Abstract
We analyze the intracluster medium (ICM) and circumgalactic medium (CGM) in 7
X-ray detected galaxy clusters using spectra of background QSOs from HST/COS
and HST/STIS, optical spectroscopy of the cluster galaxies from MMT/Hectospec
and SDSS, and X-ray imaging/spectroscopy from XMM-Newton and Chandra. Optical
spectroscopy reveals many galaxies at small impact parameters (<300 kpc) to the
QSO sightlines and within ~1000 km/s of the cluster redshifts; we report a very
low covering fraction of H I absorption in the CGM of these cluster galaxies,
f_c = 18% +14%/-9%, to stringent detection limits (log N(HI) < 13 cm^-2) in
most cases. As field galaxies have H I covering fractions of ~100% at similar
radii, the dearth of CGM H I in our data indicates that the cluster environment
has effectively stripped or gravitationally heated and overionized the gaseous
halos of these member 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, which would potentially bring the cluster baryon content closer to
the universal baryon mass fraction (~17%). Despite the high S/N 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
material in the warm-hot phase along this line of sight totals to ~3% of that
contained in the hot T > 10^7 K X-ray emitting phase. These features may trace
pre-shocked material outside the cluster. Comparing halo gas properties in
regions ranging 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, where galaxy clusters are extreme sites where the CGM is
most severely transformed. This transformation may play a key role in
environmental galaxy quenching.
Description
[1705.05892] Warm-hot Gas in X-ray Bright Galaxy Clusters and the H I-deficient Circumgalactic Medium in Dense Environments
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