Probing the dynamical state, baryon content, and multiphase nature of
  galaxy clusters with bright background QSOs
  We have initiated a programme to study the physical/dynamical state of gas in
galaxy clusters and the impact of the cluster environment on gaseous halos of
individual galaxies using X-ray imaging and UV absorption line spectroscopy of
background QSOs. Here we report results from the analysis Chandra and
XMM-Newton archival data of five galaxy clusters with such QSOs, one of which
has an archival UV spectrum. We characterize the gravitational masses and
dynamical states, as well as the hot intracluster medium (ICM) properties of
these clusters. Most clusters are dynamically disturbed clusters based on the
X-ray morphology parameters, the X-ray temperature profiles, the large offset
between X-ray peak and brightest cluster galaxy (BCG). The baryon contents in
the hot ICM and stars of these clusters within $r_{500}$ are lower than the
values expected from the gravitational masses, according to the standard
cosmology. We also estimate column densities of the hot ICM along the
sightlines toward the background QSOs as well as place upper limits on the
warm-hot phase for the one sightline with existing UV observations. These
column densities, compared with those of the warm and warm-hot ICM to be
measured with UV absorption line spectroscopy, will enable us to probe the
relationship among various gaseous phases and their connection to the
heating/cooling and dynamical processes of the clusters. Furthermore, our
analysis of the archival QSO spectrum probing one cluster underscores the need
for high quality, targeted UV observations to robustly constrain the 10$^{5-6}$
K gas phase.
