Search

We present an all-southern sky survey for MgII doublet absorbers in 951 z < 4 AGN/quasar spectra from the Australian Dark Energy Survey (OzDES). The spectral resolution ranges from R = 1400-1700 over the wavelengths 3700 A-8800 A. The survey has a 5sigma detection completeness of 50% and above for rest-frame equivalent widths W_r(2796) >= 0.3 A. We studied 656 MgII absorption systems over the redshift range 0.33 < z < 2.19 with equivalent widths 0.3 < W_r(2796) < 3.45 A. The equivalent width distribution is well fit by an exponential function with W* = 0.76 +/- 0.04 A and the redshift path density exhibits very little evolution. Overall, our findings are consistent with the large, predominantly northern-sky, surveys of MgII absorbers. We developed and implemented a Monte Carlo model informed by a high-resolution MgII survey for determining the MgII mass density, Omega_MgII. We found Omega_MgII ~ 5 x 10^-7 with no evidence of evolution over a ~7 Gyr time span following Cosmic Noon. Incorporating measurements covering 2.0 < z < 6.4 from the literature, we extended our insights into MgII mass density evolution from the end of reionization well past the Cosmic Noon epoch. The presented Monte Carlo model has potential for advancing our knowledge of the evolution of mass densities of metal-ions common to quasar absorption line studies, as it exploits the efficiency of large low-resolution surveys while requiring only small samples from expensive high-resolution surveys., Comment: 27 pages, 15 figures, 3 tables. Accepted on Pi Day 2024

The pervasive presence of warm gas in galaxy halos 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 analyzing 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 ($T \sim$ 10$^{4.1}$ K) in photoionization equilibrium, warm-hot collisionally ionized clouds ($T \sim$ 10$^{4.5-5}$ K) affected by time-dependent photoionization, and hotter clouds ($T \sim$ 10$^{5.4-6}$ K) with broad OVI and Lya 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., Comment: Accepted for publication in MNRAS

The 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 HI that is aligned with galaxy rotation with the equivalent width co-rotation fraction, $f_{\rm EWcorot}$. Using 70 quasar sightlines having HST/COS HI absorption (${12<\log (N(HI)/{\rm cm}^{-2})<20}$) within $5R_{\rm vir}$ of $z<0.6$ galaxies we find that $f_{\rm EWcorot}$ increases with increasing HI column density. $f_{\rm EWcorot}$ is flat at $\sim0.6$ within $R_{\rm vir}$ and decreases beyond $R_{\rm vir}$ to $f_{\rm EWcorot}$$\sim0.35$. $f_{\rm EWcorot}$ 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 two for edge-on galaxies. Inside $R_{\rm vir}$, co-rotation dominated HI is located within $\sim 20$ deg of the major and minor axes. We surprisingly find equal amounts of HI 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$_{\rm h}/M_{\odot})>12$ 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., Comment: 22 pages, 11 figures, accepted for publication in MNRAS July 26th 2024

The multiphase 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 HST/COS (including, but not limited to, SiII, CII, SiIII, CIII, and OVI) within $21\leq D\leq~276$ 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(HI). The $f_{\rm EWcorot}$ of lower ionization gas decreases with increasing $D/R_{\rm vir}$ while OVI and HI 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 OVI detections enabled us to investigate where the majority of co-rotating gas is found. Highly co-rotating OVI primarily resides along the galaxies' major axis. Looking at the $f_{\rm EWcorot}$ as a function of ionization potential (${d{f_{\rm EWcorot}}}/{d{(eV)}}$), 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., Comment: 18 pages, 11 figures, accepted for publication in MNRAS 2024 September 9

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 2022

A key assumption in quasar absorption line studies of the circumgalactic medium (CGM) is that each absorption component maps to a spatially isolated "cloud" structure that has single valued properties (e.g. density, temperature, metallicity). We aim to assess and quantify the degree of accuracy underlying this assumption. We used adaptive mesh refinement hydrodynamic cosmological simulations of two $z=1$ dwarf galaxies and generated synthetic quasar absorption-line spectra of their CGM. For the SiII $\lambda 1260$ transition, and the CIV $\lambda\lambda1548, 1550$ and OVI $\lambda\lambda1031, 1037$ fine-structure doublets, we objectively determined which gas cells along a line-of-sight (LOS) contribute to detected absorption. We implemented a fast, efficient, and objective method to define individual absorption components in each absorption profile. For each absorption component, we quantified the spatial distribution of the absorbing gas. We studied a total of 1,302 absorption systems containing a total of 7,755 absorption components. 48% of SiII, 68% of CIV, and 72% of OVI absorption components arise from two or more spatially isolated "cloud" structures along the LOS. Spatially isolated "cloud" structures were most likely to have cloud-cloud LOS separations of 0.03$R_{vir}$, 0.11$R_{vir}$, and 0.13$R_{vir}$ for SiII, CIV, and OVI, respectively. There can be very little overlap between multi-phase gas structures giving rise to absorption components. If our results reflect the underlying reality of how absorption lines record CGM gas, they place tension on current observational analysis methods as they suggest that component-by-component absorption line formation is more complex than is assumed and applied for chemical-ionisation modelling., Comment: Submitted for publication in MNRAS on 02/24/2022

We use the observed cumulative statistics of CIV absorbers and dark matter halos to infer the distribution of CIV-absorbing gas relative to galaxies at redshifts $0\!\leq\!z\!\leq\!5$. We compare the cosmic incidence $dN/dX$ of CIV absorber populations and galaxy halos, finding that massive $L \geq L_{\star}$ halos alone cannot account for all the observed $W_r \geq 0.05$~{\AA} absorbers. However, the $dN/dX$ of lower mass halos exceeds that of $W_r \geq 0.05$~{\AA} absorbers. We also estimate the characteristic gas radius of absorbing structures required for the observed CIV $dN/dX$, assuming each absorber is associated with a single galaxy halo. The $W_r \geq 0.3$~{\AA} and $W_r \geq 0.6$~{\AA} CIV gas radii are $\sim30-70\%$ ($\sim20-40\%$) of the virial radius of $L_{\star}$ ($0.1L_{\star}$) galaxies, and the $W_r \geq 0.05$~{\AA} gas radius is $\sim100-150\%$($\sim60-100\%$) of the virial radius of $L_{\star}$ ($0.1L_{\star}$) galaxies. For stronger absorbers, the gas radius relative to virial radius rises across Cosmic Noon and falls afterwards, while for weaker absorbers, the relative gas radius declines across Cosmic Noon and then dramatically rises at $z\!<\!1$. A strong luminosity-dependence of gas radius implies highly extended CIV envelopes around massive galaxies before Cosmic Noon, while a luminosity-independent gas radius implies highly extended envelopes around dwarf galaxies after Cosmic Noon. From available absorber-galaxy and CIV evolution data, we favor a scenario in which low-mass galaxies enrich the volume around massive galaxies at early epochs and propose that the outer halo gas ($>0.5R_v$) was produced primarily in ancient satellite dwarf galaxy outflows, while the inner halo gas ($<0.5R_v$) originated from the central galaxy and persists as recycled accreting gas., Comment: Accepted to ApJ; 22 pages (17 pages main text); 7 figures

