We investigated the dynamical structure of 53 elliptical galaxies, based on the { \it Chandra} archival X-ray data. In X-ray luminous galaxies, a temperature increases with radius and a gas density is systematically higher at the optical outskirts, indicating a presence of a significant amount of the group-scale hot gas. In contrast, X-ray dim galaxies show a flat or declining temperature profile against radius and the gas density is relatively lower at the optical outskirts. Thus it is found that X-ray bright and faint elliptical galaxies are clearly distinguished by the temperature and gas density profile. The mass profile is well scaled by a virial radius $r_{ 200}$ rather than an optical-half radius $r_e$, and is quite similar at $(0.001-0.03)r_{ 200}$ between X-ray luminous and dim galaxies, and smoothly connects to those of clusters of galaxies. At the inner region of $(0.001-0.01)r_{ 200}$ or $(0.1-1)r_e$, the mass profile well traces a stellar mass with a constant mass-to-light ratio of $M/L_{ \rm B}=3-10(M_{ \odot}/L_{ \odot})$. $M/L_{ \rm B}$ ratio of X-ray bright galaxies rises up steeply beyond $0.01r_{ 200}$, and thus requires a presence of massive dark matter halo. From the deprojection analysis combined with the { \it XMM-Newton} data, we found that X-ray dim galaxies, NGC 3923, NGC 720, and IC 1459, also have a high $M/L_{ \rm B}$ ratio of 20--30 at 20 kpc, comparable to that of X-ray luminous galaxies. Therefore, dark matter is indicated to be common in elliptical galaxies, and their distribution almost follows the NFW profile, as well as galaxy clusters.
Categories: astro-ph