the planet and a present-day Earth with continents covered by deserts, vegetation, or microbial mats.

The compact multi-transiting planet systems discovered by Kepler challenge planet formation theories. Formation in situ from disks with radial mass surface density, Σ, profiles similar to the minimum mass solar nebula but boosted in normalization by factors ≳ 10 has been suggested. We propose that a more natural way to create these planets in the inner disk is formation sequentially from the inside-out via creation of successive gravitationally unstable rings fed from a continuous stream of small (∼cm–m size) "pebbles," drifting inward via gas drag. Pebbles collect at the pressure maximum associated with the transition from a magnetorotational instability (MRI)-inactive ("dead zone") region to an inner MRI-active zone. A pebble ring builds up until it either becomes gravitationally unstable to form an ∼1 M_⊕ planet directly or induces gradual planet formation via core accretion. The planet may undergo Type I migration into the active region, allowing a new pebble ring and planet to form behind it. Alternatively, if migration is inefficient, the planet may continue to accrete from the disk until it becomes massive enough to isolate itself from the accretion flow. A variety of densities may result depending on the relative importance of residual gas accretion as the planet approaches its isolation mass. The process can repeat with a new pebble ring gathering at the new pressure maximum associated with the retreating dead-zone boundary. Our simple analytical model for this scenario of inside-out planet formation yields planetary masses, relative mass scalings with orbital radius, and minimum orbital separations consistent with those seen by Kepler. It provides an explanation of how massive planets can form with tightly packed and well-aligned system architectures, starting from typical protoplanetary disk properties.

We used Keck adaptive optics observations to identify the first planet discovered by microlensing to lie in or near the habitable zone, i.e., at projected separation r_⊥ = 1.1 ± 0.1 AU from its M_L = 0.86 ± 0.06 M_☉ host, being the highest microlensing mass definitely identified. The planet has a mass m_p = 4.8 ± 0.3 M_Jup, and could in principle have habitable moons. This is also the first planet to be identified as being in the Galactic bulge with good confidence: D_L = 7.72 ± 0.44 kpc. The planet/host masses and distance were previously not known, but only estimated using Bayesian priors based on a Galactic model. These estimates had suggested that the planet might be a super-Jupiter orbiting an M dwarf, a very rare class of planets. We obtained high-resolution JHK images using Keck adaptive optics to detect the lens and so test this hypothesis. We clearly detect light from a G dwarf at the position of the event, and exclude all interpretations other than that this is the lens with high confidence (95%), using a new astrometric technique. The calibrated magnitude of the planet host star is H_L = 19.16 ± 0.13. We infer the following probabilities for the three possible orbital configurations of the gas giant planet: 53% to be in the habitable zone, 35% to be near the habitable zone, and 12% to be beyond the snow line, depending on the atmospherical conditions and the uncertainties on the semimajor axis.

We present a comprehensive study of the formation and eruption of an active region (AR) sigmoid in AR 11283. To follow the quasi-static evolution of the coronal magnetic field, we reconstruct a time sequence of static fields using a recently developed nonlinear force-free field model constrained by vector magnetograms. A detailed analysis of the fields compared with observations suggests the following scenario for the evolution of the region. Initially, a new bipole emerges into the negative polarity of a preexisting bipolar AR, forming a null-point topology between the two flux systems. A weakly twisted flux rope (FR) is then built up slowly in the embedded core region, largely through flux cancellation, forming a bald patch separatrix surface (BPSS). The FR grows gradually until its axis runs into a torus instability (TI) domain, and the BPSS also develops a full S-shape. The combined effects of the TI-driven expansion of the FR and the line tying at the BP tear the FR into two parts with the upper portion freely expelled and the lower portion remaining behind the postflare arcades. This process dynamically perturbs the BPSS and results in the enhanced heating of the sigmoid and the rope. The accelerated expansion of the upper-portion rope strongly pushes its envelope flux near the null point and triggers breakout reconnection at the null, which further drives the eruption. We discuss the important implications of these results for the formation and disruption of the sigmoid region with an FR.

The parametric instabilities of an Alfvén wave in a proton–electron plasma system are found to have great influence on proton dynamics, where part of the protons can be accelerated through the Landau resonance with the excited ion acoustic waves, and a beam component along the background magnetic field is formed. In this paper, with a one-dimensional hybrid simulation model, we investigate the evolution of the parametric instabilities of a monochromatic left-hand polarized Alfvén wave in a proton–electron–alpha plasma with a low beta. When the drift velocity between the protons and alpha particles is sufficiently large, the wave numbers of the backward daughter Alfvén waves can be cascaded toward higher values due to the modulational instability during the nonlinear evolution of the parametric instabilities, and the alpha particles are resonantly heated in both the parallel and perpendicular direction by the backward waves. On the other hand, when the drift velocity of alpha particles is small, the alpha particles are heated in the linear growth stage of the parametric instabilities due to the Landau resonance with the excited ion acoustic waves. Therefore, the heating occurs only in the parallel direction, and there is no obvious heating in the perpendicular direction. The relevance of our results to the preferential heating of heavy ions observed in the solar wind within 0.3 AU is also discussed in this paper.

Star-forming disk galaxies at high redshift are often subject to violent disk instability, characterized by giant clumps whose fate is yet to be understood. The main question is whether the clumps disrupt within their dynamical timescale (⩽50 Myr), like the molecular clouds in today's galaxies, or whether they survive stellar feedback for more than a disk orbital time (≈300 Myr) in which case they can migrate inward and help building the central bulge. We present 3.5–7 pc resolution adaptive mesh refinement simulations of high-redshift disks including photoionization, radiation pressure, and supernovae feedback. Our modeling of radiation pressure determines the mass loading and initial velocity of winds from basic physical principles. We find that the giant clumps produce steady outflow rates comparable to and sometimes somewhat larger than their star formation rate, with velocities largely sufficient to escape the galaxy. The clumps also lose mass, especially old stars, by tidal stripping, and the stellar populations contained in the clumps hence remain relatively young (⩽200 Myr), as observed. The clumps survive gaseous outflows and stellar loss, because they are wandering in gas-rich turbulent disks from which they can reaccrete gas at high rates compensating for outflows and tidal stripping, overall keeping realistic and self-regulated gaseous and stellar masses. The outflow and accretion rates have specific timescales of a few 10⁸ yr, as opposed to rapid and repeated dispersion and reformation of clumps. Our simulations produce gaseous outflows with velocities, densities, and mass loading consistent with observations, and at the same time suggest that the giant clumps survive for hundreds of Myr and complete their migration to the center of high-redshift galaxies. These long-lived clumps are gas-dominated and contain a moderate mass fraction of stars; they drive inside-out disk evolution, thickening, spheroid growth, and fueling of the central black hole.

We previously identified LH146, a diffuse X-ray source in the Lockman Hole, as a galaxy cluster at redshift 1.753. The redshift was based on one spectroscopic value, buttressed by seven additional photometric redshifts. We confirm here the previous spectroscopic redshift and present concordant spectroscopic redshifts for an additional eight galaxies. The average of these nine redshifts is 1.714 ± 0.012 (error on the mean). Scrutiny of the galaxy distribution in redshift space and the plane of the sky shows that there are two concentrations of galaxies near the X-ray source. In addition, there are three diffuse X-ray sources spread along the axis connecting the galaxy concentrations. LH146 is one of these three and lies approximately at the center of the two galaxy concentrations and the outer two diffuse X-ray sources. We thus conclude that LH146 is at the redshift initially reported but it is not a single virialized galaxy cluster, as previously assumed. Rather, it appears to mark the approximate center of a larger region containing more objects. For brevity, we refer to all these objects and their alignments as a large-scale structure. The exact nature of LH146 itself remains unclear.

We present a distance determination to the Small Magellanic Cloud (SMC) based on an analysis of four detached, long-period, late-type eclipsing binaries discovered by the Optical Gravitational Lensing Experiment (OGLE) survey. The components of the binaries show negligible intrinsic variability. A consistent set of stellar parameters was derived with low statistical and systematic uncertainty. The absolute dimensions of the stars are calculated with a precision of better than 3%. The surface brightness–infrared color relation was used to derive the distance to each binary. The four systems clump around a distance modulus of (m − M) = 18.99 with a dispersion of only 0.05 mag. Combining these results with the distance published by Graczyk et al. for the eclipsing binary OGLE SMC113.3 4007, we obtain a mean distance modulus to the SMC of 18.965 ± 0.025 (stat.) ± 0.048 (syst.) mag. This corresponds to a distance of 62.1 ± 1.9 kpc, where the error includes both uncertainties. Taking into account other recent published determinations of the SMC distance we calculated the distance modulus difference between the SMC and the Large Magellanic Cloud equal to 0.458 ± 0.068 mag. Finally, we advocate μ_SMC = 18.95 ± 0.07 as a new "canonical" value of the distance modulus to this galaxy.

