Table of contents

We present a homogeneous catalog of 275 large (effective radius ≳53) ultra-diffuse galaxy (UDG) candidates lying within an ≈290 square degree region surrounding the Coma Cluster. The catalog results from our automated postprocessing of data from the Legacy Surveys, a three-band imaging survey covering 14,000 square degrees of the extragalactic sky. We describe a pipeline that identifies UDGs and provides their basic parameters. The survey is as complete in these large UDGs as previously published UDG surveys of the central region of the Coma Cluster. We conclude that the majority of our detections are at roughly the distance of the Coma Cluster, implying effective radii ≥2.5 kpc, and that our sample contains a significant number of analogs of DF44, where the effective radius exceeds 4 kpc, both within the cluster and in the surrounding field. The g − z color of our UDGs spans a large range, suggesting that even large UDGs may reflect a range of formation histories. A majority of the UDGs are consistent with being lower stellar mass analogs of red sequence galaxies, but we find both red and blue UDG candidates in the vicinity of the Coma Cluster and a relative overabundance of blue UDG candidates in the lower-density environments and the field. Our eventual processing of the full Legacy Surveys data will produce the largest, most homogeneous sample of large UDGs.

The color distributions of globular clusters (GCs) in individual early-type galaxies show great diversity in their morphology. Based on the conventional "linear" relationship between the colors and metallicities of GCs, the GC metallicity distributions inferred from colors and in turn their formation histories, should be as diverse as they appear. In contrast, here we show that an alternative scenario rooted in the "nonlinear" nature of the metallicity-to-color transformation points to a simpler and more coherent picture. Our simulations of the color distributions for ∼80 GC systems in early-type galaxies from the ACS Virgo and Fornax Cluster Surveys suggest that the majority (∼70%) of early-type galaxies have old (∼13 Gyr) and coeval GCs. Their variety in the color distribution morphology stems mainly from one parameter, the mean metallicity of a GC system. Furthermore, the color distributions of the remaining (∼30%) GC systems are also explained by the nonlinearity scenario, assuming additional young or intermediate-age GCs with a number fraction of ∼20% of underlying old GCs. Our results reinforce the nonlinearity explanation for the GC color bimodality and provide a new perspective on early-type galaxy formation in the cluster environment, such as the Virgo and Fornax galaxy clusters.

When modeling and interpreting the spectral energy distributions (SEDs) of galaxies, the simple stellar population (SSP) model, star formation history (SFH), and dust attenuation law (DAL) are three of the most important components. However, each of them carries significant uncertainties that have seriously limited our ability to reliably recover the physical properties of galaxies from the analysis of their SEDs. In this paper, we present a Bayesian framework to deal with these uncertain components simultaneously. Based on the Bayesian evidence, a quantitative implement of the principle of Occam's razor, the method allows a more objective and quantitative discrimination among the different assumptions about these uncertain components. With a K_s-selected sample of 5467 low-redshift (mostly with z ≲ 1) galaxies in the COSMOS/UltraVISTA field and classified into passively evolving galaxies (PEGs) and star-forming galaxies (SFGs) with the UVJ diagram, we present a Bayesian discrimination of a set of 16 SSP models from five research groups (BC03 and CB07, M05, GALEV, Yunnan-II, BPASS V2.0), five forms of SFH (Burst, Constant, Exp-dec, Exp-inc, Delayed-τ), and four kinds of DAL (Calzetti law, MW, LMC, SMC). We show that the results obtained with the method are either obvious or understandable in the context of stellar/galaxy physics. We conclude that the Bayesian model comparison method, especially that for a sample of galaxies, is very useful for discriminating the different assumptions in the SED modeling of galaxies. The new version of the BayeSED code, which is used in this work, is publicly available at https://bitbucket.org/hanyk/bayesed/.

