By comparing Mg II absorption in the circumgalactic medium (CGM) of group environments to isolated galaxies, we investigated the impact of environment on the CGM. A Mg II 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 −1 . We compiled a sample of 29 group environments consisting of 74 galaxies (2 − 5 galaxies per group) at 0.113 < z gal < 0.888. The group absorber median equivalent width ( W r (2796) = 0.65 ± 0.13 Å) and covering fraction ( f c = 0.89 +0.05 −0.09 ) are larger than isolated absorbers (1.27σ and 2.2σ, respectively) but median column densities are statistically consistent. A pixel-velocity two-point correlation function analysis shows that group environment kinematics are statistically comparable to isolated environments (0.8σ), but with more power for high velocity dispersions similar to outflow kinematics. Group absorbers display more optical depth at larger velocities. A superposition model in which multiple galaxies contribute to the observed gas matches larger equivalent width group absorbers, but overpredicts the kinematics significantly due to large velocity separations between member galaxies. Finally, galaxy-galaxy groups (similar member galaxy luminosities) may have larger absorber median equivalent widths (1.7σ) and velocity dispersions (2.5σ) than galaxy-dwarf groups (disparate luminosities). We suggest the observed gas is coupled to the group rather than individual galaxies, forming an intragroup medium. Gas may be deposited into this medium by multiple galaxies via outflowing winds undergoing an intergalactic transfer between member galaxies or from tidal stripping of interacting members.

We present a study comparing O VI λλ1031, 1037 doublet absorption found towards group galaxy environments with that of isolated galaxies. The O VI 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 −1 and located within 350 kpc (projected) of a background quasar sightline. We identified a total of six galaxy groups associated with O VI absorption W r > 0.06 Å that have a median redshift of z gal = 0.1669 and a median impact parameter of D = 134.1 kpc. An additional 12 non-absorbing groups were identified with a median redshift of z gal = 0.2690 and a median impact parameter of D = 274.0 kpc. We find the average equivalent width to be smaller for group galaxies than for isolated galaxies (3σ). 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 O VI in the CGM of group galaxies is significantly narrower than that of isolated galaxies (10σ). 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 O VI to be further ionised. The remaining O VI likely exists at the interface between hot, diffuse gas and cooler regions of the CGM.

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 Hubble Space Telescope (HST)/COS and from Keck/HIRES or Very Large Telescope/UVES, we measure column densities of, or determine limits on, CGM absorption lines. We then use a Markov Chain Monte Carlo approach with Cloudy to estimate the metallicity of cool (T∼10 4 K) CGM gas. We also use HST images to determine hostgalaxy inclination and quasar-galaxy azimuthal angles. Our sample spans a H Icolumn density range of 13.8 cm −2 < N log H I <19.9 cm −2. We find (1) while the metallicity distribution appears bimodal, a Hartigan dip test cannot rule out a unimodal distribution (0.4σ). (2) CGM metallicities are independent of halo mass, spanning three orders of magnitude at a fixed halo mass. (3) The CGM metallicity does not depend on the galaxy azimuthal and inclination angles regardless of H Icolumn density, impact parameter, and galaxy color. (4) The 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 lowmetallicity 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.

We present the first galaxy-O VI absorption kinematic study for 20 absorption systems (EW>0.1 Å) associated with isolated galaxies (0.15 ≤ z ≤ 0.55) that have accurate redshifts and rotation curves obtained using Keck/ESI. Our sample is split into two azimuthal angle bins: major axis (Φ < 25 • ) and minor axis (Φ > 33 • ). O VI 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 Mg II absorption. O VI along the minor axis could be modeled by accelerating outflows but only for small opening angles, while the majority of the O VI is decelerating. Along both axes, stacked O VI profiles reside at the galaxy systemic velocity with the absorption kinematics spanning the entire dynamical range of their galaxies. The O VI found in AMR cosmological simulations exists within filaments and in halos of ∼50 kpc surrounding galaxies. Simulations show that major axis O VI 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 O VI 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 O VI throughout the halo. We conclude that O VI alone does not serve as a useful kinematic indicator of gas accretion, outflows or star-formation and likely best probes the halo virial temperature.

We present ISM and CGM metallicities for 25 absorption systems associated with isolated star-forming galaxies ( z = 0.28) with 9.4≤log(M * /M ⊙ )≤10.9 and with absorption detected within 200 kpc. Galaxy ISM metallicities were measured using Hα/[N II] emission lines from Keck/ESI spectra. CGM single-phase lowionization metallicities were modeled using MCMC and Cloudy analysis of absorption from HST/COS and Keck/HIRES or VLT/UVES quasar spectra. We find that the star-forming galaxy ISM metallicities follow the observed stellar mass metallicity relation (1σ scatter 0.19 dex). CGM metallicity shows no dependence with stellar mass and exhibits a scatter of ∼2 dex. All CGM metallicities are lower than the galaxy ISM metallicities and are offset by log(dZ) = −1.17 ± 0.11. There is no obvious metallicity gradient as a function of impact parameter or virial radius (< 2.3σ significance). There is no relationship between the relative CGM-galaxy metallicity and azimuthal angle. We find the mean metallicity differences along the major and minor axes are −1.13±0.18 and −1.23±0.11, respectively. Regardless of whether we examine our sample by low/high inclination or low/high impact parameter, or low/high N(H I), we do not find any significant relationship with relative CGM-galaxy metallicity and azimuthal angle. We find that 10/15 low column density systems (logN(H I)< 17.2) reside along the galaxy major axis while high column density systems (logN(H I)≥ 17.2) reside along the minor axis. This suggest N(H I) 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. On the-other-hand, 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.

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 < z gal < 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 non-virialized 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 faceon minor axis gas has a smoothly decreasing optical depth distribution out to large normalized absorbergalaxy velocities, suggestive of decelerating outflowing gas. Accreting gas signatures are not observed due 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.

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 Ly α emission from a 1.7L * galaxy at z gal = 2.0711 associated with a Lyman limit system with weak Mgii (W r (2796) = 0.24 Å) in quasar field J143040+014939. The galaxy is star-forming (SFR FUV = 37.8 M yr −1 ) and clumpy: either an edge-on disk (i = 85 • ) 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 (Φ = 89 • ). From photoionization modeling of the absorption system, we infer a total line-of-sight CGM metallicity of [Si/H] = −1.5 +0.4 −0.3 . The absorption system is roughly kinematically symmetric about z gal , with a full Mg ii velocity spread of ∼ 210 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 out = 109−588 km s −1 for half opening angles of θ 0 = 14 • − 75 • . Assuming a constant V out , it would take on average t out ∼ 111 − 597 Myr for the gas to reach 66 kpc. The outflow is energetic, with a mass outflow rate of Ṁout < 52±37 M yr −1 and mass loading factor of η < 1.4±1.0. We aim to build a sample of ∼ 50 Mgii absorber-galaxy pairs at this epoch to better understand gas flows when they are most actively building galaxies.

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 H i (EWr&lt;0.02 Å, log(N(H i)/cm−2)&lt;12.6) and a range of low and high ionisation 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 SFR (1.1 M⊙ yr−1), SSFR (1.5 × 10−10 yr−1) and ΣSFR (0.06 M⊙ 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 H i absorption-selected galaxies, we find that quiescent galaxies with log(SSFR/yr−1) &lt; −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) &gt; −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) &gt; −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 ± 1 Gyr. G1547 provides a unique perspective into the external mechanisms that could explain the migration of galaxies into the green valley.