Low Mass Group Environments have no Substantial Impact on the Circumgalactic Medium Metallicity

We explore how environment affects the metallicity of the circumgalactic medium (CGM) using 13 low mass galaxy groups (2-5 galaxies) at $\langle z_{abs}\rangle=0.25$ identified near background quasars. Using quasar spectra from HST/COS and from Keck/HIRES or VLT/UVES we measure column densities of, or determine limits on, CGM absorption lines. We use a Markov chain Monte Carlo approach with Cloudy to estimate metallicities of cool ($T\sim10^4$K) CGM gas within groups and compare them to CGM metallicities of 47 isolated galaxies. Both group and isolated CGM metallicities span a wide range ($-2<$[Si/H]$<0$), where the mean group ($-0.54\pm0.22$) and isolated ($-0.77\pm0.14$) CGM metallicities are similar. Group and isolated environments have similar distributions of {\HI} column densities as a function of impact parameter. However, contrary to isolated galaxies, we do not find an anti-correlation between {\HI} column density and the nearest group galaxy impact parameter. We additionally divided the groups by member luminosity ratios (i.e., galaxy-galaxy and galaxy-dwarf groups). While there was no significant difference in their mean metallicities, a modest increase in sample size should allow one to statistically identify a higher CGM metallicity in galaxy-dwarf groups compared to galaxy-galaxy groups. We conclude that either environmental effects have not played an important role in the metallicity of the CGM at this stage and expect that this may only occur when galaxies are strongly interacting or merging, or that some isolated galaxies have higher CGM metallicities due to past interactions. Thus, environment does not seem to be the cause of the CGM metallicity bimodality.Comment: 14 pages, 5 figures, 2 figure sets, 1 machine-readable tabl

Exploratory Study of the X-Ray Properties of Quasars With Intrinsic Narrow Absorption Lines

We have used archival Chandra and XMM-Newton observations of quasars hosting intrinsic narrow UV absorption lines (intrinsic NALs) to carry out an exploratory survey of their X-ray properties. Our sample consists of three intrinsic-NAL quasars and one "mini-BAL" quasar, plus four quasars without intrinsic absorption lines for comparison. These were drawn in a systematic manner from an optical/UV-selected sample. The X-ray properties of intrinsic-NAL quasars are indistinguishable from those of "normal" quasars. We do not find any excess absorption in quasars with intrinsic NALs, with upper limits of a few times 10^22 cm^-2. We compare the X-ray and UV properties of our sample quasars by plotting the equivalent width and blueshift velocity of the intrinsic NALs and the X-ray spectral index against the "optical-to-X-ray" slope, alpha-ox. When BAL quasars and other AGNs with intrinsic NALs are included, the plots suggest that intrinsic-NAL quasars form an extension of the BAL sequences and tend to bridge the gap between BAL and "normal" quasars. Observations of larger samples of intrinsic-NAL quasars are needed to verify these conclusions. We also test two competing scenarios for the location of the NAL gas in an accretion-disk wind. Our results strongly support a location of the NAL gas at high latitudes above the disk, closer to the disk axis than the dense BAL wind. We detect excess X-ray absorption only in Q0014+8118, which does not host intrinsic NALs. The absorbing medium very likely corresponds to an intervening system at z=1.1, which also produces strong absorption lines in the rest-frame UV spectrum of this quasar. In the appendix we discuss the connection between UV and X-ray attenuation and its effect on alpha-ox.Comment: Accepted by the Astrophysical Journa

Probing Lyman-alpha Absorbers in Cosmological Simulations with Double Lines of Sight

We perform a double line of sight (DLOS) analysis of the Lyman-alpha forest structures that form and evolve in cosmological N-body/hydrodynamic simulations. Pairs of simulated spectra, extracted from lines of sight separated by distances from D=12.5kpc up to 800kpc, and a ``control sample'' of unrelated lines of sight, are analyzed at redshifts 3, 2, and 1. Coincident line samples are defined for HI column density thresholds of Nco = 10^{12.5}, 10^{13}, and 10^{14} per square cm. We find that: 1) Under the assumption of a single structure size, a Bayesian analysis yields sizes that are larger for smaller Nco, and at fixed Nco the size decreases with decreasing redshift. However, these derived sizes are found to increase with increasing D indicating that the assumption of a single structure size is invalid. 2) The column densities of coincident pairs are highly correlated for small D, with increasing scatter as D is increased, consistent with structures that have a centrally peaked N(HI) that decreases gradually with radius. 3) The velocity difference distribution for coincident lines is very narrow for small D, and widens as D is increased to meet the expectation for chance coincidences in unrelated lines of sight. This behavior is indicative of organized motion within the structures. 4) For small D, the distribution of anticoincident line column densities, Nac, falls steeply as Nac increases from the cutoff value, but has a significant tail at large values which is inconsistent with a population of spherical absorbers with sharp edges, and consistent with a flattened geometry. The conclusions reached on the basis of the DLOS analysis are validated by an examination of the three-dimensional structures and velocity flows in the simulation data.Comment: 17 pages, Latex file, and 8 PostScript figures; Submitted to the Astrophysical Journal; Available as a single compressed Postscript file at http://www.astro.psu.edu/users/charlto