We propose and analyze a new mechanism for the formation of the wide asynchronous binary population. These binary asteroids have wide semimajor axes relative to most near-Earth and main belt asteroid systems. Confirmed members have rapidly rotating primaries and satellites that are not tidally locked. Previously suggested formation mechanisms from impact ejecta, from planetary flybys, and directly from rotational fission events cannot satisfy all of the observations. The newly hypothesized mechanism works as follows: (1) these systems are formed from rotational fission, (2) their satellites are tidally locked, (3) their orbits are expanded by the binary Yarkovsky–O'Keefe–Radzievskii–Paddack (BYORP) effect, (4) their satellites desynchronize as a result of the adiabatic invariance between the libration of the secondary and the mutual orbit, and (5) the secondary avoids resynchronization because of the YORP effect. This seemingly complex chain of events is a natural pathway for binaries with satellites that have particular shapes, which define the BYORP effect torque that acts on the system. After detailing the theory, we analyze each of the wide asynchronous binary members and candidates to assess their most likely formation mechanism. Finally, we suggest possible future observations to check and constrain our hypothesis.

Extreme ultraviolet (EUV) radiations (10–117 nm) from host stars play important roles in the ionization, heating, and mass loss from exoplanet atmospheres. Together with the host star's Lyα and far-UV (117–170 nm) radiation, EUV radiation photodissociates important molecules, thereby changing the chemistry in exoplanet atmospheres. Since stellar EUV fluxes cannot now be measured and interstellar neutral hydrogen completely obscures stellar radiation between 40 and 91.2 nm, even for the nearest stars, we must estimate the unobservable EUV flux by indirect methods. New non-LTE semiempirical models of the solar chromosphere and corona and solar irradiance measurements show that the ratio of EUV flux in a variety of wavelength bands to the Lyα flux varies slowly with the Lyα flux and thus with the magnetic heating rate. This suggests and we confirm that solar EUV/Lyα flux ratios based on the models and observations are similar to the available 10–40 nm flux ratios observed with the Extreme Ultraviolet Explorer (EUVE) satellite and the 91.2–117 nm flux observed with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite for F5 V–M5 V stars. We provide formulae for predicting EUV flux ratios based on the EUVE and FUSE stellar data and on the solar models, which are essential input for modeling the atmospheres of exoplanets.

We present 0.9–2.5 μm resolved spectra for the ultracool binary WISEPC J121756.91+162640.2AB. The system consists of a pair of brown dwarfs that straddles the currently defined T/Y spectral type boundary. We use synthetic spectra generated by model atmospheres that include chloride and sulfide clouds (Morley et al.), the distance to the system (Dupuy & Kraus), and the radius of each component based on evolutionary models (Saumon & Marley) to determine a probable range of physical properties for the binary. The effective temperature of the T8.5 primary is 550–600 K and that of the Y0–Y0.5 secondary is ≈450 K. The atmospheres of both components are either free of clouds or have extremely thin cloud layers. We find that the masses of the primary and secondary are 30 and 22 M_Jup, respectively, and that the age of the system is 4–8 Gyr. This age is consistent with astrometric measurements (Dupuy & Kraus) that show that the system has kinematics intermediate between those of the thin and thick disks of the Galaxy. An older age is also consistent with an indication by the H − K colors that the system is slightly metal poor.

The microquasar 1E1740.7-2942, also known as the "Great Annihilator," was observed by NuSTAR in the summer of 2012. We have analyzed in detail two observations taken ∼2 weeks apart, for which we measure hard and smooth spectra typical of the low/hard state. A few weeks later the source flux declined significantly. Nearly simultaneous coverage by INTEGRAL is available from its Galactic Center monitoring campaign lasting ∼2.5 months. These data probe the hard state spectrum from 1E1740.7-2942 before the flux decline. We find good agreement between the spectra taken with IBIS/ISGRI and NuSTAR, with the measurements being compatible with a change in flux with no spectral variability. We present a detailed analysis of the NuSTAR spectral and timing data and upper limits for reflection of the high energy emission. We show that the high energy spectrum of this X-ray binary is well described by thermal Comptonization.

The second-order Fermi acceleration (Fermi-II) driven by turbulence may be responsible for the electron acceleration in blazar jets. We test this model with time-dependent simulations. The hard electron spectrum predicted by the Fermi-II process agrees with the hard photon spectrum of 1ES 1101−232. For other blazars that show softer spectra, the Fermi-II model requires radial evolution of the electron injection rate and/or diffusion coefficient in the outflow. Such evolutions can yield a curved electron spectrum, which can reproduce the synchrotron spectrum of Mrk 421 from the radio to the X-ray regime. The photon spectrum in the GeV energy range of Mrk 421 is hard to fit with a synchrotron self-Compton model. However, if we introduce an external radio photon field with a luminosity of 4.9 × 10³⁸ erg s⁻¹, GeV photons are successfully produced via inverse Compton scattering. The temporal variability of the diffusion coefficient or injection rate causes flare emission. The observed synchronicity of X-ray and TeV flares implies a decrease of the magnetic field in the flaring source region.

Planets can affect debris disk structure by creating gaps, sharp edges, warps, and other potentially observable signatures. However, there is currently no simple way for observers to deduce a disk-shepherding planet's properties from the observed features of the disk. Here we present a single equation that relates a shepherding planet's maximum mass to the debris ring's observed width in scattered light, along with a procedure to estimate the planet's eccentricity and minimum semimajor axis. We accomplish this by performing dynamical N-body simulations of model systems containing a star, a single planet, and an exterior disk of parent bodies and dust grains to determine the resulting debris disk properties over a wide range of input parameters. We find that the relationship between planet mass and debris disk width is linear, with increasing planet mass producing broader debris rings. We apply our methods to five imaged debris rings to constrain the putative planet masses and orbits in each system. Observers can use our empirically derived equation as a guide for future direct imaging searches for planets in debris disk systems. In the fortuitous case of an imaged planet orbiting interior to an imaged disk, the planet's maximum mass can be estimated independent of atmospheric models.

The nature of the interaction between low-excitation gas filaments at ∼10⁴ K, seen in optical line emission, and diffuse X-ray emitting coronal gas at ∼10⁷ K in the centers of galaxy clusters remains a puzzle. The presence of a strong, empirical correlation between the two gas phases is indicative of a fundamental relationship between them, though as yet of undetermined cause. The cooler filaments, originally thought to have condensed from the hot gas, could also arise from a merger or the disturbance of cool circumnuclear gas by nuclear activity. Here, we have searched for intrinsic line emission polarization in cool core galaxy clusters as a diagnostic of fundamental transport processes. Drawing on developments in solar astrophysics, direct energetic particle impact induced polarization holds the promise to definitively determine the role of collisional processes such as thermal conduction in the ISM physics of galaxy clusters, while providing insight into other highly anisotropic excitation mechanisms such as shocks, intense radiation fields, and suprathermal particles. Under certain physical conditions, theoretical calculations predict of the order of 10% polarization. Our observations of the filaments in four nearby cool core clusters place stringent upper limits (≲ 0.1%) on the presence of emission line polarization, requiring that if thermal conduction is operative, the thermal gradients are not in the saturated regime. This limit is consistent with theoretical models of the thermal structure of filament interfaces.

