Search

The multiphase circumgalactic medium (CGM) hosts critical processes that affect galaxy evolution such as accretion and outflows. We searched for evidence of these phenomena by using the EW co-rotation fraction (⁠|$f_{\rm EWcorot}$|⁠) to study the kinematic connection between the multiphase CGM and host galaxy rotation. We examined CGM absorption from Hubble Space Telescope / Cosmic Origins Spectrograph (including, but not limited to, Si  ii , C  ii , Si  iii , C  iii , and O  vi) within |$21\le D\le ~276$| kpc of 27 galaxies. We find the median |$f_{\rm EWcorot}$| for all ions is consistent within errors and the |$f_{\rm EWcorot}$| increases with increasing N |$({{{\rm H} \rm{\small I}}})$|⁠. The |$f_{\rm EWcorot}$| of lower ionization gas decreases with increasing |$D/R_{\rm vir}$|⁠ , while O  vi and H  i are consistent with being flat. The |$f_{\rm EWcorot}$| varies minimally as a function of azimuthal angle and is similar for all ions at a fixed azimuthal angle. The larger number of O  vi detections enabled us to investigate where the majority of co-rotating gas is found. Highly co-rotating O  vi primarily resides along the galaxies' major axis. Looking at the |$f_{\rm EWcorot}$| as a function of ionization potential (⁠|${{\rm d}{({f_{\rm EWcorot}})}}/{{\rm d}{(\rm eV)}}$|⁠), we find a stronger co-rotation signature for lower ionization gas. There are suggestions of a connection between the CGM metallicity and major axis co-rotation where low-ionization gas with higher |$f_{\rm EWcorot}$| exhibits lower metallicity and may trace large-scale filamentary inflows. Higher ionization gas with higher |$f_{\rm EWcorot}$| exhibits higher metallicity and may instead trace co-planar recycled gas accretion. Our results stress the importance of comparing absorption originating from a range of ionization phases to differentiate between various gas flow scenarios. [ABSTRACT FROM AUTHOR]

The circumgalactic medium (CGM) hosts many physical processes with different kinematic signatures that affect galaxy evolution. We address the CGM–galaxy kinematic connection by quantifying the fraction of H  i that is aligned with galaxy rotation with the equivalent width co-rotation fraction, |$f_{\rm EWcorot}$|⁠. Using 70 quasar sightlines having Hubble Space Telescope /Cosmic Origins Spectrograph H  i absorption (⁠|${12\lt \log (N(\rm{{\rm H}\,{\small I}})/{\rm cm}^{-2})\lt 20}$|⁠) within |$5R_{\rm vir}$| of |$z\lt 0.6$| galaxies we find that |$f_{\rm EWcorot}$| increases with increasing H  i column density. |$f_{\rm EWcorot}$| is flat at |$\sim 0.6$| within |$R_{\rm vir}$| and decreases beyond |$R_{\rm vir}$| to |$f_{\rm EWcorot}$| |$\sim 0.35$|⁠. |$f_{\rm EWcorot}$| also has a flat distribution with azimuthal and inclination angles within |$R_{\rm vir}$|⁠ , but decreases by a factor of two outside of |$R_{\rm vir}$| for minor axis gas and by a factor of 2 for edge-on galaxies. Inside |$R_{\rm vir}$|⁠ , co-rotation dominated H i is located within |$\sim 20$| deg of the major and minor axes. We surprisingly find equal amounts of H  i absorption consistent with co-rotation along both major and minor axes within |$R_{\rm vir}$|⁠. However, this co-rotation disappears along the minor axis beyond |$R_{\rm vir}$|⁠ , suggesting that if this gas is from outflows, then it is bound to galaxies. |$f_{\rm EWcorot}$| is constant over two decades of halo mass, with no decrease for log(M |$_{\rm h}/{\rm M}_{\odot })\gt 12$| as expected from simulations. Our results suggest that co-rotating gas flows are best found by searching for higher column density gas within |$R_{\rm vir}$| and near the major and minor axes. [ABSTRACT FROM AUTHOR]