Spectra of hot methane were recorded using a tube furnace and a high-resolution Fourier transform spectrometer. We obtained experimental absorption spectra in the 1.85–1.11 μm near-infrared region at eight temperatures ranging from 295 K up to 1000 K. We have converted these into an atlas of absorption cross sections at each temperature for the methane tetradecad, icosad and triacontad polyads, excluding some spectral intervals either strongly contaminated by water or due to baseline fringes. On the theoretical side, the spectra were simulated from the ab initio-based Reims-Tomsk TheoReTS line list for the same experimental conditions. This line list has been constructed by global variational calculations from potential energy and dipole moment surfaces followed by empirical line position corrections deduced from previously published analyses. The comparisons showed very good overall agreement between observations and theory at high spectral resolution for the tetradecad and icosad and at medium or low resolution above this range. A full set of the theoretical absorption cross sections is also included. Detailed temperature dependence of the methane absorption enables the efficient method of remotely probing the temperature of distant astronomical objects based on a comparison of relative signals in carefully selected spectral intervals. This first combined experimental and theoretical easy-to-use cross-section library in the near-infrared should be of major interest for the interpretation of current and future astronomical observations up to a resolving power of 100,000–300,000 in the range 6400–7600 cm⁻¹ and a resolving power of 5000–10,000 in the higher wavenumber range up to 9000 cm⁻¹.

We present the ugriz-band Dark Energy Camera (DECam) plus 3.6 and 4.5 μm IRAC catalogs for the Spitzer/HETDEX Exploratory Large-Area (SHELA) survey. SHELA covers ∼24 deg² of the Sloan Digital Sky Survey (SDSS) "Stripe 82" region, with seven bandpasses spanning a wavelength range of 0.35 to 4.5 μm. SHELA falls within the footprint of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), which will provide spectroscopic redshifts for ∼200,000 Lyα emitters at 1.9 < z < 3.5 and also for ∼200,000 [O ii] emitters at z < 0.5. SHELA's deep, wide-area multiwavelength images, combined with HETDEX's spectroscopic information, will facilitate many extragalactic studies, including measuring the evolution of galaxy stellar mass, halo mass, and environment from 1.5 < z < 3.5. Here we present riz-band-selected ugriz-band DECam catalogs that reach a 5σ depth of ∼24.5 AB mag (for point sources with an aperture that encloses 70% of the total flux) and cover 17.5 deg² of the overall SHELA field. We validate our DECam catalog by comparison to the DECam Legacy Survey (DECaLS) DR5 and the Dark Energy Survey (DES) DR1. We perform IRAC forced photometry with The Tractor image modeling code to measure 3.6 and 4.5 μm fluxes for all objects within our DECam catalog. We demonstrate the utility of our catalog by computing galaxy number counts and estimating photometric redshifts. Our photometric redshifts recover the available $\left\langle z\right\rangle =0.33$ SDSS spectroscopic redshifts with a 1σ scatter in Δz/(1 + z) of 0.04.

We present Data Releases 4 and 5 of the quasar catalog from the quasar survey by the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST), which includes quasars observed between 2015 September and 2017 June. There are a total of 19,253 quasars identified by visual inspections of the spectra. Among them, 11,458 were independently discovered by LAMOST, in which 3296 were reported by the SDSS DR12 and DR14 quasar catalog after our survey began, while the remaining 8162 are new discoveries of LAMOST. We provide the emission line measurements for Hα, Hβ, Mg ii, and/or C iv for 18,100 quasars. Since LAMOST does not have absolute flux calibration information, we obtain the monochromatic continuum luminosities by fitting the SDSS photometric data using the quasar spectra, and then estimate the black hole masses. The catalog and spectra for these quasars are available online. This is the third installment in the series of LAMOST quasar surveys that has released spectra for ∼43,000 quasars to date. There are 24,772 independently discovered quasars, 17,128 of which are newly discovered. In addition to this great supplement to the new quasar discoveries, LAMOST has also provided a large database (overlapped with SDSS) for investigating quasar spectral variability and discovering unusual quasars, including changing-look quasars, with ongoing and upcoming large surveys.