We used adaptive mesh refinement hydrodynamic cosmological simulations of a $z=1$ Milky Way-type galaxy and a $z=0$ Dwarf galaxy and generated synthetic quasar absorption-line spectra of their circumgalactic medium (CGM). Our goal is to assess whether standard observational spectroscopic analysis methods accurately reproduce intrinsic column densities, metallicities [Si/H], and hydrogen densities $n_{H}$, in simulated absorption-line systems. Without knowledge of the intrinsic simulated properties (blind study), we analysed synthetic COS and HIRES spectra with fixed $S/N=30$ to determine the column densities, metallicity, and $n_{H}$, using Voigt profile fitting combined with Markov-Chain Monte-Carlo single-phase {\sc Cloudy} modelling techniques. To quantify the intrinsic simulated absorbing gas properties, we objectively determined which gas cells along a line of sight (LOS) contribute to detected absorption in the spectra and adopt the unweighted geometric mean of these gas cell properties. For this pilot study, we performed this experiment for five LOS in the Milky-Way galaxy and five LOS in the Dwarf galaxy. We found an average agreement between the "observed" and intrinsic metallicity overestimated within $0.8\sigma$ or $0.2$ dex for the "Milky-Way"' CGM and overestimated within $1.4\sigma$ or $0.2$ dex for the Dwarf galaxy CGM. We found that the spectroscopically-derived $n_{H}$ are underestimated within $0.8\sigma$ or $0.4$ dex of the intrinsic $n_{H}$ for the "Milky-Way" CGM and overestimated within $0.3\sigma$ or $0.3$ dex for the Dwarf galaxy CGM. The overall agreement suggests that, for single-phase ionisation modelling of systems where there is substantial spread in gas properties, global metallicity measurements from quasar absorption line studies are capturing the average metallicity and ionisation parameters in a given astrophysical environment., Comment: Submitted to MNRAS on August 6th, 2021. Accepted for publication on October 4th, 2021

We have obtained new observations of the absorption system at $z_\mathrm{abs}=0.48$ toward QSO Q0454-220, which we use to constrain its chemical and physical conditions. The system features metal-enriched gas and previously unknown low-metallicity gas detected $\sim 200 \, \mathrm{km \, s^{-1}}$ blueward of the metal-enriched gas. The low-metallicity gas is detected in multiple Lyman series lines but is not detected in any metal lines. Our analysis includes low-ionization (e.g., Fe II, Mg II) metal lines, high-ionization (e.g., C IV, O VI, N V) metal lines, and several Lyman series lines. We use new UV spectra taken with HST/COS along with data taken from HST/STIS, Keck/HIRES, and VLT/UVES. We find that the absorption system can be explained with a photoionized low-ionization phase with $\mathrm{[Fe/H]} \sim -0.5$ and $n_\mathrm{H} \sim 10^{-2.3} \, \mathrm{cm}^{-3}$, a photoionized high-ionization phase with a conservative lower limit of $-3.3 < \mathrm{[Fe/H]}$ and $n_\mathrm{H} \sim 10^{-3.8} \, \mathrm{cm}^{-3}$, and a low-metallicity component with a conservative upper limit of $\mathrm{[Fe/H]} < -2.5$ that may be photoionized or collisionally ionized. We suggest that the low-ionization phase may be due to cold-flow accretion via large-scale filamentary structure or due to recycled accretion while the high-ionization phase is the result of ancient outflowing material from a nearby galaxy. The low-metallicity component may come from pristine accretion. The velocity spread and disparate conditions among the absorption system's components suggest a combination of gas arising near galaxies along with gas arising from intergroup material., Comment: 18 pages, 9 figures; updated author affiliation

We use adaptive mesh refinement cosmological simulations to study the spatial distribution and covering fraction of OVI 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 sightlines having a distribution of $D/R_{vir}$ and sightline orientation statistically consistent with the observations. We find that the OVI covering fraction obtained for the simulated galaxies agrees well with the observed value for the inner halo ($D/R_{vir} \leq 0.375$) and is within $1.1\sigma$ in the outer halo ($D/R_{vir} > 0.75$), but is underproduced within $0.375 < D/R_{vir} \leq 0.75$. The observed bimodal distribution of OVI covering fraction with azimuthal angle, showing 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 OVI absorbing gas is dominated by outflows in the inner halo mixed with a inflowing gas that originates from further out in the halo. Though the CGM of the individual simulated galaxies exhibit 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., Comment: Accepted on December 1, 2020 for publication in The Astrophysical Journal

The multi-phase circumgalactic medium (CGM) arises within the complex environment around a galaxy, or collection of galaxies, and possibly originates from a wide range of physical mechanisms. In this paper, we attempt to disentangle the origins of these multi-phase structures and present a detailed analysis of the quasar field Q0122-003 field using Keck/KCWI galaxy observations and HST/COS spectra probing the CGM. Our re-analysis of this field shows that there are two galaxies associated with the absorption. We have discovered a dwarf galaxy, G_27kpc ($M_{\star}=10^{8.7}$ M$_{\odot}$), at z=0.39863 that is 27 kpc from the quasar sightline. G_27kpc is only +21 km/s from a more massive ($M_{\star}=10^{10.5}$ M$_{\odot}$) star-forming galaxy, G_163kpc, at an impact parameter of 163 kpc. While G_163kpc is actively forming stars (SFR=6.9 M$_{\odot}$ yr$^{-1}$), G_27kpc has a low star-formation rate (SFR=$0.08\pm0.03$ M$_{\odot}$ yr$^{-1}$) and star formation surface density ($\Sigma_{SFR}=0.006$ M$_{\odot}$ kpc$^{-2}$ yr$^{-1}$), implying no active outflows. By comparing galaxy SFRs, kinematics, masses and distances from the quasar sightline to the absorption kinematics, column densities and metallicities, we have inferred the following: (1) Part of the low-ionization phase has a metallicity and kinematics consistent with being accreted onto G_27kpc. (2) The remainder of the low ionization phase has metallicities and kinematics consistent with being intragroup gas being transferred from G_27kpc to G_163kpc. (3) The high ionization phase is consistent with being produced solely by outflows originating from the massive halo of G_163kpc. Our results demonstrate the complex nature of the multi-phase CGM, especially around galaxy groups, and that detailed case-by-case studies are critical for disentangling its origins., Comment: 13 pages, 4 figures, accepted for publication in MNRAS 2020 November 10