The pervasive presence of warm gas in galaxy haloes suggests that the circumgalactic medium (CGM) is multiphase in its ionization structure and complex in its kinematics. Some recent state-of-the-art cosmological galaxy simulations predict an azimuthal dependence of CGM metallicities. We investigate the presence of such a trend by analysing the distribution of gas properties in the CGM around 47 z < 0.7 galaxies from the Multiphase Galaxy Halos Survey determined using a cloud-by-cloud, multiphase, ionization modelling approach. We identify three distinct populations of absorbers: cool clouds (T ∼ 104.1 K) in photoionization equilibrium, warm–hot collisionally ionized clouds (T ∼ 104.5–105 K) affected by time-dependent photoionization, and hotter clouds (T ∼ 105.4–106 K) with broad O  vi and Ly α absorption consistent with collisional ionization. We find that fragmentation can play a role in the origin of cool clouds, that warm–hot clouds are out of equilibrium due to rapid cooling, and that hotter clouds are representative of virialized halo gas in all but the lowest mass galaxies. The metallicities of clouds do not depend on the azimuthal angle or other galaxy properties for any of these populations. At face value, this disagrees with the simplistic model of the CGM with bipolar outflows and cold-mode planar accretion. However, the number of clouds per sightline is significantly larger close to the minor and major axes. This implies that the processes of outflows and accretion are contributing to these CGM cloud populations, and our sightlines are probing gas of mixed origins at all azimuthal angles in these low-redshift galaxies. [ABSTRACT FROM AUTHOR]

This reprint of an article on the experiences of two mathematically precocious youths is preceded by a commentary that stresses the increased zest for learning experienced by the accelerants, the benefits of better educational preparation, and the importance of parental support for acceleration. (Contains 9 references.) (CR)

This article provides information about educational and career outcomes of 12 youths, identified in the Study of Mathematically Precocious Youth and Center for Talented Youth, who received rapid educational acceleration. Also, three young adults who were accelerated share their experiences, concluding that such advancement was optimal for them but may not be the ideal path for others. (JDD)

We present here results from a survey of intervening C  iv absorbers at z < 0.16 conducted using 223 sightlines from the Hubble Spectroscopic Legacy Archive. Most systems (83%) out of the total sample of 69 have simple kinematics with 1 or 2 C  iv components. In the 22 C  iv systems with well constrained H  i column densities, the temperatures from the b -values imply predominantly photoionized plasma (T ≤ 105 K) and non-thermal dynamics. These systems also have solar or higher metallicities. We obtain a C  iv line density of |$\mathrm{ d}\mathcal {N}/\mathrm{ d}X = 5.1\pm 1.0$| for |$\log [N(\rm {C}\, \rm {{iv}})~(\rm {cm}^{-2})]\ge 12.9$|⁠ , and |$\Omega _{\rm {C}\, \rm {\rm {iv}}}=(8.01\pm 1.62) \times 10^{-8}$| for |$12.9 \le \log [N(\rm {C}\, \rm {{iv}})~(\rm {cm}^{-2})] \le 15.0$|⁠. The C  iv bearing diffuse gas in the z < 0.16 Universe has a metallicity of (2.07  ±  0.43) ×  10−3 Z⊙, an order of magnitude more than the metal abundances in the IGM at high redshifts (z ≳ 5), and consistent with the slow build-up of metals in the diffuse circum/intergalactic space with cosmic time. For z < 0.015 (complete above L > 0.01 L ⋆), the Sloan Digital Sky Survey provides a tentative evidence of declining covering fraction for strong C  iv (N > 1013.5 cm−2) with ρ (impact parameter) and ρ/ R vir. However, the increase at high separations suggests that strong systems are not necessarily coincident with such galaxies. We also find that strong C  iv absorption at z < 0.051 is not coincident with galaxy overdense regions complete for L > 0.13 L ⋆. [ABSTRACT FROM AUTHOR]

