Chandra Studies of the X-ray Gas Properties of Fossil Systems
  We study ten galaxy groups and clusters suggested in the literature to be
"fossil system (FS)" based on \chandra\ observations. According to the
$M_{500}-T$ and $L_{\rm X}-T$ relations, the gas properties of FSs are not
physically distinct from ordinary galaxy groups or clusters. We also first
study the $f_{\rm gas,~2500}-T$ relation and find that the FS exhibits same as
ordinary systems. The gas densities of FSs within $0.1r_{200}$, are $\sim
10^{-3}$ cm$^{-3}$, which is the same order as galaxy clusters. The entropies
within $0.1r_{200}$ ($S_{0.1r_{200}}$) of FSs are systematically lower than
those in ordinary galaxy groups which is consistent with previous report, but
we find their $S_{0.1r_{200}}-T$ relation is more similar to galaxy clusters.
The derived mass profiles of FSs are consistent with the Navarro, Frenk, \&
White model in $(0.1-1)r_{200}$, and the relation between scale radius $r_{\rm
s}$ and characteristic mass density $ta_{\rm c}$ indicates the self-similarity
of dark matter halos of FSs. The range of $r_{\rm s}$ and $ta_{\rm c}$ of FSs
are also close to those of galaxy clusters. Therefore, FSs share more common
characteristics with galaxy clusters. The special birth place of the FS makes
it as a distinct galaxy system type.