A Complex Multiphase DLA Associated with a Compact Group at z=2.431 Traces Accretion, Outflows, and Tidal Streams

As part of our program to identify host galaxies of known z=2-3 MgII absorbers with the Keck Cosmic Web Imager (KCWI), we discovered a compact group giving rise to a z=2.431 DLA with ultra-strong MgII absorption in quasar field J234628+124859. The group consists of four star-forming galaxies within 8-28 kpc and $v\sim40-340$ km s$^{-1}$ of each other, where tidal streams are weakly visible in deep HST imaging. The group geometric centre is D=25 kpc from the quasar (D=20-40 kpc for each galaxy). Galaxy G1 dominates the group ($1.66L_{\ast}$, ${\rm SFR}_{\rm FUV}=11.6$ M$_{\odot}$ yr$^{-1}$) while G2, G3, and G4 are less massive ($0.1-0.3L_{\ast}$, ${\rm SFR}_{\rm FUV}=1.4-2.0$ M$_{\odot}$ yr$^{-1}$). Using a VLT/UVES quasar spectrum covering the HI Lyman series and metal lines such as MgII, SiIII, and CIV, we characterised the kinematic structure and physical conditions along the line-of-sight with cloud-by-cloud multiphase Bayesian modelling. The absorption system has a total $\log(N(HI)/{\rm cm}^{-2})=20.53$ and an $N(HI)$-weighted mean metallicity of $\log(Z/Z_{\odot})=-0.68$, with a very large MgII linewidth of $\Delta v\sim700$ km s$^{-1}$. The highly kinematically complex profile is well-modelled with 30 clouds across low and intermediate ionisation phases with values ${13\lesssim\log(N(HI)/{\rm cm}^{-2})\lesssim20}$ and $-3\lesssim\log(Z/Z_{\odot})\lesssim1$. Comparing these properties to the galaxy properties, we infer a wide range of gaseous environments, including metal-rich outflows, metal-poor IGM accretion, and tidal streams from galaxy--galaxy interactions. This diversity of structures forms the intragroup medium around a complex compact group environment at the epoch of peak star formation activity. Surveys of low redshift compact groups would benefit from obtaining a more complete census of this medium for characterising evolutionary pathways.Comment: 29 pages, 10 figures. Accepted for publication in MNRAS 28 June 202

Relationship between the Metallicity of the Circumgalactic Medium and Galaxy Orientation

We investigate the geometric distribution of gas metallicities in the circumgalactic medium (CGM) around $47$, $z<0.7$ galaxies from the "Multiphase Galaxy Halos" Survey. Using a combination of quasar spectra from HST/COS and from Keck/HIRES or VLT/UVES we measure column densities of, or determine limits on, CGM absorption lines. We then use a Monte-Carlo Markov chain approach with Cloudy to estimate the metallicity of cool (T$\sim$$10^4$K) CGM gas. We also use HST images to determine host galaxy inclination and quasar--galaxy azimuthal angles. Our sample spans a HI column density range of $13.8$ cm s$^{-1}<{\log N_{HI}}<19.9$ cm s$^{-1}$. We find (1) while the metallicity distribution appears bimodal, a Hartigan dip test cannot rule out a unimodal distribution ($0.4\sigma$). (2) CGM metallicities are independent of halo mass, spanning three orders of magnitude at fixed halo mass. (3) The CGM metallicity does not depend on the galaxy azimuthal and inclination angles regardless of HI column density, impact parameter and galaxy color. (4) Ionization parameter does not depend on azimuthal angle. We suggest that the partial Lyman limit metallicity bimodality is not driven by a spatial azimuthal bimodality. Our results are consistent with simulations where the CGM is complex and outflowing, accreting, and recycled gas are well-homogenized at $z<0.7$. The presence of low metallicity gas at all orientations suggests that cold streams of accreting filaments are not necessarily aligned with the galaxy plane at low redshifts or intergalactic transfer may dominate. Finally, our results support simulations showing that strong metal absorption can mask the presence of low metallicity gas in integrated line-of-sight CGM metallicities.Comment: 87 pages, 22 pages of main text, 65 pages of appendices, 106 figures and 50 tables. Accepted for publication in ApJ 31 July 201

The Diagnosis and Management of Nonalcoholic Fatty Liver Disease: Practice Guidance from the American Association for the Study of Liver Diseases

This guidance provides a data-supported approach to the diagnostic, therapeutic, and preventive aspects of NAFLD care. A “Guidance” document is different from a “Guideline.” Guidelines are developed by a multidisciplinary panel of experts and rate the quality (level) of the evidence and the strength of each recommendation using the Grading of Recommendations, Assessment Development, and Evaluation (GRADE) system. A guidance document is developed by a panel of experts in the topic, and guidance statements, not recommendations, are put forward to help clinicians understand and implement the most recent evidence