We present analysis of the galaxy environment and physical properties of a partial Lyman limit system at z  = 0.83718 with H  i and metal-line components closely separated in redshift space (|Δ v | ≈ 400 km s−1) towards the background quasar HE 1003 + 0149. The HST /COS far-ultraviolet spectrum provides coverage of lines of oxygen ions from O  i to O  v. Comparison of observed spectral lines with synthetic profiles generated from Bayesian ionization modelling reveals the presence of two distinct gas phases in the absorbing medium. The low-ionization phase of the absorber has sub-solar metallicities (∼1/10 solar) with indications of [C/O] <0 in each of three components. The O  iv and O  v trace a more diffuse higher ionization medium with predicted H  i column densities that are ≈2 dex lower. The quasar field observed with VLT /MUSE reveals three dwarf galaxies with stellar masses of M * ∼ 108–109 M⊙, and with star formation rates of ≈0.5–1 M⊙ yr−1, at projected separations of ρ/ R vir ≈ 1.8–3.0 from the absorber. Over a wider field with projected proper separation of ≤5 Mpc and radial velocity offset of |Δ v | ≤ 1000 km s−1 from the absorber, 21 more galaxies are identified in the VLT /VIMOS and Magellan deep galaxy redshift surveys, with 8 of them within 1 Mpc and 500 km s−1, consistent with the line of sight penetrating a group of galaxies. The absorber presumably traces multiple phases of cool (T ∼ 104 K) photoionized intragroup medium. The inferred [C/O] <0 hint at preferential enrichment from core-collapse supernovae, with such gas displaced from one or more of the nearby galaxies, and confined to the group medium. [ABSTRACT FROM AUTHOR]

We present a new method aimed at improving the efficiency of component by component ionization modelling of intervening quasar absorption-line systems. We carry out cloud-by-cloud, multiphase modelling making use of cloudy and Bayesian methods to extract physical properties from an ensemble of absorption profiles. Here, as a demonstration of method, we focus on four weak, low-ionization absorbers at low redshift, because they are multiphase but relatively simple to constrain. We place errors on the inferred metallicities and ionization parameters for individual clouds, and show that the values differ from component to component across the absorption profile. Our method requires user input on the number of phases and relies on an optimized transition for each phase, one observed with high resolution and signal-to-noise ratio. The measured Doppler parameter of the optimized transition provides a constraint on the Doppler parameter of H  i , thus providing leverage in metallicity measurements even when hydrogen lines are saturated. We present several tests of our methodology, demonstrating that we can recover the input parameters from simulated profiles. We also consider how our model results are affected by which radiative transitions are covered by observations (for example, how many H  i transitions) and by uncertainties in the b parameters of optimized transitions. We discuss the successes and limitations of the method, and consider its potential for large statistical studies. This improved methodology will help to establish direct connections between the diverse properties derived from characterizing the absorbers and the multiple physical processes at play in the circumgalactic medium. [ABSTRACT FROM AUTHOR]

We use adaptive mesh refinement cosmological simulations to study the spatial distribution and covering fraction of absorption in the circumgalactic medium (CGM) as a function of projected virial radius and azimuthal angle. We compare these simulations to an observed sample of 53 galaxies from the Multiphase Galaxy Halos Survey. Using Mockspec , an absorption-line analysis pipeline, we generate synthetic quasar absorption-line observations of the simulated CGM. To best emulate observations, we studied the averaged properties of 15,000 "mock samples," each of 53 sight lines having a distribution of and sight-line orientation statistically consistent with the observations. We find that the covering fraction obtained for the simulated galaxies agrees well with the observed value for the inner halo () and is within 1.1σ in the outer halo (), but is underproduced within. The observed bimodal distribution of the covering fraction with azimuthal angle, showing a higher frequency of absorption along the projected major and minor axes of galaxies, is not reproduced in the simulations. Further analysis reveals the spatial-kinematic distribution of -absorbing gas is dominated by outflows in the inner halo mixed with an inflowing gas that originates from farther out in the halo. Though the CGM of the individual simulated galaxies exhibits spatial structure, the flat azimuthal distribution occurs because the individual simulated galaxies do not develop a CGM structure that is universal from galaxy to galaxy. [ABSTRACT FROM AUTHOR]

