X-ray mapping the outer regions of galaxy clusters at z= 0.23 and 0.45
  The thermal, chemical, and kinematic properties of the potentially
multi-phase circum/inter-galactic medium at the virial radii of galaxy clusters
remain largely uncertain. We present an X-ray study of Abell 2246 and GMBCG
J255.34805+64.23661 (z=0.23 and 0.45), two foreground clusters of the UV-bright
QSO HS 1700+6416, based on 240 ks Chandra/ACIS-I observations. We detect
enhanced diffuse X-ray emission to the projected distances beyond r_{200} radii
of these two clusters. The large-scale X-ray emission is consistent with being
azimuthally symmetric at the projected radii of the QSO (0.36 and 0.8 times the
radii of the two clusters). Assuming a spherical symmetry, we obtain the
de-projected temperature and density profiles of the X-ray-emitting gas.
Excluding the cool cores that are detected, we find that the mean temperature
of the hot gas is about 4.0 keV for Abell 2246 and 5.5 keV for GMBCG
J255.34805+64.23661, although there are indications for temperature drop at
large radii. From these results, we can estimate the density and pressure
distributions of the hot gas along the QSO sightline. We further infer the
radial entropy profile of Abell 2246 and compare it with the one expected from
purely gravitational hierarchical structure formation. This comparison shows
that the ICM in the outer region of the clusters is likely in a clumpy and
multi-phased state. These results, together with the upcoming HST/COS
observations of the QSO sightline, will enable a comprehensive investigation of
the multi-phase medium associated with the clusters.
