We present basic data and modeling for a survey of the cool, photo-ionized Circum-Galactic Medium (CGM) of low-redshift galaxies using far-UV QSO absorption line probes. This survey consists of "targeted" and "serendipitous" CGM subsamples, originally described in Stocke et al. (2013, Paper 1). The targeted subsample probes low-luminosity, late-type galaxies at z < 0.02 with small impact parameters ( ρ = 71 kpc), and the serendipitous subsample probes higher luminosity galaxies at z 0.2 with larger impact parameters ( ρ = 222 kpc). HST and FUSE UV spectroscopy of the absorbers and basic data for the associated galaxies, derived from ground-based imaging and spectroscopy, are presented. We find broad agreement with the COS-Halos results, but our sample shows no evidence for changing ionization parameter or hydrogen density with distance from the CGM host galaxy, probably because the COS-Halos survey probes the CGM at smaller impact parameters. We find at least two passive galaxies with H I and metal-line absorption, confirming the intriguing COS-Halos result that galaxies sometimes have cool gas halos despite no on-going star formation. Using a new methodology for fitting H I absorption complexes, we confirm the CGM cool gas mass of Paper 1, but this value is significantly smaller than found by the COS-Halos survey. We trace much of this difference to the specific values of the low-z meta-galactic ionization rate assumed. After accounting for this difference, a best-value for the CGM cool gas mass is found by combining the results of both surveys to obtain log (M/M ) = 10.5 ± 0.3, or ∼ 30% of the total baryon reservoir of an L ≥ L * , star-forming galaxy.

To establish the connection between galaxies and UV-detected absorption systems in the local universe, a deep (g ≤ 20) and wide (∼ 20 radius) galaxy redshift survey is presented around 47 sight lines to UV-bright AGN observed by the Cosmic Origins Spectrograph (COS). Specific COS science team papers have used this survey to connect absorbers to galaxies, groups of galaxies, and large-scale structures, including voids. Here we present the technical details of the survey and the basic measurements required for its use, including redshifts for individual galaxies and uncertainties determined collectively by spectral class (emission-line, absorption-line, and composite spectra) and completeness for each sight line as a function of impact parameter and magnitude. For most of these sight lines the design criteria of > 90% completeness over a > 1 Mpc region down to 0.1 L * luminosities at z ≤ 0.1 allows a plausible association between low-z absorbers and individual galaxies. Lyα covering fractions are computed to approximate the star-forming and passive galaxy populations using the spectral classes above. In agreement with previous results, the covering fraction of star-forming galaxies with L ≥ 0.3 L * is consistent with unity inside one virial radius and declines slowly to > 50% at 4 virial radii. On the other hand, passive galaxies have lower covering fractions (∼ 60%) and a shallower decline with impact parameter, suggesting that their gaseous halos are patchy but have a larger scale-length than star-forming galaxies. All spectra obtained by this project are made available electronically for individual measurement and use.

In preparation for a Hubble Space Telescope (HST) observing project using the Cosmic Origins Spectrograph (COS), the positions of all AGN targets having high-S/N far-UV G130M spectra were cross-correlated with a large catalog of low-redshift galaxy groups homogenously selected from the spectroscopic sample of the Sloan Digital Sky Survey (SDSS). Searching for targets behind only those groups at z = 0.1-0.2 (which places the O VI doublet in the wavelength region of peak COS sensitivity) we identified only one potential S/N = 15-20 target, FBQS 1010+3003. An O VI-only absorber was found in its G130M spectrum at z = 0.11326, close to the redshift of a foreground small group of luminous galaxies at z = 0.11685. Because there is no associated Lyα absorption, any characterization of this absorber is necessarily minimal; however, the O VI detection likely traces "warm" gas in collisional ionization equilibrium at T ≈ 3 × 10 5 K. While this discovery is consistent with being interface gas between cooler, photoionized clouds and a hotter intra-group medium, it could also be warm, interface gas associated with the circum-galactic medium (CGM) of the single closest galaxy. In this case a detailed analysis of the galaxy distribution (complete to 0.2 L * ) strongly favors the individual galaxy association. This analysis highlights the necessity of both high-S/N > 20 COS data and a deep galaxy redshift survey of the region in order to test more rigorously the association of O VI-absorbing gas with a galaxy group. A Cycle 23 HST/COS program currently is targeting 10 UV-bright AGN behind 12 low-redshift galaxy groups to test the warm, group gas hypothesis.

We investigate the association between galaxies and metal-enriched and metal-deficient absorbers in the local universe (z < 0.16) using a large compilation of FUV spectra of bright AGN targets observed with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope. In this homogeneous sample of 18 O VI detections at N O VI ≥ 13.5 cm −2 and 18 non-detections at N O VI < 13.5 cm −2 using Lyα absorbers with N H I ≥10 14 cm −2 , the maximum distance O VI extends from galaxies of various luminosities is ∼ 0.6 Mpc, or ∼ 5 virial radii, confirming and refining earlier results. This is an important value that must be matched by numerical simulations, which input the strength of galactic winds at the sub-grid level. We present evidence that the primary contributors to the spread of metals into the circum-and intergalactic media are sub-L * galaxies (0.25L * < L < L * ). The maximum distances that metals are transported from these galaxies is comparable to, or less than, the size of a group of galaxies. These results suggest that, where groups are present, the metals produced by the group galaxies do not leave the group. Since many O VI non-detections in our sample occur at comparably close impact parameters as the metal-bearing absorbers, some more pristine intergalactic material appears to be accreting onto groups where it can mix with metal-bearing clouds.