The relationship between a galaxy's properties and its circumgalactic medium (CGM) provides a unique view of how galaxies evolve. We present an interesting edge-on (i = 86°) disc galaxy (G1547) where the CGM is probed by a background quasar at a distance of 84 kpc and within 10° of the galaxy major axis. G1547 does not have any detectable CGM absorption down to stringent limits, covering H  i (EW r  <0.02 Å, log(N(H  i)/cm−2) < 12.6) and a range of low and high ionization absorption lines (O  i , C  ii , N  ii , Si  ii , C  iii , N  iii , Si  iii , C  iv , Si  iv , N  v , and O  vi). This system is rare, given the covering fraction of |$1.00_{-0.04}^{+0.00}$| for sub-L* galaxies within 50–100 kpc of quasar sightlines. G1547 has a low star formation rate (SFR, 1.1 M⊙ yr−1), specific SFR (sSFR, 1.5 × 10−10 yr−1), and ΣSFR (0.06 M⊙ yr−1 kpc−2) and does not exhibit active galactic nucleus or star-formation-driven outflows. Compared to the general population of galaxies, G1547 is in the green valley and has an above average metallicity with a negative gradient. When compared to other H  i absorption-selected galaxies, we find that quiescent galaxies with log(sSFR/yr−1) < −11 have a low probability (4/12) of possessing detectable H  i in their CGM, while all galaxies (40/40) with log(sSFR/yr−1) > −11 have H  i absorption. We conclude that sSFR is a good indicator of the presence of H  i CGM. Interestingly however, G1547 is the only galaxy with log(sSFR/yr−1) > −11 that has no detectable CGM. Given the properties of G1547, and its absent CGM, it is plausible that G1547 is undergoing quenching due to a lack of accreting fuel for star formation, with an estimated quenching time-scale of 4 ± 1 Gyr. G1547 provides a unique perspective into the external mechanisms that could explain the migration of galaxies into the green valley. [ABSTRACT FROM AUTHOR]

We present the detection and analysis of a weak low-ionization absorber at z  = 0.121 22 along the sightline of the blazar PG 1424+240, using spectroscopic data from both HST /COS and STIS. The absorber is a weak Mg  ii analogue, with an incidence of weak C  ii and Si  ii , along with multicomponent C  iv and O  vi. The low ions are tracing a dense (n H ∼ 10−3 cm−3) parsec-scale cloud of solar or higher metallicity. The kinematically coincident higher ions are either from a more diffuse (n H ∼ 10−5–10−4 cm−3) photoionized phase of kiloparsec-scale dimensions or are tracing a warm (T  ∼ 2 × 105 K) collisionally ionized transition temperature plasma layer. The absorber resides in a galaxy overdense region, with 18 luminous (> L *) galaxies within a projected radius of 5 Mpc and velocity of 750 km s−1. The multiphase properties, high metallicity, and proximity to a 1.4 L * galaxy, at ρ  ∼ 200 kpc and separation |Δ v | = 11 km s−1, favour the possibility of the absorption tracing circumgalactic gas. The absorber serves as an example of weak Mg  ii –O  vi systems as a means to study multiphase high-velocity clouds in external galaxies. [ABSTRACT FROM AUTHOR]

We probe the high-ionization circumgalactic medium by examining absorber kinematics, absorber–galaxy kinematics, and average absorption profiles of 31 O vi absorbers from the "Multiphase Galaxy Halos" Survey as a function of halo mass, redshift, inclination, and azimuthal angle. The galaxies are isolated at 0.12 < zgal < 0.66 and are probed by a background quasar within D ≈ 200 kpc. Each absorber–galaxy pair has Hubble Space Telescope images and COS quasar spectra, and most galaxy redshifts have been accurately measured from Keck/ESI spectra. Using the pixel-velocity two-point correlation function (TPCF) method, we find that O vi absorber kinematics have a strong halo mass dependence. Absorbers hosted by ∼L* galaxies have the largest velocity dispersions, which we interpret to be that the halo virial temperature closely matches the temperature at which the collisionally ionized O vi fraction peaks. Lower-mass galaxies and group environments have smaller velocity dispersions. Total column densities follow the same behavior, consistent with theoretical findings. After normalizing out the observed mass dependence, we studied absorber–galaxy kinematics with a modified TPCF and found nonvirialized motions due to outflowing gas. Edge-on minor-axis gas has large optical depths concentrated near the galaxy systemic velocity as expected for bipolar outflows, while face-on minor-axis gas has a smoothly decreasing optical depth distribution out to large normalized absorber–galaxy velocities, suggestive of decelerating outflowing gas. Accreting gas signatures are not observed owing to "kinematic blurring," in which multiple line-of-sight structures are observed. These results indicate that galaxy mass dominates O vi properties over baryon cycle processes. [ABSTRACT FROM AUTHOR]