We describe X-ray observations with Chandra and XMM-Newton of 18 M_group ∼ 1–6 × 10¹³ M_☉, z ∼ 0.05 galaxy groups from the Zurich ENvironmental Study. The X-ray data aim at establishing the frequency and properties, unaffected by host galaxy dilution and obscuration, of active galactic nuclei (AGNs) in central and satellite galaxies, also as a function of halo-centric distance. X-ray point-source detections are reported for 22 of the 177 galaxies, down to a sensitivity level of f_{0.5 − 8 keV} ∼ 5 × 10⁻¹⁵ erg cm⁻² s⁻¹, corresponding to a limiting luminosity of L_{0.5 − 8 keV} ∼ 3 × 10⁴⁰ erg s⁻¹. With the majority of the X-ray sources attributed to AGNs of low-to-moderate levels (L/L_Edd ≳ 10⁻⁴), we discuss the detection rate in the context of the occupation of AGNs to halos of this mass scale and redshift and compare the structural and morphological properties between AGN-active and non-active galaxies. At galaxy mass scales <10¹¹ M_☉, central galaxies appear to be a factor of ∼4 more likely to host AGNs than satellite galaxies of similar mass. This effect, coupled with the tendency for AGNs to be hosted by massive galaxies, explains the (weak) trend for AGNs to be preferentially found in the inner parts of group halos, with no detectable trend with halo-centric distance in the frequency of AGNs within the satellite population. Finally, our data indicate that the rate of decline with redshift of AGN activity in galaxy groups matches that of the global AGN population, indicating that either AGN activity occurs preferentially in group halos or that the evolution rate is independent of halo mass.

On the basis of the quantum electrodynamics, we present a generic formalism of the polarization for beamed monochromatic photons scattered by electrons in any spectral distribution. The formulae reduce to the components of the Fano matrix when electrons are at rest. We mainly investigate the polarization in three scenarios, i.e., electrons at rest, isotropic electrons with a power-law spectrum, and thermal electrons. If the incident beam is polarized, the polarization is reduced significantly by isotropic electrons at large viewing angles; the degree of polarization caused by thermal electrons is about half of that caused by power-law electrons. If the incident bean is unpolarized, soft γ-rays can lead to about 15% polarization at viewing angles around π/4. For isotropic electrons, one remarkable feature is that the polarization as a function of the incident photon energy always peaks roughly at 1 MeV; this is valid for both the thermal and power-law cases. This feature can be used to distinguish the model of the inverse Compton scattering from that of the synchrotron radiation.

In an effort to secure, refine, and supplement the relation between central supermassive black hole masses, M_•, and the bulge luminosities of their host galaxies, L_bul, we obtained deep, high spatial resolution K-band images of 35 nearby galaxies with securely measured M_•, using the wide-field WIRCam imager at the Canada–France–Hawaii–Telescope. A dedicated data reduction and sky subtraction strategy was adopted to estimate the brightness and structure of the sky, a critical step when tracing the light distribution of extended objects in the near-infrared. From the final image product, bulge and total magnitudes were extracted via two-dimensional profile fitting. As a first order approximation, all galaxies were modeled using a simple Sérsic-bulge+exponential-disk decomposition. However, we found that such models did not adequately describe the structure that we observed in a large fraction of our sample galaxies which often include cores, bars, nuclei, inner disks, spiral arms, rings, and envelopes. In such cases, we adopted profile modifications and/or more complex models with additional components. The derived bulge magnitudes are very sensitive to the details and number of components used in the models, although total magnitudes remain almost unaffected. Usually, but not always, the luminosities and sizes of the bulges are overestimated when a simple bulge+disk decomposition is adopted in lieu of a more complex model. Furthermore, we found that some spheroids are not well fit when the ellipticity of the Sérsic model is held fixed. This paper presents the details of the image processing and analysis, while we discuss how model-induced biases and systematics in bulge magnitudes impact the M_•–L_bul relation in a companion paper.

We present an investigation of the scaling relations between supermassive black hole (SMBH) masses, M_•, and their host galaxies' K-band bulge (L_bul) and total (L_tot) luminosities. The wide-field WIRCam imager at the Canada–France–Hawaii–Telescope was used to obtain the deepest and highest resolution near-infrared images available for a sample of 35 galaxies with securely measured M_•, selected irrespective of Hubble type. For each galaxy, we derive bulge and total magnitudes using a two-dimensional image decomposition code that allows us to account, if necessary, for large- and small-scale disks, cores, bars, nuclei, rings, envelopes, and spiral arms. We find that the present-day M_•–L_bul and M_•–L_tot relations have consistent intrinsic scatter, suggesting that M_• correlates equally well with bulge and total luminosity of the host. Our analysis provides only mild evidence of a decreased scatter if the fit is restricted to elliptical galaxies. The log-slopes of the M_•–L_bul and M_•–L_tot relations are 0.75 ± 0.10 and 0.92 ± 0.14, respectively. However, while the slope of the M_•–L_bul relation depends on the detail of the image decomposition, the characterization of M_•–L_tot does not. Given the difficulties and ambiguities of decomposing galaxy images into separate components, our results indicate that L_tot is more suitable as a tracer of SMBH mass than L_bul, and that the M_•–L_tot relation should be used when studying the co-evolution of SMBHs and galaxies.

The CH radical offers a sensitive way to test the hypothesis that fundamental constants measured on earth may differ from those observed in other parts of the universe. The starting point for such a comparison is to have accurate laboratory frequencies. Here, we measure the frequency of the lowest millimeter-wave transition of CH, near 535 GHz, with an accuracy of 0.6 kHz. This improves the uncertainty by roughly two orders of magnitude over previous determinations and opens the way for sensitive new tests of varying constants.

We have discovered two molecular features at radial velocities of −35 km s⁻¹ and 0 km s⁻¹ toward the infrared Double Helix Nebula (DHN) in the Galactic center with NANTEN2. The two features show good spatial correspondence with the DHN. We have also found two elongated molecular ridges at these two velocities distributed vertically to the Galactic plane over 08. The two ridges are linked by broad features in velocity and are likely connected physically with each other. The ratio between the ¹²CO J = 2–1 and J = 1–0 transitions is 0.8 in the ridges which is larger than the average value 0.5 in the foreground gas, suggesting the two ridges are in the Galactic center. An examination of the K band extinction reveals a good coincidence with the CO 0 km s⁻¹ ridge and is consistent with a distance of 8 ± 2 kpc. We discuss the possibility that the DHN was created by a magnetic phenomenon incorporating torsional Alfvén waves launched from the circum-nuclear disk and present a first estimate of the mass and energy involved in the DHN.

Fermi has provided the largest sample of γ-ray-selected blazars to date. In this work we use a uniformly selected set of 211 BL Lacertae (BL Lac) objects detected by Fermi during its first year of operation. We obtained redshift constraints for 206 out of the 211 BL Lac objects in our sample, making it the largest and most complete sample of BL Lac objects available in the literature. We use this sample to determine the luminosity function of BL Lac objects and its evolution with cosmic time. We find that for most BL Lac classes the evolution is positive, with a space density peaking at modest redshift (z ≈ 1.2). Low-luminosity, high-synchrotron–peaked (HSP) BL Lac objects are an exception, showing strong negative evolution, with number density increasing for z ≲ 0.5. Since this rise corresponds to a drop-off in the density of flat-spectrum radio quasars (FSRQs), a possible interpretation is that these HSPs represent an accretion-starved end state of an earlier merger-driven gas-rich phase. We additionally find that the known BL Lac correlation between luminosity and photon spectral index persists after correction for the substantial observational selection effects with implications for the so-called "blazar sequence." Finally, by estimating the beaming corrections to the luminosity function, we find that BL Lac objects have an average Lorentz factor of $\gamma =6.1^{+1.1}_{-0.8}$, and that most are seen within 10° of the jet axis.

Cosmological hydrodynamic simulations predict the physical state of baryons in the circumgalactic medium (CGM), which can be directly tested via quasar absorption line observations. We use high-resolution "zoom-in" simulations of 21 galaxies to characterize the distribution of neutral hydrogen around halos in the mass range M_vir ∼ 2 × 10¹¹ to 4 × 10¹² M_☉ at z ∼ 2. We find that both the mass fraction of cool (T ⩽ 3 × 10⁴ K) gas and the covering fraction of optically thick Lyman limit systems (LLSs) depend only weakly on halo mass, even around the critical value for the formation of stable virial shocks. The covering fraction of LLSs interior to the virial radius varies between f_c ∼ 0.05–0.2, with significant scatter among halos. Our simulations of massive halos (M_vir ⩾ 10¹² M_☉) underpredict the covering fraction of optically thick gas observed in the quasar CGM by a large factor. The reason for this discrepancy is unclear, but several possibilities are discussed. In the lower mass halos (M_vir ⩾ 5 × 10¹¹ M_☉) hosting star-forming galaxies, the predicted covering factor agrees with observations; however, current samples of quasar–galaxy pairs are too small for a conclusive comparison. To overcome this limitation, we propose a new observable: the small-scale autocorrelation function of optically thick absorbers detected in the foreground of close quasar pairs. We show that this new observable can constrain the underlying dark halos hosting LLSs at z ∼ 2–3, as well as the characteristic size and covering factor of the CGM.