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 degrees) disk galaxy (G1547) where the CGM is probed by a background quasar at a distance of 84 kpc and within 10 degrees of the galaxy major axis. G1547 does not have any detectable CGM absorption down to stringent limits, covering HI (EW$_r$<0.02A, log(N(HI)/cm$^{-2}$)<12.6) and a range of low and high ionisation absorption lines (OI, CII, NII, SiII, CIII, NIII, SiIII, CIV, SiIV, NV and OVI). 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 SFR (1.1 M$_{\odot}$yr$^{-1}$), SSFR ($1.5\times10^{-10}$yr$^{-1}$) and $\Sigma_{\rm SFR}$ (0.06 M$_{\odot}$yr$^{-1}$kpc$^{-2}$) and does not exhibit AGN 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 HI absorption-selected galaxies, we find that quiescent galaxies with log(SSFR/yr$^{-1})<-11$ have a low probability (4/12) of possessing detectable HI in their CGM, while all galaxies (40/40) with log(SSFR/yr$^{-1})>-11$ have HI absorption. We conclude that SSFR is a good indicator of the presence of HI 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 timescale of $4\pm1$ Gyr. G1547 provides a unique perspective into the external mechanisms that could explain the migration of galaxies into the green valley., Comment: 14 pages, 9 figures, 2 tables. Accepted to MNRAS on November 4, 2020

We present the Voigt profile (VP) models, column densities, Doppler b parameters, kinematics, and distribution of components for 422 MgII absorbers found in a survey of 249 HIRES and UVES quasar spectra. The equivalent width range of the sample is 0.006 < W_r(2796) < 6.23 angstroms (A) and the redshift range is 0.19 < z < 2.55, with a mean of = 1.18. Based on historical precedent, we classified 180 absorbers as weak systems (W_r(2796) < 0.3 A) and 242 as strong systems (W_r(2796) >= 0.3 A). Assuming a minimum number of significant components per system, the VP fitting, yielded a total of 2,989 components, with an average of 2.7 and 10.3 components found for the weak and strong MgII subsamples, respectively. The VP component line density for the full sample is 8.62 +/- 0.23 clouds/A. The distribution of VP component column density over the range 12.4 < log[N(MgII)] < 17.0 [ions cm^-2] is well modeled with a power-law slope of -1.45 +/- 0.01. The median Doppler b parameters are 4.5 +/- 3.5 km/s, 6.0 +/- 4.5 km/s and 5.7 +/- 4.4 km/s for the weak, strong, and full samples. We modeled the probability of component velocity splitting (the two-point velocity correlation function, TPCF) of our full sample using a three-component composite Gaussian function. Our resulting velocity dispersions are 25.4, 68.7, and 207.1 km/s, respectively. These data provide an excellent database for studying the cosmic evolution of MgII absorber kinematic evolution., Comment: 22 pages, 9 figures, accepted to ApJ

We present a large high-resolution study of the distribution and evolution of CIV absorbers, including the weakest population with equivalent widths $W_r<0.3$~{\AA}. By searching 369 high-resolution, high signal-to-noise spectra of quasars at $1.1\leq z_{em} \leq5.3$ from Keck/HIRES and VLT/UVES, we find $1268$ CIV absorbers with $W_r \geq 0.05$~{\AA} (our $\sim50\%$ completeness limit) at redshifts $1\leq z \leq4.75$. A Schechter function describes the observed equivalent width distribution with a transition from power-law to exponential decline at $W_r \gtrsim 0.5$~{\AA}. The power-law slope $\alpha$ rises by $\sim7\%$ and transition equivalent width $W_{\star}$ falls by $\sim\!20\%$ from $\langle z \rangle=1.7$ to $\langle z \rangle=3.6$. We find that the co-moving redshift path density, $dN/dX$, of $W_r \geq 0.05$~{\AA} absorbers rises by $\sim1.8$ times from $z\simeq 4.0$ to $z\simeq 1.3$, while the $W_r \geq 0.6$~{\AA} $dN/dX$ rises by a factor of $\sim8.5$. We quantify the observed evolution by a model in which $dN/dX$ decreases linearly with redshift. The model suggests that populations with larger $W_r$ thresholds evolve faster with redshift and appear later in the universe. The cosmological Technicolor Dawn simulations at $z=3-5$ over-produce the observed abundance of absorbers with $W_r<0.3$~{\AA}, while yielding better agreement at higher $W_r$. Our empirical linear model successfully describes {CIV evolution in the simulations and the observed evolution of $W_r \geq 0.6$~{\AA} CIV for the past $\sim12$ Gyr. Combining our measurements with the literature gives us a picture of CIV-absorbing structures becoming more numerous and/or larger in physical size over the last $\approx13$ Gyr of cosmic time ($z\sim6$ to $z\sim0$)., Comment: 27 pages, 13 figures, 7 tables; submitted to ApJ on July 22, 2020; revised September 28, 2020; accepted October 2, 2020

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 table

We present the first results from our CGM at Cosmic Noon with KCWI program to study gas flows in the circumgalactic medium (CGM) at $z=2-3$. Combining the power of a high-resolution VLT/UVES quasar spectrum, an HST/ACS image, and integral field spectroscopy with Keck/KCWI, we detected Lya emission from a $1.7L_{\ast}$ galaxy at $z_{\rm gal}=2.0711$ associated with a Lyman limit system with weak MgII ($W_r(2796)=0.24$ Ang) in quasar field J143040$+$014939. The galaxy is star-forming (${\rm SFR}_{\rm FUV}=37.8$ M$_{\odot}$ yr$^{-1}$) and clumpy: either an edge-on disk ($i=85^{\circ}$) or, less likely, a major merger. The background quasar probes the galaxy at an impact parameter of $D=66$ kpc along the projected galaxy minor axis ($\Phi=89^{\circ}$). From photoionization modeling of the absorption system, we infer a total line-of-sight CGM metallicity of ${\rm [Si/H]}=-1.5^{+0.4}_{-0.3}$. The absorption system is roughly kinematically symmetric about $z_{\rm gal}$, with a full MgII velocity spread of $\sim210$ km s$^{-1}$. Given the galaxy-quasar orientation, CGM metallicity, and gas kinematics, we interpret this gas as an outflow that has likely swept-up additional material. By modeling the absorption as a polar outflow cone, we find the gas is decelerating with average radial velocity $V_{\rm out}=109-588$ km s$^{-1}$ for half opening angles of $\theta_0=14^{\circ}-75^{\circ}$. Assuming a constant $V_{\rm out}$, it would take on average $t_{\rm out}\sim111-597$ Myr for the gas to reach 66 kpc. The outflow is energetic, with a mass outflow rate of $\dot{M}_{\rm out}<52{\pm37}$ M$_{\odot}$ yr$^{-1}$ and mass loading factor of $\eta<1.4{\pm1.0}$. We aim to build a sample of $\sim50$ MgII absorber--galaxy pairs at this epoch to better understand gas flows when they are most actively building galaxies., Comment: 30 pages, 9 figures, 5 tables. Accepted for publication in ApJ on 26 October 2020