We present an ultraviolet quasar absorption line analysis of metal lines associated with three strong intervening H  i absorbers (with |$N(\rm {{H}\,{\small I}})$| > 1016.5 cm−2) detected in the outskirts of Sunyaev–Zel'dovich (SZ) effect-selected galaxy clusters (z cl ∼ 0.4–0.5), within clustocentric impact parameters of ρcl ∼ (1.6–4.7) r 500. Discovered in a recent set of targeted far-UV HST /COS spectroscopic observations, these absorbers have among the highest H  i column densities ever observed in the outskirts of galaxy clusters, and are also rich in metal absorption lines. Photoionization models yield single phase solutions for the three absorbers with gas densities of n H  ∼ 10−3–10−4 cm−3 and metallicities of [X/H] > −1.0 (from one-tenth solar to near-solar). The widths of detected absorption lines suggest gas temperatures of T ∼ 104 K. The inferred densities (temperatures) are significantly higher (lower) compared to the X-ray emitting intracluster medium in cluster cores. The absorbers are tracing a cool phase of the intracluster gas in the cluster outskirts, either associated with gas stripped from cluster galaxies via outflows, tidal streams or ram-pressure forces, or denser regions within the intracluster medium that were uniformly chemically enriched from an earlier epoch of enhanced supernova and Active Galactic Nucleus (AGN) feedback. [ABSTRACT FROM AUTHOR]

We present analysis on three intervening H  i –C  iv absorption systems tracing gas within galaxy group/cluster environments, identified in the HST /COS far-UV spectra of the background quasars PG 1148 + 549 (⁠|$z$| abs = 0.003 46), SBS 1122 + 594 (⁠|$z$| abs = 0.004 02), and RXJ 1230.8 + 0115 (⁠|$z$| abs = 0.005 74). The ionization models are consistent with the origin of metal lines and H  i from a cool and diffuse photoionized gas phase with T ≲ 4 × 104 K and |$n_{{{\rm H}\,}} \lesssim 5 \times 10^{-4}$|  cm−3. The three absorbers have 89, 51, and 17 galaxies detected within 1 Mpc and |Δ |$v$| | < 600 km s−1. The RXJ 1230.8 + 0115 sightline traces the outskirt regions of the Virgo cluster where the absorber is found to have supersolar metallicity. The detection of metal lines along with H  i has enabled us to confirm the presence of cool, diffuse gas possibly enriched by outflows, and tidal interactions in environments with significant galaxy density. [ABSTRACT FROM AUTHOR]

Compact groups of galaxies provide conditions similar to those experienced by galaxies in the earlier universe. Recent work on compact groups has led to the discovery of a dearth of mid-infrared transition galaxies (MIRTGs) in Infrared Array Camera (3.6-8.0 μm) color space as well as at intermediate specific star formation rates. However, we find that in compact groups these MIRTGs have already transitioned to the optical ([g–r]) red sequence. We investigate the optical color-magnitude diagram (CMD) of 99 compact groups containing 348 galaxies and compare the optical CMD with mid-infrared (mid-IR) color space for compact group galaxies. Utilizing redshifts available from Sloan Digital Sky Survey, we identified new galaxy members for four groups. By combining optical and mid-IR data, we obtain information on both the dust and the stellar populations in compact group galaxies. We also compare with more isolated galaxies and galaxies in the Coma Cluster, which reveals that, similar to clusters, compact groups are dominated by optically red galaxies. While we find that compact group transition galaxies lie on the optical red sequence, LVL+SINGS mid-IR transition galaxies span the range of optical colors. The dearth of mid-IR transition galaxies in compact groups may be due to a lack of moderately star-forming low mass galaxies; the relative lack of these galaxies could be due to their relatively small gravitational potential wells. This makes them more susceptible to this dynamic environment, thus causing them to more easily lose gas or be accreted by larger members. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a study of the evolution of several classes of Mg ii absorbers, and their corresponding Fe ii absorption, over a large fraction of cosmic history: 2.3-8.7 Gyr from the big bang. Our sample consists of 87 strong ( [ABSTRACT FROM AUTHOR]