We present a method for selecting z > 4 dusty, star-forming galaxies (DSFGs) using Herschel/Spectral and Photometric Imaging Receiver 250/350/500 μm flux densities to search for red sources. We apply this method to 21 deg² of data from the HerMES survey to produce a catalog of 38 high-z candidates. Follow-up of the first five of these sources confirms that this method is efficient at selecting high-z DSFGs, with 4/5 at z = 4.3–6.3 (and the remaining source at z = 3.4), and that they are some of the most luminous dusty sources known. Comparison with previous DSFG samples, mostly selected at longer wavelengths (e.g., 850 μm) and in single-band surveys, shows that our method is much more efficient at selecting high-z DSFGs, in the sense that a much larger fraction are at z > 3. Correcting for the selection completeness and purity, we find that the number of bright (S_500 μm ⩾ 30 mJy), red Herschel sources is 3.3 ± 0.8 deg⁻². This is much higher than the number predicted by current models, suggesting that the DSFG population extends to higher redshifts than previously believed. If the shape of the luminosity function for high-z DSFGs is similar to that at z ∼ 2, rest-frame UV based studies may be missing a significant component of the star formation density at z = 4–6, even after correction for extinction.

Absorption-line spectroscopy is a powerful tool used to estimate element abundances in both the nearby and distant universe. The accuracy of the abundances thus derived is naturally limited by the accuracy of the atomic data assumed for the spectral lines. We have recently started a project to perform new extensive atomic data calculations used for optical/UV spectral lines in the plasma modeling code Cloudy using state of the art quantal calculations. Here, we demonstrate our approach by focussing on S ii, an ion used to estimate metallicities for Milky Way interstellar clouds as well as distant damped Lyman-alpha (DLA) and sub-DLA absorber galaxies detected in the spectra of quasars and gamma-ray bursts. We report new extensive calculations of a large number of energy levels of S ii, and the line strengths of the resulting radiative transitions. Our calculations are based on the configuration interaction approach within a numerical Hartree–Fock framework, and utilize both non-relativistic and quasirelativistic one-electron radial orbitals. The results of these new atomic calculations are then incorporated into Cloudy and applied to a lab plasma, and a typical DLA, for illustrative purposes. The new results imply relatively modest changes (≈0.04 dex) to the metallicities estimated from S ii in past studies. These results will be readily applicable to other studies of S ii in the Milky Way and other galaxies.

We present the morphological properties of Hα-selected galaxies at z > 2 in SXDF-UDS-CANDELS field. With high-resolution optical/near-infrared images obtained by the Hubble Space Telescope, we identify giant clumps within the Hα emitters (HAEs). We find that at least 41% of our sample shows clumpy structures in the underlying disks. The color gradient of clumps is commonly seen in the sense that the clumps near the galactic center tend to be redder than those in the outer regions. The mid-infrared detection in galaxies with red clumps and the spatial distribution of Hα emission suggest that dusty star-formation activity is probably occurring in the nuclear red clumps. A gas supply to a bulge component through clump migration is one of the most potent physical processes for producing such dusty star-forming clumps and forming massive bulges in local early-type galaxies. They would become large quiescent galaxies at later times just by consumption or blowout of remaining gas. Also, while most of the HAEs have extended disks, we observe two massive, compact HAEs whose stellar surface densities are significantly higher. They are likely to be the direct progenitors of massive, compact quiescent galaxies at z = 1.5–2.0. Two evolutionary paths to massive quiescent galaxies are devised to account for both the size growth of quiescent galaxies and their increased number density from z ∼ 2 to z = 0.

The black hole binary Cygnus X-1 was observed in late 2012 with the Nuclear Spectroscopic Telescope Array (NuSTAR) and Suzaku, providing spectral coverage over the ∼1–300 keV range. The source was in the soft state with a multi-temperature blackbody, power law, and reflection components along with absorption from highly ionized material in the system. The high throughput of NuSTAR allows for a very high quality measurement of the complex iron line region as well as the rest of the reflection component. The iron line is clearly broadened and is well described by a relativistic blurring model, providing an opportunity to constrain the black hole spin. Although the spin constraint depends somewhat on which continuum model is used, we obtain a_* > 0.83 for all models that provide a good description of the spectrum. However, none of our spectral fits give a disk inclination that is consistent with the most recently reported binary values for Cyg X-1. This may indicate that there is a >13° misalignment between the orbital plane and the inner accretion disk (i.e., a warped accretion disk) or that there is missing physics in the spectral models.

We study the dynamics of super-Eddington accretion flows by performing two-dimensional radiation-hydrodynamic simulations. Compared with previous works, in this paper we include the T_θϕ component of the viscous stress and consider various values of the viscous parameter α. We find that when T_θϕ is included, the rotational speed of the high-latitude flow decreases, while the density increases and decreases at the high and low latitudes, respectively. We calculate the radial profiles of inflow and outflow rates. We find that the inflow rate decreases inward, following a power law form of $\dot{M}_{\rm in}\propto r^s$. The value of s depends on the magnitude of α and is within the range of ∼0.4–1.0. Correspondingly, the radial profile of density becomes flatter compared with the case of a constant $\dot{M}(r)$. We find that the density profile can be described by ρ(r)∝r^−p and the value of p is almost same for a wide range of α ranging from α = 0.1 to 0.005. The inward decrease of inflow accretion rate is very similar to hot accretion flows, which is attributed to the mass loss in outflows. To study the origin of outflow, we analyze the convective stability of the slim disk. We find that depending on the value of α, the flow is marginally stable (when α is small) or unstable (when α is large). This is different from the case of hydrodynamical hot accretion flow, where radiation is dynamically unimportant and the flow is always convectively unstable. We speculate that the reason for the difference is because radiation can stabilize convection. The origin of outflow is thus likely because of the joint function of convection and radiation, but further investigation is required.

In the single-degenerate scenario for the progenitors of Type Ia supernovae (SNe Ia), a white dwarf rapidly accretes hydrogen- or helium-rich material from its companion star and appears as a supersoft X-ray source. This picture has been challenged by the properties of the supersoft X-ray sources with very low mass companions and the observations of several nearby SNe Ia. It has been pointed out that the X-ray radiation or the wind from the accreting white dwarf can excite winds or strip mass from the companion star, thus significantly influencing the mass transfer processes. In this paper, we perform detailed calculations of the wind-driven evolution of white dwarf binaries. We present the parameter space for the possible SN Ia progenitors and for the surviving companions after the SNe. The results show that the ex-companion stars of SNe Ia have characteristics more compatible with the observations, compared with those in the traditional single-degenerate scenario.

Simulations of hot, pressure-supported, tilted black hole accretion flows, in which the angular momentum of the flow is misaligned with the black hole spin axis, can exhibit two nonaxisymmetric shock structures in the inner regions of the flow. We analyze the strength and significance of these shock structures in simulations with tilt angles of 10° and 15°. By integrating fluid trajectories in the simulations through the shocks and tracking the variations of fluid quantities along these trajectories, we show that these shocks are strong, with substantial compression ratios, in contrast to earlier claims. However, they are only moderately relativistic. We also show that the two density enhancements resembling flow streams in their shape are in fact merely post-shock compressions, as fluid trajectories cut across, rather than flow along, them. The dissipation associated with the shocks is a substantial fraction (≃ 3%–12%) of the rest mass energy advected into the hole, and therefore comparable to the dissipation expected from turbulence. The shocks should therefore make order unity changes in the observed properties of black hole accretion flows that are tilted.

Although the widely used analytical afterglow model of gamma-ray bursts (GRBs) predicts a sharp cooling break ν_c in its afterglow spectrum, the GRB observations so far rarely show clear evidence for a cooling break in their spectra or a corresponding temporal break in their light curves. Employing a Lagrangian description of the blast wave, we conduct a sophisticated calculation of the afterglow emission. We precisely follow the cooling history of non-thermal electrons accelerated into each Lagrangian shell. We show that a detailed calculation of afterglow spectra does not in fact give rise to a sharp cooling break at ν_c. Instead, it displays a very mild and smooth transition, which occurs gradually over a few orders of magnitude in energy or frequency. The main source of this slow transition is that different mini shells have different evolutionary histories of the comoving magnetic field strength B, so that deriving the current value of ν_c of each mini shell requires an integration of its cooling rate over the time elapsed since its creation. We present the time evolution of optical and X-ray spectral indices to demonstrate the slow transition of spectral regimes and discuss the implications of our result in interpreting GRB afterglow data.