A small survey of the UV-absorbing gas in 12 low-z galaxy groups has been conducted using the Cosmic Origins Spectrograph (COS) on-board the Hubble Space Telescope (HST). Targets were selected from a large, homogeneously-selected sample of groups found in the Sloan Digital Sky Survey (SDSS). A critical selection criterion excluded sight lines that pass close (< 1.5 virial radii) to a group galaxy, to ensure absorber association with the group as a whole. to characterize these 10 13.5 to 10 14.5 M groups, the most massive of which are highly-virialized with numerous early-type galaxies (ETGs). This sample also includes two spiral-rich groups, not yet fully-virialized. At group-centric impact parameters of 0.3-2 Mpc, these S/N = 15-30 spectra detected H I absorption in 7 of 12 groups; high (O VI) and low (Si III) ion metal lines are present in 2/3 of the absorption components. None of the three most highly-virialized, ETG-dominated groups are detected in absorption. Covering fractions 50% are seen at all impact parameters probed, but do not require large filling factors despite an enormous extent. Unlike halo clouds in individual galaxies, group absorbers have radial velocities which are too low to escape the group potential well without doubt. This suggests that these groups are "closed boxes" for galactic evolution in the current epoch. Evidence is presented that the cool and warm group absorbers are not a pervasive intra-group medium (IGrM), requiring a hotter (T ∼ 10 6 to 10 7 K) IGrM to be present to close the baryon accounting.

Most of the baryons in L* galaxies are unaccounted for and are predicted to lie in hot gaseous halos (T ∼ 106.5 K) that may extend beyond R 200. A hot gaseous halo will produce a thermal Sunyaev–Zeldovich signal that is proportional to the product of the gas mass and the mass-weighted temperature. To best detect this signal, we used a Needlet Independent Linear Combination all-sky Planck map that we produced from the most recent Planck data release, also incorporating WMAP data. The sample is 12 L* spiral galaxies with distances of 3−10 Mpc, which are spatially resolved so that contamination from the optical galaxy can be excluded. One galaxy, NGC 891, has a particularly strong SZ signal, and when excluding it, the stack of 11 galaxies is detected at about 4σ (declining with radius) and is extended to at least 250 kpc (≈R 200) at >99% confidence. The gas mass within a spherical volume to a radius of 250 kpc is 9.8 ± 2.8 × 1010 M ⊙, for T avg = 3 × 106 K. This is about 30% of the predicted baryon content of the average galaxy (3.1 × 1011 M ⊙), and about equal to the mass of stars, disk gas, and warm halo gas. The remaining missing baryons (≈1.4 × 1011 M ⊙, 40%–50% of the total baryon content) are likely to be hot and extend to the 400–500 kpc volume, if not beyond. The result is higher than predictions, but within the uncertainties.

SZ scaling relations have been used to test the self-similar prediction for massive galaxy clusters, but little attention has been given to individual galaxy groups. We investigate the scaling relations of galaxy groups and clusters near the North Ecliptic Pole using X-ray and SZ observations. This region of the sky is where both the ROSAT and Planck satellites achieved their deepest observations, permitting the investigation of lower mass systems. Our sample consists of 62 X-ray detected groups and clusters, spanning a mass range of 10 13.4 M < M 500 < 10 15 M and redshifts of 0.03 z 0.82. We extract the total SZ flux from unresolved Planck data and estimate the fraction of the SZ flux within R 500 assuming two different pressure profiles. The SZ scaling relations were derived using a Bayesian technique that accounts for censored data. We find a power law slope of 1.73 +0.19 −0.18 for the Y SZ − M 500 relation which is consistent with the self-similar prediction of 5/3. The slope of 0.89 +0.09 −0.08 for the Y SZ − L X,500 relation is in agreement with other observational studies but not the self-similar prediction of 5/4, and the Y SZ − Y X relation lies below the 1:1 relation when the slope is fixed to unity. The determined scaling relations are dependent on the selected pressure profile, so resolved data are needed to determine the effects of AGN feedback. In addition, we find a number of potential cluster candidates in the Planck Compton maps that were not identified in our X-ray sample.

Many of the baryons in galaxy groups are thought to have been driven out to large distances (≳R 500) by feedback, but there are few constraining observations of this extended gas. This work presents the resolved Sunyaev–Zel’dovich (SZ) profiles for a stacked sample of 10 nearby galaxy groups within the mass range log 10 ( M 500 [ M ⊙ ] ) = 13.6 – 13.9 . We measured the SZ profiles using the publicly available y-map from the Planck Collaboration as well as our own y-maps constructed from more recent versions of Planck data. The y-map extracted from the latest data release yielded a significant SZ detection out to 3 R 500. In addition, the stacked profile from these data was consistent with simulations that included AGN feedback. Our best-fit model using the latest Planck data suggested a baryon fraction ≈5.6% within R 500. This is significantly lower than the cosmic value of ≈16%, supporting the idea that baryons have been driven to large radii by AGN feedback. Lastly, we discovered a significant (∼3σ) “bump” feature near ∼2 R 500 that is most likely the signature of internal accretion shocks.