Microwave plasmas with H₂ and H₂/rare gas mixtures are convenient sources of VUV radiation for laboratory simulations of astrophysical media. We recently undertook an extensive study to characterize microwave plasmas in an H₂/He gas mixture in order to optimize a VUV solar simulator over the 115–170 nm spectral range. In this paper, we extend our investigation to the effect of the addition of Ar into H₂/He plasma on the VUV spectral irradiance. Our study combines various optical diagnostics such as a VUV spectrometer and optical emission spectroscopy. Quantitative measurements of the spectral irradiance and photons flux in different mixtures are accomplished using a combination of VUV spectrometry and chemical actinometry. Results show that the Ar addition into H₂/He plasma largely affects the predominant emissions of the hydrogen Lyα line (121.6 nm) and H₂ (B¹Σ_u–X¹Σ_g) band (150–170 nm). While a microwave plasma with 1.4% H₂/He is required to mimic the entire VUV solar spectrum in the 115–170 nm range, the combination with 1.28% H₂/35% Ar/He is the best alternative to obtain a quasi-monochromatic spectrum with emission dominated by the Lyα line. The maximum of the spectral irradiance is significantly higher in the ternary mixtures compared to the binary mixture of 1.4% H₂/He. Further Ar increase yielded lower spectral irradiance and absolute photon fluxes. Our measured spectral irradiances are compared to VUV solar data in the 115–170 nm range, emphasizing the use of microwave plasmas in astrophysical studies and laboratory simulations of planetary atmospheres.

In this work we present a proof of concept of CUDA-capable, resistive, multi-fluid models of relativistic magnetohydrodynamics (RMHD). Resistive and multi-fluid codes for simulating models of RMHD suffer from stiff source terms, so it is common to implement a set of semi-implicit time integrators to maintain numerical stability. We show, for the first time, that finite volume IMEX schemes for resistive and two-fluid models of RMHD can be accelerated by execution on graphics processing units, significantly reducing the demand set by these kinds of problems. We report parallel speed-ups of over 21× using double-precision floating-point accuracy, and highlight the optimization strategies required for these schemes, and how they differ from ideal RMHD models. The impact of these results is discussed in the context of the next-generation simulations of neutron star mergers.

The Milky Way Imaging Scroll Painting project is an unbiased Galactic plane CO survey for mapping regions of $l=-10^\circ$ to +250° and $| b| \,\lesssim$ 52 with the 13.7 m telescope of the Purple Mountain Observatory. The legacy survey aims to observe the ${}^{12}\mathrm{CO}$, ${}^{13}\mathrm{CO}$, and C¹⁸O (J = 1–0) lines simultaneously with full-sampling using the nine-beam Superconducting SpectroScopic Array Receiver system with an instantaneous bandwidth of 1 GHz. In this paper, the completed 250 deg² data from l = +258 to +497 are presented with a grid spacing of 30'' and a typical rms noise level of ∼0.5 K for ${}^{12}\mathrm{CO}$ at the channel width of 0.16 km $\,{{\rm{s}}}^{-1}$ and ∼0.3 K for ${}^{13}\mathrm{CO}$ and C¹⁸O at 0.17 km $\,{{\rm{s}}}^{-1}$. The high-quality data, with moderate resolution (∼50''), uniform sensitivity, and high spatial dynamic range, allow us to investigate the details of molecular clouds (MCs) traced by the three CO isotope lines. Three interesting examples are briefly investigated, including distant Galactic spiral arms traced by CO emission with V_LSR < 0 km s⁻¹, the bubble-like dense gas structure near the H ii region W40, and the MCs distribution perpendicular to the Galactic plane.

We present an empirical stellar spectra library created using spectra from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) DR5. This library represents a uniform data set ranging from 3750 through 8500 K in effective temperature (T_eff), from −2.5 through +1.0 dex in metallicity ([Fe/H]), and from 0 to 5.0 dex in gravity (log g). The spectra in the library have resolutions R ∼ 1800, with well-calibrated fluxes and rest-framed wavelengths. Using a large number of red stars observed by LAMOST, we generated denser K-type templates to fill in data missing from current empirical spectral libraries, particularly the late K type. For K giants, we calibrated the spectroscopic surface gravities against the asteroseismic surface gravities. To verify the reliability of the parameters labeled for this library, we performed an internal cross-validation using a χ² minimization method to interpolate the parameters of each individual spectrum using the remaining spectra in the library. We obtained precisions of 41 K, 0.11 dex, and 0.05 dex for T_eff, log g, and [Fe/H], respectively, which means the templates are labeled with correct stellar parameters. Through external comparisons, we confirmed that measurements of the stellar parameters through this library can achieve accuracies of approximately 125 K in T_eff, 0.1 dex in [Fe/H] and 0.20 dex in log g without systematic offset. This empirical library is useful for stellar parameter measurements because it has large parameter coverage and full wavelength coverage from 3800 to 8900 Å.

