Dark Matter Subhalos and the X-ray Morphology of the Coma Cluster. (arXiv:1302.1917v1 [astro-ph.CO])

Dark Matter Subhalos and the X-ray Morphology of the Coma Cluster. (arXiv:1302.1917v1 [astro-ph.CO]):
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. (2010) 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.