We examine the properties of damped Lyman-$\alpha$ absorbers (DLAs) emerging from a single set of cosmological initial conditions in two state-of-the-art cosmological hydrodynamic simulations: {\sc Simba} and {\sc Technicolor Dawn}. The former includes star formation and black hole feedback treatments that yield a good match with low-redshift galaxy properties, while the latter uses multi-frequency radiative transfer to model an inhomogeneous ultraviolet background (UVB) self-consistently and is calibrated to match the Thomson scattering optical depth, UVB amplitude, and Ly-$\alpha$ forest mean transmission at $z>5$. Both simulations are in reasonable agreement with the measured stellar mass and star formation rate functions at $z\geq 3$, and both reproduce the observed neutral hydrogen cosmological mass density, $\Omega_{\rm HI}(z)$. However, the DLA abundance and metallicity distribution are sensitive to the galactic outflows' feedback and the UVB amplitude. Adopting a strong UVB and/or slow outflows under-produces the observed DLA abundance, but yields broad agreement with the observed DLA metallicity distribution. By contrast, faster outflows eject metals to larger distances, yielding more metal-rich DLAs whose observational selection may be more sensitive to dust bias. The DLA metallicity distribution in models adopting an ${\rm H}_2$-regulated star formation recipe includes a tail extending to $[M/H] \ll -3$, lower than any DLA observed to date, owing to curtailed star formation in low-metallicity galaxies. Our results show that DLA observations play an imporant role in constraining key physical ingredients in galaxy formation models, complementing traditional ensemble statistics such as the stellar mass and star formation rate functions., Comment: Accepted for publication in MNRAS

We present ISM and CGM metallicities for 25 absorption systems associated with isolated star-forming galaxies (=0.28) with 9.417.2) reside along the minor axis. This suggest N(HI) could be a useful indicator of accretion/outflows. We conclude that CGM is not well mixed, given the range of galaxy-CGM metallicities, and that metallicity at low redshift might not be a good tracer of CGM processes. Furthermore we should replace integrated line-of-sight, single phase, metallicities with multi-phase, cloud-cloud metallicities, which could be more indicative of the physical processes within the CGM., Comment: 10 pages, 6 figures, 1 table. Accepted to ApJ on October 7, 2019

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 2019

We probe the high-ionization circumgalactic medium by examining absorber kinematics, absorber-galaxy kinematics, and average absorption profiles of 31 OVI 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

We present observations of 50 pairs of redshift z ~ 0.2 star-forming galaxies and background quasars. These sightlines probe the circumgalactic medium (CGM) out to half the virial radius, and we describe the circumgalactic gas kinematics relative to the reference frame defined by the galactic disks. We detect halo gas in MgII absorption, measure the equivalent-width-weighted Doppler shifts relative to each galaxy, and find that the CGM has a component of angular momentum that is aligned with the galactic disk. No net counter-rotation of the CGM is detected within 45 degrees of the major axis at any impact parameter. The velocity offset of the circumgalactic gas correlates with the projected rotation speed in the disk plane out to disk radii of roughly 70 kpc. We confirm previous claims that the MgII absorption becomes stronger near the galactic minor axis and show that the equivalent width correlates with the velocity range of the absorption. We cannot directly measure the location of any absorber along the sightline, but we explore the hypothesis that individual velocity components can be associated with gas orbiting in the disk plane or flowing radially outward in a conical outflow. We conclude that centrifugal forces partially support the low-ionization gas and galactic outflows kinematically disturb the CGM producing excess absorption. Our results firmly rule out schema for the inner CGM that lack rotation and suggest that angular momentum as well as galactic winds should be included in any viable model for the low-redshift CGM., Comment: Accepted for publication in the Astrophysical Journal

We present the first galaxy-OVI absorption kinematic study for 20 absorption systems (EW>0.1~{\AA}) associated with isolated galaxies (0.15$33^{\circ}$). OVI absorption along the galaxy major axis is not correlated with galaxy rotation kinematics, with only 1/10 systems that could be explained with rotation/accretion models. This is in contrast to co-rotation commonly observed for MgII absorption. OVI along the minor axis could be modeled by accelerating outflows but only for small opening angles, while the majority of the OVI is decelerating. Along both axes, stacked OVI profiles reside at the galaxy systemic velocity with the absorption kinematics spanning the entire dynamical range of their galaxies. The OVI found in AMR cosmological simulations exists within filaments and in halos of ~50 kpc surrounding galaxies. Simulations show that major axis OVI gas inflows along filaments and decelerates as it approaches the galaxy while increasing in its level of co-rotation. Minor axis outflows in the simulations are effective within 50-75 kpc beyond that they decelerate and fall back onto the galaxy. Although the simulations show clear OVI kinematic signatures they are not directly comparable to observations. When we compare kinematic signatures integrated through the entire simulated galaxy halo we find that these signatures are washed out due to full velocity distribution of OVI throughout the halo. We conclude that OVI alone does not serve as a useful kinematic indicator of gas accretion, outflows or star-formation and likely best probes the halo virial temperature., Comment: 24 pages, 21 figures, 4 tables. Accepted to ApJ on November 14, 2018

By comparing MgII absorption in the circumgalactic medium (CGM) of group environments to isolated galaxies, we investigated the impact of environment on the CGM. A MgII absorber is associated with a group if there are two or more galaxies at the absorption redshift within a projected distance of D=200 kpc from a background quasar and a line-of-sight velocity separation of 500 km/s. We compiled a sample of 29 group environments consisting of 74 galaxies (2-5 galaxies per group) at $0.113

We have obtained new observations of the partial Lyman limit absorber at \zabs$=0.93$ towards quasar PG~1206+459, and revisit its chemical and physical conditions. The absorber, with $ N(HI) \sim 10^{17.0}$ ~\sqcm\ and absorption lines spread over $\gtrsim$1000~\kms\ in velocity, is one of the strongest known OVI absorbers at $\log N(OVI)=$15.54$\pm$0.17. Our analysis makes use of the previously known low-(e.g. \MgII), intermediate-(e.g. SiIV), and high-ionization (e.g., CIV, NV, NeVIII) metal lines along with new $HST/$COS observations that cover OVI, and an $HST/$ACS image of the quasar field. Consistent with previous studies, we find that the absorber has a multiphase structure. The low-ionization phase arises from gas with a density of $\log (n_{\rm H}/\rm cm^{-3})\sim-2.5$ and a solar to super-solar metallicity. The high-ionization phase stems from gas with a significantly lower density, i.e. $\log (n_{\rm H}/\rm cm^{-3}) \sim-3.8$, and a near-solar to solar metallicity. The high-ionization phase accounts for all of the absorption seen in CIV, NV, and OVI. We find the the detected \NeVIII, reported by \cite{Tripp2011}, is best explained as originating in a stand-alone collisionally ionized phase at $T\sim10^{5.85}~\rm K$, except in one component in which both OVI and NeVIII can be produced via photoionization. We demonstrate that such strong OVI absorption can easily arise from photoionization at $z\gtrsim1$, but that, due to the decreasing extragalactic UV background radiation, only collisional ionization can produce large OVI features at $z\sim0$. The azimuthal angle of $\sim88$\degree\ of the disk of the nearest ($\rm 68~kpc$) luminous ($1.3L_*$) galaxy at $z_{\rm gal}=0.9289$, which shows signatures of recent merger, suggests that the bulk of the absorption arises from metal enriched outflows., Comment: 21 pages, 12 figures, accepted for publication in MNRAS