We present a spectroscopic survey of 21 young massive clusters and complexes and one tidal dwarf galaxy (TDG) candidate in Stephan's Quintet, an interacting compact group of galaxies. All of the selected targets lie outside the main galaxies of the system and are associated with tidal debris. We find clusters with ages between a few and 125 Myr and confirm the ages estimated through Hubble Space Telescope photometry by Fedotov et al., as well as their modeled interaction history of the Quintet. Many of the clusters are found to be relatively long-lived, given their spectrosopically derived ages, while their high masses suggest that they will likely evolve to eventually become intergalactic clusters. One cluster, T118, is particularly interesting, given its age (~125 Myr), high mass (~2 x 106 M☉), and position in the extreme outer end of the young tidal tail. This cluster appears to be quite extended (Reff ~ 12-15 pc) compared to clusters observed in galaxy disks (Reff ~ 3-4 pc), which confirms an effect we previously found in the tidal tails of NGC 3256, where clusters are similarly extended. We find that star and cluster formation can proceed at a continuous pace for at least ~150 Myr within the tidal debris of interacting galaxies. The spectrum of the TDG candidate is dominated by a young population (~7 Myr), and, assuming a single age for the entire region, has a mass of at least 106 M☉. [ABSTRACT FROM AUTHOR]

We use high-resolution Keck, VLT, or Hubble Space Telescope spectra of background quasars to examine the kinematic properties of the multiphase, metal-enriched circumgalactic medium in the outskirts of galaxies at 0.08 < zgal < 1.0, focusing on the low-ionization Mgii and high-ionization Ovi doublets. The absorption kinematics of low-ionization gas in the circumgalactic medium depend strongly on the star formation activity and the location about the host galaxy, where the largest velocity dispersions are associated with blue, face-on galaxies probed along the minor axis. Conversely, high-ionization gas kinematics are independent of galaxy star formation activity and orientation. [ABSTRACT FROM PUBLISHER]

We have discovered that warm gas flows along galaxy major and minor axes detected out to 200 kpc. Our results are derived from a sample of HST-imaged isolated galaxies with nearby background quasars used to probe their 105K CGM detected in HST/COS UV spectra (traced by Ovi absorption). We constrain the geometry of the gas to reside between 20-40 degrees of the projected major axis and within 60 degrees of the projected minor axis, with little-to-no gas found in between. Furthermore, strong absorption systems tend to be found along the minor axes of star-forming galaxies. All of our results are consistent with the current view of the CGM originating from major axis-fed inflows/recycled gas and from minor axis-driven outflows. [ABSTRACT FROM PUBLISHER]

Superstar clusters are young, compact star clusters found in the central regions of interacting galaxies. Recently, they have also been reported to preferentially form in certain tidal tails, but not in others. In this paper, we have used 21-cm H i maps and the Hubble Space Telescope Wide Field Planetary Camera 2 images of eight tidal tail regions of four merging galaxy pairs to compare the kiloparsec scale H i distribution with the location of superstar clusters found from the optical images. For most of the tails, we find that there is an increase in superstar cluster density with increasing projected H i column density, such that the star cluster density is highest when log , but equal to the background count rate at lower H i column density. However, for two tails (NGC 4038/39 Pos A and 3921), there is no significant star cluster population despite the presence of gas at high column density. This implies that the threshold is a necessary but not sufficient condition for cluster formation. Gas volume density is likely to provide a more direct criterion for cluster formation, and other factors such as gas pressure or strength of encounter may also have an influence. Comparison of H i thresholds needed for formation of different types of stellar structures await higher resolution H i and optical observations of larger numbers of interacting galaxies. [ABSTRACT FROM AUTHOR]