We have created 0.3–10 keV, 13 yr, unabsorbed luminosity lightcurves for 528 X-ray sources in the central 20' of M31. We have 174 Chandra observations spaced at ∼1 month intervals due to our transient monitoring program, deeper observations of the M31 nucleus, and some public data from other surveys. We created 0.5–4.5 keV structure functions (SFs) for each source for comparison with the ensemble SF of active galactic nuclei (AGN). We find 220 X-ray sources with luminosities ≳10³⁵ erg s⁻¹ that have SFs with significantly more variability than the ensemble AGN SF, and which are likely X-ray binaries (XBs). A further 30 X-ray sources were identified as XBs using other methods. We therefore have 250 probable XBs in total, including ∼200 new identifications. This result represents great progress over the ∼50 XBs and ∼40 XB candidates previously identified out of the ∼2000 X-ray sources within the D₂₅ region of M31; it also demonstrates the power of SF analysis for identifying XBs in external galaxies. We also identify a new transient black hole candidate, associated with the M31 globular cluster B128.

We study the interaction of an unequal-mass binary with an isothermal circumbinary disk, motivated by the theoretical and observational evidence that after a major merger of gas-rich galaxies, a massive gaseous disk with a supermassive black hole binary will be formed in the nuclear region. We focus on the gravitational torques that the binary exerts on the disk and how these torques can drive the formation of a gap in the disk. This exchange of angular momentum between the binary and the disk is mainly driven by the gravitational interaction between the binary and a strong nonaxisymmetric density perturbation that is produced in the disk, in response to the presence of the binary. Using smoothed particle hydrodynamics numerical simulations, we test two gap-opening criteria, one that assumes the geometry of the density perturbation is an ellipsoid/thick spiral and another that assumes a flat spiral geometry for the density perturbation. We find that the flat spiral gap-opening criterion successfully predicts which simulations will have a gap in the disk and which will not. We also study the limiting cases predicted by the gap-opening criteria. Since the viscosity in our simulations is considerably smaller than the expected value in the nuclear regions of gas-rich merging galaxies, we conclude that in such environments the formation of a circumbinary gap is unlikely.

It is currently assumed that infrared dark clouds (IRDCs) represent the earliest evolutionary stages of high-mass stars (>8 M_☉). Submillimeter and millimeter-wave studies performed over the past 15 yr show that IRDCs possess a broad variety of properties, and hence a wide range of problems and questions that can be tackled. In this paper, we report an investigation of the molecular composition and chemical processes in two groups of IRDCs. Using the Mopra, APEX, and IRAM radio telescopes over the last four years, we have collected molecular line data for CO, H₂CO, HNCO, CH₃CCH, CH₃OH, CH₃CHO, CH₃OCHO, and CH₃OCH₃. For all of these species we estimated molecular abundances. We then undertook chemical modeling studies, concentrating on the source IRDC028.34+0.06, and compared observed and modeled abundances. This comparison showed that to reproduce observed abundances of complex organic molecules, a zero-dimensional gas-grain model with constant physical conditions is not sufficient. We achieved greater success with the use of a warm-up model, in which warm-up from 10 K to 30 K occurs following a cold phase.

Recent theoretical and observational works indicate the presence of a correlation between the star-formation rate (SFR) and active galactic nucleus (AGN) luminosity (and, therefore, the black hole accretion rate, $\dot{M}_{\rm BH}$) of Seyfert galaxies. This suggests a physical connection between the gas-forming stars on kpc scales and the gas on sub-pc scales that is feeding the black hole. We compiled the largest sample of Seyfert galaxies to date with high angular resolution (∼04–08) mid-infrared (8–13 μm) spectroscopy. The sample includes 29 Seyfert galaxies drawn from the AGN Revised Shapley–Ames catalog. At a median distance of 33 Mpc, our data allow us to probe nuclear regions on scales of ∼65 pc (median value). We found no general evidence of suppression of the 11.3 μm polycyclic aromatic hydrocarbon (PAH) emission in the vicinity of these AGN, and we used this feature as a proxy for the SFR. We detected the 11.3 μm PAH feature in the nuclear spectra of 45% of our sample. The derived nuclear SFRs are, on average, five times lower than those measured in circumnuclear regions of 600 pc in size (median value). However, the projected nuclear SFR densities (median value of 22 M_☉ yr⁻¹ kpc⁻²) are a factor of 20 higher than those measured on circumnuclear scales. This indicates that the SF activity per unit area in the central ∼65 pc region of Seyfert galaxies is much higher than at larger distances from their nuclei. We studied the connection between the nuclear SFR and $\dot{M}_{\rm BH}$ and showed that numerical simulations reproduce our observed relation fairly well.

The author presents a model for variability of the flux and polarization of blazars in which turbulent plasma flowing at a relativistic speed down a jet crosses a standing conical shock. The shock compresses the plasma and accelerates electrons to energies up to γ_max ≳ 10⁴ times their rest-mass energy, with the value of γ_max determined by the direction of the magnetic field relative to the shock front. The turbulence is approximated in a computer code as many cells, each with a uniform magnetic field whose direction is selected randomly. The density of high-energy electrons in the plasma changes randomly with time in a manner consistent with the power spectral density of flux variations derived from observations of blazars. The variations in flux and polarization are therefore caused by continuous noise processes rather than by singular events such as explosive injection of energy at the base of the jet. Sample simulations illustrate the behavior of flux and linear polarization versus time that such a model produces. The variations in γ-ray flux generated by the code are often, but not always, correlated with those at lower frequencies, and many of the flares are sharply peaked. The mean degree of polarization of synchrotron radiation is higher and its timescale of variability shorter toward higher frequencies, while the polarization electric vector sometimes randomly executes apparent rotations. The slope of the spectral energy distribution exhibits sharper breaks than can arise solely from energy losses. All of these results correspond to properties observed in blazars.

Isolated dwarf galaxies, especially those situated in voids, may provide insight into primordial conditions in the universe and the physical processes that govern star formation in undisturbed stellar systems. The metallicity of H ii regions in such galaxies is key to investigating this possibility. From the SIGRID sample of isolated dwarf galaxies, we have identified two exceptionally isolated objects, the Local Void galaxy [KK98]246 (ESO 461-G036) and another somewhat larger dwarf irregular on the edge of the Local Void, MCG-01-41-006 (HIPASS J1609-04). We report our measurements of the nebular metallicities in these objects. The first object has a single low luminosity H ii region, while the second is in a more vigorous star forming phase with several bright H ii regions. We find that the metallicities in both galaxies are typical for galaxies of this size, and do not indicate the presence of any primordial gas, despite (for [KK98]246) the known surrounding large reservoir of neutral hydrogen.

The Cerenkov line-like radiation in a dense gas (N_H > 10¹³ cm⁻³) is potentially important in the exploration of the optical broad emission lines of quasars and Seyfert 1 galaxies. With this quasi-line emission mechanism, some long standing puzzles in the study of quasars could be resolved. In this paper, we calculate the power of the Cerenkov line-like radiation in dense gas and compare with the powers of other radiation mechanisms by a fast electron to confirm its importance. From the observed gamma-ray luminosity of 3C 279, we show that the total number of fast electrons is sufficiently high to allow effective operation of the quasi-line emission. We present a model calculation for the luminosity of the Cerenkov Lyα line of 3C 279, which is high enough to compare with observations. We therefore conclude that the broad line of quasars may be a blend of the Cerenkov emission line with the real line produced by the bound-bound transition. A new approach to the absorption of the Cerenkov line is presented with the method of escape probability, which markedly simplifies the computation in the optically thick case. The revised set of formulae for the Cerenkov line-like radiation is more convenient in applications.