We present a study comparing OVI $\lambda\lambda$1031, 1037 doublet absorption found towards group galaxy environments with that of isolated galaxies. The OVI absorption in the circumgalactic medium (CGM) of isolated galaxies has been studied previously by the "Multiphase Galaxy Halos" survey, where the kinematics and absorption properties of the CGM have been investigated. We extend these studies to group environments. We define a galaxy group to have two or more galaxies having a line-of-sight velocity difference of no more than 1000 km/s and located within 350 kpc (projected) of a background quasar sightline. We identified a total of six galaxy groups associated with OVI absorption $W_{\rm r}>0.06$ {\AA} that have a median redshift of $\langle z_{\rm gal} \rangle = 0.1669$ and a median impact parameter of $\langle D \rangle = 134.1$ kpc. An additional 12 non-absorbing groups were identified with a median redshift of $\langle z_{\rm gal} \rangle = 0.2690$ and a median impact parameter of $\langle D \rangle = 274.0$ kpc. We find the average equivalent width to be smaller for group galaxies than for isolated galaxies $(3\sigma)$. However, the covering fractions are consistent with both samples. We used the pixel-velocity two-point correlation function method and find that the velocity spread of OVI in the CGM of group galaxies is significantly narrower than that of isolated galaxies $(10\sigma)$. We suggest that the warm/hot CGM does not exist as a superposition of halos, instead, the virial temperature of the halo is hot enough for OVI to be further ionised. The remaining OVI likely exists at the interface between hot, diffuse gas and cooler regions of the CGM., Comment: 10 pages, 5 figures, 3 tables. Accepted to ApJ on June 2nd, 2017

We present detailed measurements of the redshift path density, equivalent width distribution, column density distribution, and redshift evolution of ${\MgII}$ absorbers as measured in archival spectra from the UVES spectrograph at the Very Large Telescope (VLT/UVES) and the HIRES spectrograph at the Keck Telescope (Keck/HIRES) to equivalent width detection limits below $0.01$~{\AA}. This survey examines 432 VLT/UVES spectra from the UVES SQUAD collaboration and 170 Keck/HIRES spectra from the KODIAQ group, allowing for detections of intervening ${\MgII}$ absorbers spanning redshifts $0.1 < z < 2.6$. We employ an accurate, automated approach to line detection which consistently detects redshifted absorption lines. We measure the equivalent widths, apparent optical depth column densities, and velocity widths for each absorbing system. Using our complete sample of all detectable ${\MgII}$ absorbers, we can accurately determine the redshift path density of absorbers across cosmic time. We measure evolution in the comoving ${\MgII}$ line density, $dN\,/dX$, finding more high equivalent width absorbers at $z = 2$ than at present. We also measure evolution in the equivalent width distribution, parameterized by a Schechter function fit, finding a shallower weak-end slope for absorbers at redshifts between $1.53 < z < 2.64$ as compared to lower redshifts. Finally, we calculate the cosmic mass fraction of ${\MgII}$ using the column density distribution. We find that weak ${\MgII}$ absorbers, those with equivalent widths less than $0.3$~{\AA}, are physically distinct and evolve separately from very strong ${\MgII}$ absorbers, which have equivalent widths greater than $1.0$~{\AA}., Comment: 15 pages, 10 figures

The circumgalactic medium (CGM) traced by OVI $\lambda\lambda 1031, 1037$ doublet absorption has been found to concentrate along the projected major and minor axes of the host galaxies. This suggests that OVI traces accreting and outflowing gas, respectively, which are key components of the baryon cycle of galaxies. We investigate this further by examining the kinematics of 29 OVI absorbers associated with galaxies at $0.13 < z_{\rm gal} < 0.66$ as a function of galaxy color, inclination, and azimuthal angle. Each galaxy was imaged with HST and the absorption was detected in COS/HST spectra of nearby ($D<200$ kpc) background quasars. We use the pixel-velocity two-point correlation function to characterize the velocity spread of the absorbers, which is a method used previously for a sample of MgII absorber--galaxy pairs. The absorption velocity spread for OVI is more extended than MgII, which suggests that the two ions trace differing components of the CGM. Also contrary to MgII, the OVI absorption velocity spreads are similar regardless of galaxy color, inclination, and azimuthal angle. This indicates that the kinematics of the high ionization gas is not strongly influenced by the present star formation activity in the galaxy. The kinematic homogeneity of OVI absorption and its tendency to be observed mainly along the projected galaxy major and minor axes is likely due to varying ionization conditions and gas densities about the galaxy. Gas in intermediate azimuthal angles may be ionized out of the OVI phase, possibly resulting in an azimuthal angle dependence on the distribution of gas in higher ionization states., Comment: 12 pages, 6 figures, 2 tables. Accepted for publication in The Astrophysical Journal on November 22nd, 2016

We describe the kinematics of circumgalactic gas near the galactic plane, combining new measurements of galaxy rotation curves and spectroscopy of background quasars. The sightlines pass within 19--93 kpc of the target galaxy and generally detect Mg II absorption. The Mg II Doppler shifts have the same sign as the galactic rotation, so the cold gas co-rotates with the galaxy. Because the absorption spans a broader velocity range than disk rotation can explain, we explore simple models for the circumgalactic kinematics. Gas spiraling inwards (near the disk plane) offers a successful description of the observations. An Appendix describes the addition of tangential and radial gas flows and illustrates how the sign of the disk inclination produces testable differences in the projected line-of-sight velocity range. This inflow interpretation implies that cold flow disks remain common down to redshift $z \approx 0.2$ and prolong star formation by supplying gas to the disk., Comment: 25 pages, 11 figures. ApJ, in Press

