Dark Matter Subhalos and the X-ray Morphology of the Coma Cluster
  Structure formation models predict that clusters of galaxies contain numerous
massive subhalos. The gravity of a subhalo in a cluster compresses the
surrounding intracluster gas and enhances its X-ray emission. We present a
simple model, which treats subhalos as slow moving and gasless, for computing
this effect. Recent weak lensing measurements by Okabe et al. have determined
masses of ~ 10^13 solar masses for three mass concentrations projected within
300 kpc of the center of the Coma Cluster, two of which are centered on the
giant elliptical galaxies NGC 4889 and NGC 4874. Adopting a smooth spheroidal
beta-model for the gas distribution in the unperturbed cluster, we model the
effect of these subhalos on the X-ray morphology of the Coma Cluster, comparing
our results to Chandra and XMM-Newton X-ray data. The agreement between the
models and the X-ray morphology of the central Coma Cluster is striking. With
subhalo parameters from the lensing measurements, the distances of the three
subhalos from the Coma Cluster midplane along our line of sight are all tightly
constrained. Using the model to fit the subhalo masses for NGC 4889 and NGC
4874 gives 9.1 x 10^12 and 7.6 x 10^12 solar masses, respectively, in good
agreement with the lensing masses. These results lend strong support to the
argument that NGC 4889 and NGC 4874 are each associated with a subhalo that
resides near the center of the Coma Cluster. In addition to constraining the
masses and 3-d location of subhalos, the X-ray data show promise as a means of
probing the structure of central subhalos.