During major solar flares, the photospheric magnetic field of the flaring active region is often observed to change abruptly, permanently, and significantly. Here we analyze vector magnetograms covering 15 X-class flares observed in 11 active regions by the Solar Dynamic Observatory Helioseismic and Magnetic Imager. Resolving magnetic changes using a reference potential field, more complex magnetic field, Lorentz force, and magnetic shear changes could be analyzed than previously. In each case, physical and coherent patterns of change were found. Generally the dominant change was in the horizontal field component that strengthened in the central structure, accompanied there by a downward Lorentz force change and strengthening of horizontal magnetic shear consistent with magnetic implosion, with weaker changes of opposite sign in neighboring and peripheral regions including sunspots. In most cases this central structure was a strong, sheared photospheric magnetic neutral line, but in one case it was an isolated unipolar sunspot. Magnetic relaxation in the vertical direction was typical throughout the flaring regions. Unique in this study was the behavior at bald-patch structures during the X-class flares of 2017 September 6 in NOAA Active Region 12673. During the X9.3 flare, the horizontal and vertical field components weakened and the shear relaxed in horizontal and vertical directions, indicating a large free magnetic energy source for the flare. The magnetic changes at the bald patches exhibited evidence of organized vertical magnetic flux reduction during three X-class flares, not found at other structures, suggesting the greater possibilities of magnetic reconfiguration and energy release at bald patches.

We present a single-dish mapping algorithm with a number of advantages over traditional techniques. (1) Our algorithm makes use of weighted modeling, instead of weighted averaging, to interpolate between signal measurements. This smooths the data, but without blurring the data beyond instrumental resolution. Techniques that rely on weighted averaging blur point sources sometimes by as much as 40%. (2) Our algorithm makes use of local, instead of global, modeling to separate astronomical signal from instrumental and/or environmental signal drift along the telescope's scans. Other techniques, such as basket weaving, model this drift with simple functional forms (linear, quadratic, etc.) across the entirety of scans, limiting their ability to remove such contaminants. (3) Our algorithm makes use of a similar, local modeling technique to separate astronomical signal from radio-frequency interference (RFI), even if only continuum data are available. (4) Unlike other techniques, our algorithm does not require data to be collected on a rectangular grid or regridded before processing. (5) Data from any number of observations, overlapping or not, may be appended and processed together. (6) Any pixel density may be selected for the final image. We present our algorithm and evaluate it using both simulated and real data. We are integrating it into the image-processing library of the Skynet Robotic Telescope Network, which includes optical telescopes spanning four continents, and now also Green Bank Observatory's 20 m diameter radio telescope in West Virginia. Skynet serves hundreds of professional users, and additionally tens of thousands of students, of all ages. Default data products are generated on the fly, but will soon be customizable after the fact.