Lyman- and Werner-band absorption of molecular hydrogen (H$_2$) is detected in $\sim$50% of low redshift ($z<1$) DLAs/sub-DLAs with $N$(H$_2$) > 10$^{14.4}$ cm$^{-2}$. However the true origin(s) of the H$_2$ bearing gas remain elusive. Here we report a new detection of an H$_{2}$ absorber at $z=$ 0.4298 in the HST/COS spectra of quasar PKS 2128-123. The total $N$(HI) of 10$^{19.50\pm0.15}$ cm$^{-2}$ classifies the absorber as a sub-DLA. H$_{2}$ absorption is detected up to the $J=3$ rotational level with a total $\log N$(H$_{2}$) = 16.36$\pm$0.08 corresponding to a molecular fraction of log $f$(H$_{2}$) = $-$2.84$\pm$0.17. The excitation temperature of $T_{ex}$ = 206$\pm$6K indicates the presence of cold gas. Using detailed ionization modelling we obtain a near-solar metallicity (i.e., [O/H]= $-$0.26$\pm$0.19) and a dust-to-gas ratio of $\log \kappa \sim -0.45$ for the H$_{2}$ absorbing gas. The host-galaxy of the sub-DLA is detected at an impact parameter of $\rho \sim$ 48 kpc with an inclination angle of $i \sim$ 48 degree and an azimuthal angle of $\Phi \sim$ 15 degree with respect to the QSO sightline. We show that co-rotating gas in an extended disk cannot explain the observed kinematics of Mg II absorption. Moreover, the inferred high metallicity is not consistent with the scenario of gas accretion. An outflow from the central region of the host-galaxy, on the other hand, would require a large opening angle (i.e., 2$\theta>$150 degree), much larger than the observed outflow opening angles in Seyfert galaxies, in order to intercept the QSO sightline. We thus favor a scenario in which the H$_2$ bearing gas is stemming from a dwarf-satellite galaxy, presumably via tidal and/or ram-pressure stripping. Detection of a dwarf galaxy candidate in the HST/WFPC2 image at an impact parameter of $\sim$12 kpc reinforces such an idea., Comment: Published in ApJ; arXiv version matches the published one ( http://dx.doi.org/10.3847/0004-637X/823/1/66 )

The equivalent widths of MgII absorption in the circumgalactic medium (CGM) trace the global star formation rate up to $z<6$, are larger for star-forming galaxies than passively-evolving galaxies, and decrease with increasing distance from the galaxy. We delve further into the physics involved by investigating gas kinematics and cloud column density distributions as a function of galaxy color, redshift, and projected distance from the galaxy (normalized by galaxy virial radius, $D/R_{\rm vir}$). For 39 isolated galaxies at $0.3

We report a bimodality in the azimuthal angle ($\Phi$) distribution of gas around galaxies traced by OVI absorption. We present the mean $\Phi$ probability distribution function of 29 HST-imaged OVI absorbing (EW>0.1A) and 24~non-absorbing (EW<0.1A) isolated galaxies (0.08

We present a detailed analysis of a large-scale galactic outflow in the CGM of a massive (M_h ~ 10^12.5 Msun), star-forming (6.9 Msun/yr), sub-L* (0.5 L_B*) galaxy at z=0.39853 that exhibits a wealth of metal-line absorption in the spectra of the background quasar Q 0122-003 at an impact parameter of 163 kpc. The galaxy inclination angle (i=63 degree) and the azimuthal angle (Phi=73 degree) imply that the QSO sightline is passing through the projected minor-axis of the galaxy. The absorption system shows a multiphase, multicomponent structure with ultra-strong, wide velocity spread OVI (logN = 15.16\pm0.04, V_{90} = 419 km/s) and NV (logN = 14.69\pm0.07, V_{90} = 285 km/s) lines that are extremely rare in the literature. The highly ionized absorption components are well explained as arising in a low density (10^{-4.2} cm^{-3}), diffuse (10 kpc), cool (10^4 K) photoionized gas with a super-solar metallicity ([X/H] > 0.3). From the observed narrowness of the Lyb profile, the non-detection of SIV absorption, and the presence of strong CIV absorption we rule out equilibrium/non-equilibrium collisional ionization models. The low-ionization photoionized gas with a density of 10^{-2.5} cm^{-3} and a metallicity of [X/H] > -1.4 is possibly tracing recycled halo gas. We estimate an outflow mass of ~2x10^{10} Msun, a mass-flow rate of ~54 Msun/yr, a kinetic luminosity of ~9x10^{41} erg/s, and a mass loading factor of ~8 for the outflowing high-ionization gas. These are consistent with the properties of "down-the-barrel" outflows from infrared-luminous starbursts as studied by Rupke et al. Such powerful, large-scale, metal-rich outflows are the primary means of sufficient mechanical and chemical feedback as invoked in theoretical models of galaxy formation and evolution., Comment: APJ accepted; Updated Fig. 2 with more galaxy info

We investigate the dependence of gas kinematics and column densities in the MgII-absorbing circumgalactic medium on galaxy color, azimuthal angle, and inclination to trace baryon cycle processes. Our sample of 30 foreground isolated galaxies at $0.3

We performed a detailed study of the extended cool gas, traced by MgII absorption [$W_r(2796)\geq0.3$~{\AA}], surrounding 14 narrow-line active galactic nuclei (AGNs) at 0.1250$ km/s, indicating outflowing gas. The 2/2 intrinsic MgII systems have outflow velocities a factor of $\sim4$ higher than the NaID outflow velocities. Our results are consistent with AGN-driven outflows destroying the cool gas within their halos, which dramatically decreases their cool gas covering fraction, while star-burst driven winds are expelling cool gas into their circumgalactic media (CGM). This picture appears contrary to quasar--quasar pair studies which show that the quasar CGM contains significant amounts of cool gas whereas intrinsic gas found `down-the-barrel' of quasars reveals no cool gas. We discuss how these results are complementary and provide support for the AGN unified model., Comment: 10 pages, 6 figures, accepted 01/11/2014 for publication in MNRAS

We present a code for modelling the ionization conditions of optically thin astrophysical gas structures. Given the gas hydrogen density, equilibrium temperature, elemental abundances, and the ionizing spectrum, the code solves the equilibrium ionization fractions and number densities for all ions from hydrogen to zinc. The included processes are photoionization, Auger ionization, direct collisional ionization, excitation auto-ionization, charge exchange ionization, two-body radiative recombination, dielectronic recombination, and charge exchange recombination. The ionizing spectrum can be generalized to include the ultraviolet background (UVB) and/or Starburst99 stellar populations of various masses, ages, metallicities, and distances. The ultimate goal with the code is to provide fast computation of the ionization conditions of gas in N-body + hydrodynamics cosmological simulations, in particular adaptive mesh refinement codes, in order to facilitate absorption line analysis of the simulated gas for comparison with observations. To this end, we developed a method to linearize the rate equations and efficiently solve the rate matrix with a minimum number of iterations. Comparing the code to Cloudy 13.03 (Ferland), we find that the hydrogen and helium ionization fractions and the metal species ionization corrections are in excellent agreement. We discuss the science drivers and plans for further development of the ionization code to a full radiative hydrodynamic routine that can be employed for processing the simulations. A stand-alone version of the code has been made publicly available (http://astronomy.nmsu.edu/cwc/Software/Ioncode/)., Comment: 17 pages, 7 figures; submitted to ApJ