We have used a combination of high-resolution Hubble Space Telescope Wide Field Planetary Camera 2 and wide-field ground-based observations, in ultraviolet and optical bands, to study the blue straggler star population of the massive outer halo globular cluster NGC 5824 over its entire radial extent. We have computed the center of the cluster and constructed the radial density profile from detailed star counts. The profile is well reproduced by a Wilson model with a small core (r_c ≃ 44) and a concentration parameter c ≃ 2.74. We also present the first age determination for this cluster. From a comparison with isochrones, we find t = 13 ± 0.5 Gyr. We discuss this result in the context of the observed age–metallicity relation of Galactic globular clusters. A total of 60 bright blue stragglers has been identified. Their radial distribution is found to be bimodal, with a central peak, a well-defined minimum at r ∼ 20'', and an upturn at large radii. In the framework of the dynamical clock recently defined by Ferraro et al., this feature suggests that NGC 5824 is a cluster of intermediate dynamical age.

We present the radial velocity curve of a single-lined spectroscopic binary in the faint Hercules dwarf spheroidal (dSph) galaxy, based on 34 individual spectra covering more than 2 yr of observations. This is the first time that orbital elements could be derived for a binary in a dSph. The system consists of a metal-poor red giant and a low-mass companion, possibly a white dwarf, with a 135 day period in a moderately eccentric (e = 0.18) orbit. Its period and eccentricity are fully consistent with metal-poor binaries in the Galactic halo, while the projected semimajor axis is small, at a_p sin  i = 38 R_☉. In fact, a very close orbit could inhibit the production of heavier elements through s-process nucleosynthesis, leading to the very low abundances of neutron-capture elements that are found in this star. We discuss the further implications for the chemical enrichment history of the Hercules dSph, but find no compelling binary scenario that could reasonably explain the full, peculiar abundance pattern of the Hercules dSph galaxy.

We present and discuss an extensive data set for the non-Blazhko ab-type RR Lyrae star SDSS J015450+001501, including optical Sloan Digital Sky Survey ugriz light curves and spectroscopic data, LINEAR and Catalina Sky Survey unfiltered optical light curves, and infrared Two Micron All Sky Survey (2MASS) JHK_s and Wide-field Infrared Survey ExplorerW1 and W2 light curves. Most notable is that light curves obtained by 2MASS include close to 9000 photometric measures collected over 3.3 yr and provide an exceedingly precise view of near-infrared variability. These data demonstrate that static atmosphere models are insufficient to explain multiband photometric light-curve behavior and present strong constraints for nonlinear pulsation models for RR Lyrae stars. It is a challenge to modelers to produce theoretical light curves that can explain data presented here, which we make publicly available.

The "abundance discrepancy" problem in the study of planetary nebulae (PNe), viz., the problem concerning systematically higher heavy-element abundances derived from optical recombination lines relative to those from collisionally excited lines, has been under discussion for decades, but no consensus on its solution has yet been reached. In this paper, we investigate the hydrogen free–bound emission near the Balmer jump region of four PNe that are among those with the largest abundance discrepancies, aiming to examine two recently proposed solutions to this problem: two-component models and κ electron energy distributions. We find that the Balmer jump intensities and the spectrum slopes cannot be simultaneously matched by the theoretical calculations based upon single Maxwell–Boltzmann electron-energy distributions, whereas the fitting can be equally improved by introducing κ electron energy distributions or an additional Maxwell–Boltzmann component. We show that although H i free–bound emission alone cannot distinguish between the two scenarios, it can provide important constraints on the electron energy distributions, especially for cold and low-κ plasmas.

47 Tuc is an ideal target to study chemical evolution and globular cluster (GC) formation in massive more metal-rich GCs, as it is the closest massive GC. We present chemical abundances for O, Na, Al, Si, Ca, Ti, Fe, Ni, La, and Eu in 164 red giant branch stars in the massive GC 47 Tuc using spectra obtained with both the Hydra multifiber spectrograph at the Blanco 4 m telescope and the FLAMES multiobject spectrograph at the Very Large Telescope. We find an average [Fe/H] = −0.79 ± 0.09 dex, consistent with literature values, as well as overabundances of alpha-elements ([α/Fe] ∼ 0.3 dex). The n-capture process elements indicate that 47 Tuc is r process-dominated ([Eu/La] = +0.24), and the light elements O, Na, and Al exhibit star-to-star variations. The Na-O anticorrelation, a signature typically seen in Galactic GCs, is present in 47 Tuc, and extends to include a small number of stars with [O/Fe] ∼ −0.5. Additionally, the [O/Na] ratios of our sample reveal that the cluster stars can be separated into three distinct populations. A Kolmogorov–Smirnov test demonstrates that the O-poor/Na-rich stars are more centrally concentrated than the O-rich/Na-poor stars. The observed number and radial distribution of 47 Tuc's stellar populations, as distinguished by their light element composition, agrees closely with the results obtained from photometric data. We do not find evidence supporting a strong Na–Al correlation in 47 Tuc, which is consistent with current models of asymptotic giant branch nucleosynthesis yields.

We present model predictions for the Zr isotopic ratios produced by slow neutron captures in C-rich asymptotic giant branch (AGB) stars of masses 1.25–4 M_☉ and metallicities Z = 0.01–0.03, and compare them to data from single meteoritic stardust silicon carbide (SiC) and high-density graphite grains that condensed in the outflows of these stars. We compare predictions produced using the Zr neutron-capture cross sections from Bao et al. and from n_TOF experiments at CERN, and present a new evaluation for the neutron-capture cross section of the unstable isotope ⁹⁵Zr, the branching point leading to the production of ⁹⁶Zr. The new cross sections generally present an improved match with the observational data, except for the ⁹²Zr/⁹⁴Zr ratios, which are on average still substantially higher than predicted. The ⁹⁶Zr/⁹⁴Zr ratios can be explained using our range of initial stellar masses, with the most ⁹⁶Zr-depleted grains originating from AGB stars of masses 1.8–3 M_☉ and the others from either lower or higher masses. The ^{90, 91}Zr/⁹⁴Zr variations measured in the grains are well reproduced by the range of stellar metallicities considered here, which is the same needed to cover the Si composition of the grains produced by the chemical evolution of the Galaxy. The ⁹²Zr/⁹⁴Zr versus ²⁹Si/²⁸Si positive correlation observed in the available data suggests that stellar metallicity rather than rotation plays the major role in covering the ^{90, 91, 92}Zr/⁹⁴Zr spread.

Supernovae (SNe) powered by interaction with circumstellar material provide evidence for intense stellar mass loss during the final years before core collapse. We have argued that during and after core neon burning, internal gravity waves excited by core convection can tap into the core fusion power and transport a super-Eddington energy flux out to the stellar envelope, potentially unbinding ∼1 solar mass of material. In this work, we explore the internal conditions of SN progenitors using the MESA one-dimensional stellar evolution code in search of those most susceptible to wave-driven mass loss. We focus on simple, order of magnitude considerations applicable to a wide range of progenitors. Wave-driven mass loss during core neon and oxygen fusion happens preferentially in either lower mass (∼20 solar mass zero-age main sequence) stars or massive, sub-solar metallicity stars. Roughly 20% of the SN progenitors we survey can excite 10^46–48 erg of energy in waves that can potentially drive mass loss within a few months to a decade of core collapse. This energy can generate circumstellar environments with 10⁻³–1 solar masses reaching 100 AU before explosion. We predict a correlation between the energy associated with pre-SN mass ejection and the time to core collapse, with the most intense mass loss preferentially occurring closer to core collapse. During silicon burning, wave energy may inflate 10⁻³–1 solar masses of the envelope to 10–100 s of solar radii. This suggests that some nominally compact SN progenitors (Type Ibc progenitors) will have a significantly different SN shock breakout signature than traditionally assumed.

We present Herschel far-infrared and submillimeter maps of the debris disk associated with the HR 8799 planetary system. We resolve the outer disk emission at 70, 100, 160, and 250 μm and detect the disk at 350 and 500 μm. A smooth model explains the observed disk emission well. We observe no obvious clumps or asymmetries associated with the trapping of planetesimals that is a potential consequence of planetary migration in the system. We estimate that the disk eccentricity must be <0.1. As in previous work by Su et al., we find a disk with three components: a warm inner component and two outer components, a planetesimal belt extending from 100 to 310 AU, with some flexibility (±10 AU) on the inner edge, and the external halo that extends to ∼2000 AU. We measure the disk inclination to be 26°  ±  3° from face-on at a position angle of 64° E of N, establishing that the disk is coplanar with the star and planets. The spectral energy distribution of the disk is well fit by blackbody grains whose semi-major axes lie within the planetesimal belt, suggesting an absence of small grains. The wavelength at which the spectrum steepens from blackbody, 47 ± 30 μm, however, is short compared with other A star debris disks, suggesting that there are atypically small grains likely populating the halo. The PACS longer wavelength data yield a lower disk color temperature than do MIPS data (24 and 70 μm), implying two distinct halo dust-grain populations.