We have monitored 12 intrinsic narrow absorption lines (NALs) in five quasars and seven mini-broad absorption lines (mini-BALs) in six quasars for a period of 4-12 yr (1-3.5 yr in the quasar rest-frame). We present the observational data and the conclusions that follow immediately from them, as a prelude to a more detailed analysis. We found clear variability in the equivalent widths (EWs) of the mini-BAL systems but no easily discernible changes in their profiles. We did not detect any variability in the NAL systems or in narrow components that are often located at the center of mini-BAL profiles. Variations in mini-BAL EWs are larger at longer time intervals, reminiscent of the trend seen in variable BALs. If we assume that the observed variations result from changes in the ionization state of the mini-BAL gas, we infer lower limits to the gas density ∼103-105 cm–3 and upper limits on the distance of the absorbers from the central engine of the order of a few kiloparsecs. Motivated by the observed variability properties, we suggest that mini-BALs can vary because of fluctuations of the ionizing continuum or changes in partial coverage while NALs can vary primarily because of changes in partial coverage. [ABSTRACT FROM AUTHOR]

We present an analysis of the diffuse X-ray emission in 19 compact groups (CGs) of galaxies observed with Chandra. The hottest, most X-ray luminous CGs agree well with the galaxy cluster X-ray scaling relations in LX-T and LX-σ, even in CGs where the hot gas is associated with only the brightest galaxy. Using Spitzer photometry, we compute stellar masses and classify Hickson CGs 19, 22, 40, and 42, and RSCGs 32, 44, and 86 as fossil groups using a new definition for fossil systems that includes a broader range of masses. We find that CGs with total stellar and H I masses ≳ 1011.3M☼ are often X-ray luminous, while lower-mass CGs only sometimes exhibit faint, localized X-ray emission. Additionally, we compare the diffuse X-ray luminosity against both the total UV and 24 μm star formation rates of each CG and optical colors of the most massive galaxy in each of the CGs. The most X-ray luminous CGs have the lowest star formation rates, likely because there is no cold gas available for star formation, either because the majority of the baryons in these CGs are in stars or the X-ray halo, or due to gas stripping from the galaxies in CGs with hot halos. Finally, the optical colors that trace recent star formation histories of the most massive group galaxies do not correlate with the X-ray luminosities of the CGs, indicating that perhaps the current state of the X-ray halos is independent of the recent history of stellar mass assembly in the most massive galaxies. [ABSTRACT FROM AUTHOR]

Dynamic interactions between the two Magellanic Clouds have flung large quantities of gas into the halo of the Milky Way. The result is a spectacular arrangement of gaseous structures, including the Magellanic Stream, the Magellanic Bridge, and the Leading Arm (collectively referred to as the Magellanic System). In this third paper of a series studying the Magellanic gas in absorption, we analyze the gas ionization level using a sample of 69 Hubble Space Telescope/Cosmic Origins Spectrograph sightlines that pass through or within 30° of the 21 cm emitting regions. We find that 81% (56/69) of the sightlines show UV absorption at Magellanic velocities, indicating that the total cross-section of the Magellanic System is ≈11,000 deg2, or around one-quarter of the entire sky. Using observations of the Si III/Si II ratio together with Cloudy photoionization modeling, we calculate the total gas mass (atomic plus ionized) of the Magellanic System to be ≈2.0 × 109M☼ (d/55 kpc)2, with the ionized gas contributing around three times as much mass as the atomic gas. This is larger than the current-day interstellar H I mass of both Magellanic Clouds combined, indicating that they have lost most of their initial gas mass. If the gas in the Magellanic System survives to reach the Galactic disk over its inflow time of ∼0.5-1.0 Gyr, it will represent an average inflow rate of ∼3.7-6.7 M☼ yr–1, potentially raising the Galactic star formation rate. However, multiple signs of an evaporative interaction with the hot Galactic corona indicate that the Magellanic gas may not survive its journey to the disk fully intact and will instead add material to (and cool) the corona. [ABSTRACT FROM AUTHOR]