Suzaku observations of subhalos in the Coma cluster

TL;DR

This study uses Suzaku X-ray observations to analyze three subhalos in the Coma cluster, revealing their gas properties, temperature differences, and the effects of ram pressure and Kelvin-Helmholtz instability on gas stripping.

Contribution

First detailed X-ray analysis of multiple subhalos in the Coma cluster, linking weak-lensing data with gas properties and dynamical effects.

Findings

Subhalo 'ID 1' has a compact X-ray excess with a gas mass to weak-lensing mass ratio of about 0.001.

Subhalo 'ID 32' shows an offset X-ray excess with a lower temperature (~0.5 keV) and similar gas mass ratio.

No significant X-ray excess detected in subhalo 'ID 2'.

Abstract

We observed three massive subhalos in the Coma cluster with {\it Suzaku}. These subhalos, labeled "ID 1", "ID 2", and "ID 32", were detected with a weak-lensing survey using the Subaru/Suprime-Cam (Okabe et al. 2014a), and are located at the projected distances of 1.4 $r_{500}$, 1.2 $r_{500}$, and 1.6 $r_{500}$ from the center of the Coma cluster, respectively. The subhalo "ID 1" has a compact X-ray excess emission close to the center of the weak-lensing mass contour, and the gas mass to weak-lensing mass ratio is about 0.001. The temperature of the emission is about 3 keV, which is slightly lower than that of the surrounding intracluster medium (ICM) and that expected for the temperature vs. mass relation of clusters of galaxies. The subhalo "ID 32" shows an excess emission whose peak is shifted toward the opposite direction from the center of the Coma cluster. The gas mass to weak-lensing mass ratio is also about 0.001, which is significantly smaller than regular galaxy groups. The temperature of the excess is about 0.5 keV and significantly lower than that of the surrounding ICM and far from the temperature vs. mass relation of clusters. However, there is no significant excess X-ray emission in the "ID 2" subhalo. Assuming an infall velocity of about 2000 $\rm km~s^{-1}$, at the border of the excess X-ray emission, the ram pressures for "ID 1" and "ID 32" are comparable to the gravitational restoring force per area. We also studied the effect of the Kelvin-Helmholtz instability to strip the gas. Although we found X-ray clumps associated with the weak-lensing subhalos, their X-ray luminosities are much lower than the total ICM luminosity in the cluster outskirts.