Energetic neutral atoms (ENAs) observed by the Interstellar Boundary Explorer (IBEX) provide powerful diagnostics about the origin of the progenitor ion populations and the physical mechanisms responsible for their production. In this paper, we extend the work of Desai et al. and Fuselier et al. and combine and compare ENA spectra from the first 3 yr of observations by the IBEX-Hi and -Lo ENA imagers along the lines-of-sight (LOSs) from the inner heliosphere through to the locations of Voyager 1 and 2 with results from an updated physics-based model of the three-dimensional heliosphere and its constituent ion populations. Our results show that (1) IBEX ENA fluxes and spectra above ∼0.7 keV measured along the LOSs of the Voyagers are consistent with several models in which the parent pickup ion (PUI) populations originate in the inner heliosheath, and (2) a significant fraction of lower energy ENAs between ∼0.1–0.5 keV may originate from interstellar neutral gas charge-exchanging with a non-thermalized (hot) population of PUIs in the outer heliosheath beyond the heliopause. We discuss the implications of ENAs observed by IBEX originating from distinct parent populations as well as from two distinct locations in the heliospheric interface. These results indicate that ENA spectral measurements at various energies can be used to remotely probe distinct physical processes operating in vastly different regions of the distant heliosphere.

Turbulence is ubiquitous in astrophysical fluids such as the interstellar medium and the intracluster medium. In turbulence studies, it is customary to assume that fluid is driven on a single scale. However, in astrophysical fluids, there can be many different driving mechanisms that act on different scales. If there are multiple energy-injection scales, the process of energy cascade and turbulence dynamo will be different compared with the case of the single energy-injection scale. In this work, we perform three-dimensional incompressible/compressible magnetohydrodynamic turbulence simulations. We drive turbulence in Fourier space in two wavenumber ranges, $2 \le k \le \sqrt{1}2$ (large scale) and 15 ≲ k ≲ 26 (small scale). We inject different amount of energy in each range by changing the amplitude of forcing in the range. We present the time evolution of the kinetic and magnetic energy densities and discuss the turbulence dynamo in the presence of energy injections at two scales. We show how kinetic, magnetic, and density spectra are affected by the two-scale energy injections and we discuss the observational implications. In the case _L < _S, where _L and _S are energy-injection rates at the large and small scales, respectively, our results show that even a tiny amount of large-scale energy injection can significantly change the properties of turbulence. On the other hand, when _L ≳ _S, the small-scale driving does not influence the turbulence statistics much unless _L ∼ _S.

We present our parameterizations of the log([Ne iii]λ3869/[O ii]λ3727) (Ne3O2) and log([O iii]λ5007/[O ii]λ3727) (O3O2) ratios as diagnostics of ionization parameter in star-forming galaxies. Our calibrations are based on the Starburst99/Mappings III photoionization models, which extend up to the extremely high values of ionization parameter found in high-redshift galaxies. While similar calibrations have been presented previously for O3O2, this is the first such calibration of Ne3O2. We illustrate the tight correlation between these two ratios for star-forming galaxies and discuss the underlying physics that dictates their very similar evolution. Based on this work, we propose the Ne3O2 ratio as a new and useful diagnostic of ionization parameter for star-forming galaxies. Given the Ne3O2 ratio's relative insensitivity to reddening, this ratio is particularly valuable for use with galaxies that have uncertain amounts of extinction. The short wavelengths of the Ne3O2 ratio can also be applied out to very high redshifts, extending studies of galaxies' ionization parameters out to z ∼ 1.6 with optical spectroscopy and z ∼ 5.2 with ground-based near-infrared spectra.

We develop a nonlinear force-free field (NLFFF) extrapolation code based on the magnetohydrodynamic (MHD) relaxation method. We extend the classical MHD relaxation method in two important ways. First, we introduce an algorithm initially proposed by Dedner et al. to effectively clean the numerical errors associated with ∇ · B. Second, the multigrid type method is implemented in our NLFFF to perform direct analysis of the high-resolution magnetogram data. As a result of these two implementations, we successfully extrapolated the high resolution force-free field introduced by Low & Lou with better accuracy in a drastically shorter time. We also applied our extrapolation method to the MHD solution obtained from the flux-emergence simulation by Magara. We found that NLFFF extrapolation may be less effective for reproducing areas higher than a half-domain, where some magnetic loops are found in a state of continuous upward expansion. However, an inverse S-shaped structure consisting of the sheared and twisted loops formed in the lower region can be captured well through our NLFFF extrapolation method. We further discuss how well these sheared and twisted fields are reconstructed by estimating the magnetic topology and twist quantitatively.

The theoretical concept that braided magnetic field lines in the solar corona may dissipate a sufficient amount of energy to account for the brightening observed in the active-region (AR) corona has only recently been substantiated by high-resolution observations. From the analysis of coronal images obtained with the High Resolution Coronal Imager, first observational evidence of the braiding of magnetic field lines was reported by Cirtain et al. (hereafter CG13). We present nonlinear force-free reconstructions of the associated coronal magnetic field based on Solar Dynamics Observatory/Helioseismic and Magnetic Imager vector magnetograms. We deliver estimates of the free magnetic energy associated with a braided coronal structure. Our model results suggest (∼100 times) more free energy at the braiding site than analytically estimated by CG13, strengthening the possibility of the AR corona being heated by field line braiding. We were able to appropriately assess the coronal free energy by using vector field measurements and we attribute the lower energy estimate of CG13 to the underestimated (by a factor of 10) azimuthal field strength. We also quantify the increase in the overall twist of a flare-related flux rope that was noted by CG13. From our models we find that the overall twist of the flux rope increased by about half a turn within 12 minutes. Unlike another method to which we compare our results, we evaluate the winding of the flux rope's constituent field lines around each other purely based on their modeled coronal three-dimensional field line geometry. To our knowledge, this is done for the first time here.

During the reversal of the Sun's polar fields at sunspot maximum, outward extrapolations of magnetograph measurements often predict the presence of two or more current sheets extending into the interplanetary medium, instead of the single heliospheric current sheet (HCS) that forms the basis of the standard "ballerina skirt" picture. By comparing potential-field source-surface models of the coronal streamer belt with white-light coronagraph observations, we deduce that the HCS was split into two distinct structures with circular cross sections during mid-2012. These cylindrical current sheets were centered near the heliographic equator and separated in longitude by roughly 180°; a corresponding four-sector polarity pattern was observed at Earth. Each cylinder enclosed a negative-polarity coronal hole that was identifiable in extreme ultraviolet images and gave rise to a high-speed stream. The two current sheet systems are shown to be a result of the dominance of the Sun's nonaxisymmetric quadrupole component, as the axial dipole field was undergoing its reversal during solar cycle 24.

We cross match the GALEX and Kepler surveys to create a unique dataset with both ultraviolet (UV) measurements and highly precise photometric variability measurements in the visible light spectrum. As stellar activity is driven by magnetic field modulations, we have used UV emission from the magnetically heated gas in the stellar atmosphere to serve as our proxy for the more well-known stellar activity indicator, R'_HK. The R'_HK approximations were in turn used to estimate the level of astrophysical noise expected in radial velocity (RV) measurements and these were then searched for correlations with photometric variability. We find significant scatter in our attempts to estimate RV noise for magnetically active stars, which we attribute to variations in the phase and strength of the stellar magnetic cycle that drives the activity of these targets. However, for stars we deem to be magnetically quiet, we do find a clear correlation between photometric variability and estimated levels of RV noise (with variability up to ∼10 m s⁻¹). We conclude that for these quiet stars, we can use photometric measurements as a proxy to estimate the RV noise expected. As a result, the procedure outlined in this paper may help select targets best-suited for RV follow-up necessary for planet confirmation.

