We report a bimodality in the azimuthal angle distribution of gas around galaxies as traced by Mg II absorption: Halo gas prefers to exist near the projected galaxy major and minor axes. The bimodality is demonstrated by computing the mean azimuthal angle probability distribution function using 88 spectroscopically confirmed Mg II absorption-selected galaxies [W r (2796) ≥ 0.1 Å] and 35 spectroscopically confirmed nonabsorbing galaxies [W r (2796) < 0.1 Å] imaged with HST and SDSS. The azimuthal angle distribution for non-absorbers is flat, indicating no azimuthal preference for gas characterized by W r (2796) < 0.1 Å. We find that blue star-forming galaxies clearly drive the bimodality while red passive galaxies may exhibit an excess along their major axis. These results are consistent with galaxy evolution scenarios where star-forming galaxies accrete new gas, forming new stars and producing winds, while red galaxies exist passively due to reduced gas reservoirs. We further compute an azimuthal angle dependent Mg II absorption covering fraction, which is enhanced by as much as 20−30% along the major and minor axes. The W r (2796) distribution for gas along the major axis is likely skewed toward weaker Mg II absorption than for gas along the projected minor axis. These combined results are highly suggestive that the bimodality is driven by gas accreted along the galaxy major axis and outflowing along the galaxy minor axis. Adopting these assumptions, we find that the opening angle of outflows and inflows to be 100 • and 40 • , respectively. We find the probability of detecting outflows is ∼60%, implying that winds are more commonly observed.

We examine the Mg II absorbing circumgalactic medium (CGM) for the 182 intermediate redshift (0.072 ≤ z ≤ 1.120) galaxies in the "Mg II Absorber-Galaxy Catalog" (MAGIICAT, Nielsen et al.). We parameterize the anti-correlation between equivalent width, W r (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 W r (2796) at larger D (4.3 σ). The covering fractions, f c , decrease with increasing D and W r (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 * ) β , which we examine for four different W r (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 Mg II 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.

We describe the Mg II Absorber-Galaxy Catalog, MAGIICAT, a compilation of 182 spectroscopically identified intermediate redshift (0.07 ≤ z ≤ 1.1) galaxies with measurements of Mg II λλ2796, 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 −1 . We standardized all galaxy properties to the ΛCDM 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 Mg II equivalent width, W r (2796), versus galaxy redshift. The well-known anti-correlation between W r (2796) and quasar-galaxy impact parameter, D, is significant to the 8 σ 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 W r (2796) and redshift subsamples: "weak absorbing" [W r (2796) < 0.3 Å], "strong absorbing" [W r (2796) ≥ 0.3 Å], low redshift (z < z ), and high redshift (z ≥ z ), where z = 0.359 is the median galaxy redshift. Rest-frame color B − K correlates with M K at the 8 σ level for the whole sample but is driven by the strong absorbing, high redshift subsample (6 σ). Using M K as a proxy for stellar mass and examining the luminosity functions, we infer that in lower stellar mass galaxies, Mg II absorption is preferentially detected in blue galaxies and the absorption is more likely to be weak.

We report a bimodality in the azimuthal angle (Φ) distribution of gas around galaxies traced by O VI absorption. We present the mean Φ probability distribution function of 29 HST-imaged O VI absorbing (EW>0.1 Å) and 24 non-absorbing (EW<0.1 Å) 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 M ⊙ ), star forming (∼ 6.9 M ⊙ yr −1 ), sub-L * (∼ 0.5L * 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 • ) and the azimuthal angle (Φ = 73 • ) 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 O VI (log N = 15.16 ± 0.04, ∆v 90 = 419 km s −1 ) and N V (log N = 14.69 ± 0.07, ∆v 90 = 285 km s −1 ) 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 Lyβ profile, the non-detection of S IV absorption, and the presence of strong C IV absorption in the low-resolution FOS spectrum we rule out equilibrium/non-equilibrium collisional ionization models. The lowionization 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 ∼ 2 × 10 10 M ⊙ , a mass-flow rate of ∼ 54 M ⊙ yr −1 , a kinetic luminosity of ∼ 9 × 10 41 erg s −1 , 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.

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 investigate the dependence of gas kinematics and column densities in the Mg II-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 < z gal < 1.0, imaged with the Hubble Space Telescope, are probed by background quasars within a projected distance of 20 < D < 110 kpc. From the high-resolution (∆v 6.6 km s −1 ) quasar spectra, we quantify the extent of the absorber velocity structure with pixel-velocity twopoint correlation functions. Absorbers with the largest velocity dispersions are associated with blue, face-on (i < 57 • ) galaxies probed along the projected minor axis (Φ ≥ 45 • ), while those with the smallest velocity dispersions belong to red, face-on galaxies along the minor axis. The velocity structure is similar for edge-on (i ≥ 57 • ) galaxies regardless of galaxy color or azimuthal angle, for red galaxies with azimuthal angle, and for blue and red galaxies probed along the projected major axis (Φ < 45 • ). The cloud column densities for face-on galaxies and red galaxies are smaller than for edge-on galaxies and blue galaxies, respectively. These results are consistent with biconical outflows along the minor axis for star-forming galaxies and accreting and/or rotating gas, which is most easily observed in edge-on galaxies probed along the major axis. Gas entrained in outflows may be fragmented with large velocity dispersions, while gas accreting onto or rotating around galaxies may be more coherent due to large path lengths and smaller velocity dispersions. Quiescent galaxies may exhibit little-to-no outflows along the minor axis, while accretion/rotation may exist along the major axis.

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.