We present the discovery of KELT-22Ab, a hot Jupiter from the KELT-South survey. KELT-22Ab transits the moderately bright (V ∼ 11.1) Sun-like G2V star TYC 7518-468-1. The planet has an orbital period of $P\,=1.3866529\pm 0.0000027$ days, a radius of ${R}_{P}={1.285}_{-0.071}^{+0.12}\,{R}_{J}$, and a relatively large mass of ${M}_{P}={3.47}_{-0.14}^{+0.15}\,{M}_{J}$. The star has ${R}_{\star }={1.099}_{-0.046}^{+0.079}\,{R}_{\odot }$, ${M}_{\star }={1.092}_{-0.041}^{+0.045}\,{M}_{\odot }$, ${T}_{\mathrm{eff}}\,={5767}_{-49}^{+50}$ K, $\mathrm{log}{g}_{\star }={4.393}_{-0.060}^{+0.039}$ (cgs), and [m/H] = $+{0.259}_{-0.083}^{+0.085}$; thus other than its slightly super-solar metallicity, it appears to be a near-solar twin. Surprisingly, KELT-22A exhibits kinematics and a Galactic orbit that are somewhat atypical for thin-disk stars. Nevertheless, the star is rotating rapidly for its estimated age, and shows evidence of chromospheric activity. Imaging reveals a slightly fainter companion to KELT-22A that is likely bound, with a projected separation of 6''  (∼1400 au). In addition to the orbital motion caused by the transiting planet, we detect a possible linear trend in the radial velocity of KELT-22A, suggesting the presence of another relatively nearby body that is perhaps non-stellar. KELT-22Ab is highly irradiated (as a consequence of the small semimajor axis of $a/{R}_{\star }=4.97$), and is mildly inflated. At such small separations, tidal forces become significant. The configuration of this system is optimal for measuring the rate of tidal dissipation within the host star. Our models predict that, due to tidal forces, the semimajor axis is decreasing rapidly, and KELT-22Ab is predicted to spiral into the star within the next Gyr.

The Survey of Ionized Gas of the Galaxy, Made with the Arecibo telescope (SIGGMA) provides a fully sampled view of the radio recombination line (RRL) emission from the portion of the Galactic plane visible with Arecibo. Observations use the Arecibo L-band Feed Array, which has a FWHM beam size of 34. Twelve hydrogen RRLs from H163α to H174α are located within the instantaneous bandpass from 1225 MHz to 1525 MHz. We provide here cubes of average ("stacked") RRL emission for the inner Galaxy region 32° ≤ ℓ ≤ 70°, $| b| \leqslant 1\buildrel{\circ}\over{.} 5$, with an angular resolution of 6'. The stacked RRL rms at 5.1 km s⁻¹ velocity resolution is ∼0.65 mJy beam⁻¹, making this the most sensitive large-scale fully sampled RRL survey extant. We use SIGGMA data to catalog 319 RRL detections in the direction of 244 known H ii regions, and 108 new detections in the direction of 79 H ii region candidates. We identify 11 carbon RRL emission regions, all of which are spatially coincident with known H ii regions. We detect RRL emission in the direction of 14 of the 32 supernova remnants (SNRs) found in the survey area. This RRL emission frequently has the same morphology as the SNRs. The RRL velocities give kinematic distances in agreement with those found in the literature, indicating that RRLs may provide an additional tool to constrain distances to SNRs. Finally, we analyze the two bright star-forming complexes: W49 and W51. We discuss the possible origins of the RRL emission in directions of SNRs W49B and W51C.

A small survey of the UV-absorbing gas in 12 low-z galaxy groups has been conducted using the Cosmic Origins Spectrograph on board the Hubble Space Telescope. Targets were selected from a large, homogeneously selected sample of groups found in the Sloan Digital Sky Survey. A critical selection criterion excluded sight lines that pass close (<1.5 virial radii) to a group galaxy, to ensure absorber association with the group as a whole. Deeper galaxy redshift observations are used both to search for closer galaxies and also to characterize these 10^13.5–10^14.5M_⊙ groups, the most massive of which are highly virialized with numerous early-type galaxies (ETGs). This sample also includes two spiral-rich groups, not yet fully virialized. At group-centric impact parameters of 0.3–2 Mpc, these signal-to-noise ratios = 15–30 spectra detected H i absorption in 7 of 12 groups; high (O vi) and low (Si iii) ion metal lines are present in two-thirds of the absorption components. None of the three most highly virialized, ETG-dominated groups are detected in absorption. Covering fractions ≳50% are seen at all impact parameters probed, but do not require large filling factors despite an enormous extent. Unlike halo clouds in individual galaxies, group absorbers have radial velocities that are too low to escape the group potential well without doubt. This suggests that these groups are "closed boxes" for galactic evolution in the current epoch. Evidence is presented that the cool and warm group absorbers are not a pervasive intra-group medium (IGrM), requiring a hotter (T ∼ 10⁶–10⁷ K) IGrM to be present to close the baryon accounting.