We have mapped the distribution of young and old stars in the gaseous H i warp of NGC 4565. We find a clear correlation of young stars (<600 Myr) with the warp but no coincident old stars (>1 Gyr), which places an upper limit on the age of the structure. The formation rate of the young stars, which increased ∼300 Myr ago relative to the surrounding regions, is $(6.3^{+2.5}_{-1.5})\times 10^{-5}$ M_☉ yr⁻¹ kpc⁻². This implies a ∼60 ± 20 Gyr depletion time of the H i warp, similar to the timescales calculated for the outer H i disks of nearby spiral galaxies. While some stars associated with the warp fall into the asymptotic giant branch (AGB) region of the color–magnitude diagram, where stars could be as old as 1 Gyr, further investigation suggests that they may be interlopers rather than real AGB stars. We discuss the implications of these age constraints for the formation of H i warps and the gas fueling of disk galaxies.

We present the results of infrared K- (2.2 μm) and L'-band (3.8 μm) high-spatial-resolution (<02) imaging observations of nearby gas- and dust-rich infrared luminous merging galaxies, assisted by the adaptive optics system on the Subaru 8.2 m telescope. We investigate the presence and frequency of red K − L' compact sources, which are sensitive indicators of active galactic nuclei (AGNs), including AGNs that are deeply buried in gas and dust. We observed 29 merging systems and confirmed at least one AGN in all but one system. However, luminous dual AGNs were detected in only four of the 29 systems (∼14%), despite our method's being sensitive to buried AGNs. For multiple nuclei sources, we compared the estimated AGN luminosities with supermassive black hole (SMBH) masses inferred from large-aperture K-band stellar emission photometry in individual nuclei. We found that mass accretion rates onto SMBHs are significantly different among multiple SMBHs, such that larger-mass SMBHs generally show higher mass accretion rates when normalized to SMBH mass. Our results suggest that non-synchronous mass accretion onto SMBHs in gas- and dust-rich infrared luminous merging galaxies hampers the observational detection of kiloparsec-scale multiple active SMBHs. This could explain the significantly smaller detection fraction of kiloparsec-scale dual AGNs when compared with the number expected from simple theoretical predictions. Our results also indicate that mass accretion onto SMBHs is dominated by local conditions, rather than by global galaxy properties, reinforcing the importance of observations to our understanding of how multiple SMBHs are activated and acquire mass in gas- and dust-rich merging galaxies.

The limb flare SOL2012-07-19T05:58 (M7.7) provides the best example of a non-thermal above-the-loop-top hard X-ray source with simultaneous observations by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory. By combining the two sets of observations, we present the first direct measurement of the thermal proton density and non-thermal electron density within the above-the-loop-top source where particle acceleration occurs. We find that both densities are of the same order of magnitude of a few times 10⁹ cm⁻³, about 30 times lower than the density in the underlying thermal flare loops. The equal densities indicate that the entire electron population within the above-the-loop-top source is energized. While the derived densities depend on the unknown source depth and filling factor, the ratio of these two densities does not. Within the uncertainties, the ratio is one for a low energy cutoff of the non-thermal electron spectrum between 10 and 15 keV. RHESSI observations only constrain the cutoff energy to below ∼15 keV, leaving the spectral shape of the electrons within the above-the-loop-top source at lower energies unknown. Nevertheless, these robust results strongly corroborate earlier findings that the above-the-loop-top source is the acceleration region where a bulk energization process acts on all electrons.

We present new Hubble Space Telescope observations of H i Lyα absorption toward the F8 V star HD 35296. This line of sight is only a few degrees from the downwind direction of the local interstellar medium flow vector. As a consequence, Lyα absorption from the heliotail is detected in the spectrum, consistent with three previous downwind detections of heliotail absorption. The clustering of the heliotail absorption detections around the downwind direction demonstrates that the heliotail is pointed close to that direction, limiting the extent to which the interstellar magnetic field might be distorting and deflecting the heliotail. We explore this issue further using three-dimensional MHD models of the global heliosphere. The three computed models represent the first three-dimensional MHD models with both a kinetic treatment of neutrals and an extended grid in the tail direction, both of which are necessary to model Lyα absorption downwind. The models indicate only modest heliotail asymmetries and deflections, which are not large enough to be inconsistent with the clustering of heliotail absorption detections around the downwind direction. The models are reasonably successful at reproducing the observed absorption, but they do overpredict the Lyα opacity by a factor of 2–3. We discuss implications of these results in light of observations of the heliotail region from the Interstellar Boundary Explorer mission.

We propose a generalization of Becker's cloud model (BCM): an embedded cloud model (ECM)—for the inversion of the core of the Hα line spectrum of a plasma feature either lying high above the forest of chromospheric features or partly embedded in the outermost part of this forest. The fundamental assumption of the ECM is that the background light incident on the bottom of the feature from below is equal to the ensemble-average light at the same height. This light is related to the observed ensemble-average light via the radiative transfer that is described by the four parameters newly introduced in addition to the original four parameters of the BCM. Three of these new parameters are independently determined from the observed rms contrast profile of the ensemble. We use the constrained χ² fitting technique to determine the five free parameters. We find that the ECM leads to the fairly good fitting of the observed line profiles and the reasonable inference of physical parameters in quiet regions where the BCM cannot. Our first application of this model to a quiet region of the Sun indicates that the model can produce the complete velocity map and Doppler width map of the region.

We present Maxwellian-averaged effective collision strengths for the electron-impact excitation of S iii over a wide range of electron temperatures of astrophysical importance, log T_e(K) = 3.0–6.0. The calculation incorporates 53 fine-structure levels arising from the six configurations—3s²3p², 3s3p³, 3s²3p3d, 3s²3p4s, 3s²3p4p, and 3s²3p4d—giving rise to 1378 individual lines and is undertaken using the recently developed RMATRX II plus FINE95 suite of codes. A detailed comparison is made with a previous R-matrix calculation and significant differences are found for some transitions. The atomic data are subsequently incorporated into the modeling code cloudy to generate line intensities for a range of plasma parameters, with emphasis on allowed ultraviolet extreme-ultraviolet emission lines detected from the Io plasma torus. Electron density-sensitive line ratios are calculated with the present atomic data and compared with those from CHIANTI v7.1, as well as with Io plasma torus spectra obtained by Far-Ultraviolet Spectroscopic Explorer and Extreme-Ultraviolet Explorer. The present line intensities are found to agree well with the observational results and provide a noticeable improvement on the values predicted by CHIANTI.

Modern sky surveys are returning precision measurements of cosmological statistics such as weak lensing shear correlations, the distribution of galaxies, and cluster abundance. To fully exploit these observations, theorists must provide predictions that are at least as accurate as the measurements, as well as robust estimates of systematic errors that are inherent to the modeling process. In the nonlinear regime of structure formation, this challenge can only be overcome by developing a large-scale, multi-physics simulation capability covering a range of cosmological models and astrophysical processes. As a first step to achieving this goal, we have recently developed a prediction scheme for the matter power spectrum (a so-called emulator), accurate at the 1% level out to k ∼ 1 Mpc⁻¹ and z = 1 for wCDM cosmologies based on a set of high-accuracy N-body simulations. It is highly desirable to increase the range in both redshift and wavenumber and to extend the reach in cosmological parameter space. To make progress in this direction, while minimizing computational cost, we present a strategy that maximally reuses the original simulations. We demonstrate improvement over the original spatial dynamic range by an order of magnitude, reaching k ∼ 10 h Mpc⁻¹, a four-fold increase in redshift coverage, to z = 4, and now include the Hubble parameter as a new independent variable. To further the range in k and z, a new set of nested simulations run at modest cost is added to the original set. The extension in h is performed by including perturbation theory results within a multi-scale procedure for building the emulator. This economical methodology still gives excellent error control, ∼5% near the edges of the domain of applicability of the emulator. A public domain code for the new emulator is released as part of the work presented in this paper.

If the radio background is coming from cosmological sources, there should be some amount of clustering due to the large scale structure in the universe. Simple models for the expected clustering combined with the recent measurement by ARCADE-2 of the mean extragalactic temperature lead to predicted clustering levels that are substantially above upper limits from searches for anisotropy on arcminute scales using the Australia Telescope Compact Array and the Very Large Array. The rms temperature variations in the cosmic radio background appear to be more than a factor of 10 smaller (in temperature) than the fluctuations in the cosmic infrared background. It is therefore extremely unlikely that this background comes from galaxies, galaxy clusters, or any sources that trace dark matter halos at z ≲ 5, unless typical sources are smooth on arcminute scales, requiring typical sizes of several Mpc.