We study the circumgalactic medium (CGM) of a z=0.54 simulated dwarf galaxy using hydroART simulations. We present our analysis methods, which emulate observations, including objective absorption line detection, apparent optical depth (AOD) measurements, Voigt profile (VP) decomposition, and ionization modeling. By comparing the inferred CGM gas properties from the absorption lines directly to the gas selected by low ionization HI and MgII, and by higher ionization CIV and OVI absorption, we examine how well observational analysis methods recover the "true" properties of CGM gas. In this dwarf galaxy, low ionization gas arises in sub-kiloparsec "cloud" structures, but high ionization gas arises in multiple extended structures spread over 100 kpc; due to complex velocity fields, highly separated structures give rise to absorption at similar velocities. We show that AOD and VP analysis fails to accurately characterize the spatial, kinematic, and thermal conditions of high ionization gas. We find that HI absorption selected gas and OVI absorption gas arise in totally distinct physical gas structures, calling into question current observational techniques employed to infer metallicities and the total mass of "warm-hot" CGM gas. We present a method to determine whether CIV and OVI absorbing gas is photo or collisionally ionized and whether the assumption of ionization equilibrium is sound. As we discuss, these and additional findings have strong implications for how accurately currently employed observational absorption line methods recover the true gas properties, and ultimately, our ability to understand the CGM and its role in galaxy evolution., Comment: 18 pages, 7 figures, revised version accepted to ApJ Jan 2015

We present the first observation of a galaxy (z=0.2) that exhibits metal-line absorption back-illuminated by the galaxy ("down-the-barrel") and transversely by a background quasar at a projected distance of 58 kpc. Both absorption systems, traced by MgII, are blueshifted relative to the galaxy systemic velocity. The quasar sight-line, which resides almost directly along the projected minor axis of the galaxy, probes MgI and MgII absorption obtained from Keck/LRIS and Lya, SiII and SiIII absorption obtained from HST/COS. For the first time, we combine two independent models used to quantify the outflow properties for down-the-barrel and transverse absorption. We find that the modeled down-the-barrel deprojected outflow velocities range between $V_{dtb}=45-255$ km/s. The transverse bi-conical outflow model, assuming constant-velocity flows perpendicular to the disk, requires wind velocities $V_{outflow}=40-80$ km/s to reproduce the transverse MgII absorption kinematics, which is consistent with the range of $V_{dtb}$. The galaxy has a metallicity, derived from H$\alpha$ and NII, of $[{\rm O/H}]=-0.21\pm0.08$, whereas the transverse absorption has $[{\rm X/H}]=-1.12\pm0.02$. The galaxy star-formation rate is constrained between $4.6-15$ M$_{\odot}$/yr while the estimated outflow rate ranges between $1.6-4.2$ M$_{\odot}$/yr and yields a wind loading factor ranging between $0.1-0.9$. The galaxy and gas metallicities, the galaxy-quasar sight-line geometry, and the down-the-barrel and transverse modeled outflow velocities collectively suggest that the transverse gas originates from ongoing outflowing material from the galaxy. The $\sim$1 dex decrease in metallicity from the base of the outflow to the outer halo suggests metal dilution of the gas by the time it reached 58 kpc., Comment: 6 pages, 4 figures. Accepted for publication in ApJL

We studied a sample of 14 galaxies (0.1 < z < 0.7) using HST/WFPC2 imaging and high-resolution HST/COS or HST/STIS quasar spectroscopy of Lya, Lyb, OVI1031, and OVI1037 absorption. The galaxies, having 10.8 < log(M/M_solar) < 12.2, lie within D = 300 kpc of quasar sightlines, probing out to D/R_vir = 3. When the full range of galaxy virial masses and D/R_vir of the sample are examined, 40% of the HI absorbing clouds can be inferred to be escaping their host halo. The fraction of bound clouds decreases as D/R_vir increases such that the escaping fraction is around 15% for D/R_vir < 1, around 45% for 1 < D/R_vir < 2, and around 90% for 2 < D/R_vir < 3. Adopting the median mass log(M/M_solar) = 11.5 to divide the sample into "higher" and "lower" mass galaxies, we find mass dependency for the hot CGM kinematics. To our survey limits, OVI absorption is found in only 40% of the HI clouds in and around lower mass halos as compared to 85% around higher mass halos. For D/R < 1, lower mass halos have an escape fraction of 65%, whereas higher mass halos have an escape fraction of 5%. For 1 < D/R_vir < 2, the escape fractions are 55% and 35% for lower mass and higher mass halos, respectively. For 2 < D/R_vir < 3, the escape fraction for lower mass halos is around 90%. We show that it is highly likely that the absorbing clouds reside within 4 virial radii of their host galaxies and that the kinematics are dominated by outflows. Our finding of "differential kinematics" is consistent with the scenario of "differential wind recycling" proposed by Oppenheimer et al. We discuss the implications for galaxy evolution, the stellar to halo mass function, and the mass metallicity relationship of galaxies., Comment: 23 pages, 19 figures, ApJ Accepted

We report the first measurements of MgII absorption systems associated with spectroscopically confirmed z~0.1 star-forming galaxies at projected distances of D<6kpc. We demonstrate the data are consistent with the well known anti-correlation between rest-frame MgII equivalent width, Wr(2796), and impact parameter, D, represented by a single log-linear relation derived by Nielsen et al. (MAGIICAT) that converges to ~2A at D=0kpc. Incorporating MAGIICAT, we find that the halo gas covering fraction is unity below D~25kpc. We also report that our D<6kpc absorbers are consistent with the Wr(2796) distributions of the Milky Way interstellar medium (ISM) and ISM+halo. In addition, quasar sight-lines of intermediate redshift galaxies with 6

In Churchill et al., we used halo abundance matching applied to 182 galaxies in the MgII Absorber-Galaxy Catalog (MAGIICAT, Nielsen et al.) and showed that the mean MgII 2796 equivalent width follows a tight inverse-square power law, W_r(2796) ~ (D/R_vir)^-2, with projected location relative to the galaxy virial radius and that the MgII absorption covering fraction is invariant with galaxy virial mass, M_h, over the range 10.7 < M_h/M_solar < 13.9. In this work, we explore multivariate relationships between W_r(2796), virial mass, impact parameter, virial radius, and the theoretical cooling radius that further elucidate self-similarity in the cool/warm (T=10^{4-4.5} K) circumgalactic medium (CGM) with virial mass. We show that virial mass determines the extent and strength of the MgII absorbing gas such that the mean W_r(2796) increases with virial mass at fixed distance while decreasing with galactocentric distance for fixed virial mass. The majority of the absorbing gas resides within D ~ 0.3 R_vir, independent of both virial mass and minimum absorption threshold; inside this region, and perhaps also in the region 0.3 < D/R_vir = 1, the mean W_r(2796) is independent of virial mass. Contrary to absorber-galaxy cross-correlation studies, we show there is no anti-correlation between W_r(2796) and virial mass. We discuss how simulations and theory constrained by observations fully support self-similarity of the cool/warm CGM via the physics governing star formation, gas-phase metal enrichment, recycling efficiency of galactic scale winds, filament and merger accretion, and overdensity of local environment as a function of virial mass., Comment: 25 pages plus full data table, 11 figures; Revised version accepted to The Astrophysical Journal (Oct 27, 2013)

