Warm-hot Gas in X-ray Bright Galaxy Clusters and the H I-deficient
  Circumgalactic Medium in Dense Environments
  We analyze the intracluster medium (ICM) and circumgalactic medium (CGM) in 7
X-ray detected galaxy clusters using spectra of background QSOs (HST-COS/STIS),
optical spectroscopy of the cluster galaxies (MMT/Hectospec and SDSS), and
X-ray imaging/spectroscopy (XMM-Newton and Chandra). First, we report a very
low covering fraction of H I absorption in the CGM of these cluster galaxies,
f_c = 25% +25%/-15%, to stringent detection limits (log N(H I) < 13 cm^-2). As
field galaxies have an H I covering fraction of ~100% at similar radii, the
dearth of CGM H I in our data indicates that the cluster environment has
effectively stripped or overionized the gaseous halos of these cluster
galaxies. Second, we assess the contribution of warm-hot (10^5 - 10^6 K) gas to
the ICM as traced by O VI and broad Ly-alpha (BLA) absorption. Despite the high
signal-to-noise of our data, we do not detect O VI in any cluster, and we only
detect BLA features in the QSO spectrum probing one cluster. We estimate that
the total column density of warm-hot gas along this line of sight totals to ~3%
of that contained in the hot T > 10^7 K X-ray emitting phase. Residing at high
relative velocities, these features may trace pre-shocked material outside the
cluster. Comparing gaseous galaxy halos from the low-density 'field' to galaxy
groups and high-density clusters, we find that the CGM is progressively
depleted of H I with increasing environmental density, and the CGM is most
severely transformed in galaxy clusters. This CGM transformation may play a key
role in environmental galaxy quenching.
