X-ray Study of the Dark Matter Distribution in Clusters of Galaxies with Chandra

Abstract

We study the total gravitating mass distribution in the central region of 23 clusters of galaxies with Chandra. Using a new deprojection technique, we measure the temperature and gas density in the very central region of the clusters as a function of radius without assuming any particular models. Under the assumptions of hydrostatic equilibrium and spherical symmetry, we obtain the deprojected mass profiles of these clusters. The mass profiles are nicely scalable with a characteristic radius ($r_{200}$) and mass ($M_{200}$) on the large scale of $r>0.1r_{200}$. In contrast, the central ($r<0.1r_{200}$) mass profiles have a large scatter even after the scaling. The inner slope $\alpha$ of the total mass density profile ($\rho(r) \propto r^{-\alpha}$) is derived from the slope of the integrated mass profile. The values of the inner slope $\alpha$ at the radius of $0.02r_{200}$ ($\alpha_0$) span a wide range from 0 to 1.2. For 6 out of 20 clusters, $\alpha_0$ is lower than unity at a 90 % confidence level. CDM simulations predict that the inner slope $\alpha$ is in the range $1<\alpha<2$, which is inconsistent with our results. We also found that the gas fraction near the center of a cluster has a negative correlation with $\alpha_0$. Our result suggests that the gas-rich clusters in the central region tend to have a flat core.