Any successful model of galaxy formation needs to explain the low rate of star formation in the small progenitors of today's galaxies. This inefficiency is necessary for reproducing the low stellar-to-virial mass fractions, suggested by current abundance matching models. A possible driver of this low efficiency is the radiation pressure exerted by ionizing photons from massive stars. The effect of radiation pressure in cosmological, zoom-in galaxy formation simulations is modeled as a non-thermal pressure that acts only in dense and optically thick star-forming regions. We also include photoionization and photoheating by massive stars. The full photoionization of hydrogen reduces the radiative cooling in the $10^{4-4.5}$ K regime. The main effect of radiation pressure is to regulate and limit the high values of gas density and the amount of gas available for star formation. This maintains a low star formation rate of $\sim 1 \ {\rm M_\odot} \ {\rm yr}^{-1}$ in halos with masses about $10^{11} \ {M_\odot}$ at $z\simeq3$. Infrared trapping and photoionization/photoheating processes are secondary effects in this mass range. The galaxies residing in these low-mass halos contain only $\sim0.6\%$ of the total virial mass in stars, roughly consistent with abundance matching. Radiative feedback maintains an extended galaxy with a rising circular velocity profile., Comment: 18 pages, 11 figures, accepted version, new figure added, results and conclusions unchanged

We describe the MgII Absorber-Galaxy Catalog, MAGIICAT, a compilation of 182 spectroscopically identified intermediate redshift (0.07 < z < 1.1) galaxies with measurements of MgII 2796, 2803 absorption from their circumgalactic medium within projected distances of 200 kpc from background quasars. In this work, we present "isolated" galaxies, which are defined as having no spectroscopically identified galaxy within a projected distance of 100 kpc and a line of sight velocity separation of 500 km/s. We standardized all galaxy properties to the Lambda CDM cosmology and galaxy luminosities, absolute magnitudes, and rest-frame colors to the B- and K-band on the AB system. We present galaxy properties and rest-frame MgII equivalent width, Wr(2796), versus galaxy redshift. The well-known anti-correlation between Wr(2796) and quasar-galaxy impact parameter, D, is significant to the 8 sigma level. The mean color of MAGIICAT galaxies is consistent with an Sbc galaxy for all redshifts. We also present B- and K-band luminosity functions for different Wr(2796) and redshift subsamples: "weak absorbing" [Wr(2796) < 0.3 Ang], "strong absorbing" [Wr(2796) > 0.3 Ang], low redshift (z < zmed), and high redshift (z > zmed), where zmed = 0.359 is the median galaxy redshift. Rest-frame color B-K correlates with M_K at the 8 sigma level for the whole sample but is driven by the strong absorbing, high redshift subsample (6 sigma). Using M_K as a proxy for stellar mass and examining the luminosity functions, we infer that in lower stellar mass galaxies, MgII absorption is preferentially detected in blue galaxies and the absorption is more likely to be weak., Comment: 17 pages, 10 figures; accepted for publication in ApJ (September 11, 2013)

We have identified 469 MgII doublet systems having W_r >= 0.02 {\AA} in 252 Keck/HIRES and UVES/VLT quasar spectra over the redshift range 0.1 < z < 2.6. Using the largest sample yet of 188 weak MgII systems (0.02 {\AA} <= W_r < 0.3 {\AA}), we calculate their absorber redshift path density, dN/dz. We find clear evidence of evolution, with dN/dz peaking at z ~ 1.2, and that the product of the absorber number density and cross section decreases linearly with increasing redshift; weak MgII absorbers seem to vanish above z ~ 2.7. If the absorbers are ionized by the UV background, we estimate number densities of 10^6 - 10^9 per Mpc^3 for spherical geometries and 10^2 - 10^5 per Mpc^3 for more sheetlike geometries. We also find that dN/dz toward intrinsically faint versus bright quasars differs significantly for weak and strong (W_r >= 1.0 {\AA}) absorbers. For weak absorption, dN/dz toward bright quasars is ~ 25% higher than toward faint quasars (10 sigma at low redshift, 0.4 <= z <= 1.4, and 4 sigma at high redshift, 1.4 < z <= 2.34). For strong absorption the trend reverses, with dN/dz toward faint quasars being ~ 20% higher than toward bright quasars (also 10 sigma at low redshift and 4 sigma at high redshift). We explore scenarios in which beam size is proportional to quasar luminosity and varies with absorber and quasar redshifts. These do not explain dN/dz's dependence on quasar luminosity., Comment: 7 pages, 4 figures ApJ accepted

We examine the MgII absorbing circumgalactic medium (CGM) for the 182 intermediate redshift (0.072 < z < 1.120) galaxies in the "MgII Absorber-Galaxy Catalog" (MAGIICAT, Nielsen et al.). We parameterize the anti-correlation between equivalent width, Wr(2796), and impact parameter, D, with a log-linear fit, and show that a power law poorly describes the data. We find that higher luminosity galaxies have larger Wr(2796) at larger D (4.3 sigma). The covering fractions, f_c, decrease with increasing D and Wr(2796) detection threshold. Higher luminosity galaxies have larger f_c; no absorption is detected in lower luminosity galaxies beyond 100 kpc. Bluer and redder galaxies have similar f_c for D < 100 kpc, but for D > 100 kpc, bluer galaxies have larger f_c, as do higher redshift galaxies. The "absorption radius", R(L)=R*(L/L*)^{beta}$, which we examine for four different Wr(2796) detection thresholds, is more luminosity sensitive to the B-band than the K-band, more sensitive for redder galaxies than for bluer galaxies, and does not evolve with redshift for the K-band, but becomes more luminosity sensitive towards lower redshift for the B-band. These trends clearly indicate a more extended MgII absorbing CGM around higher luminosity, bluer, and higher redshift galaxies. Several of our findings are in conflict with other works. We address these conflicts and discuss the implications of our results for the low-ionization, intermediate redshift CGM., Comment: 14 pages, 7 figures; revised version contains additional galaxies and is accepted for publication in ApJ (August 5, 2013)