Scaling Mass Profiles around Elliptical Galaxies Observed withChandraandXMM‐Newton

We investigated the dynamical structure of 53 elliptical galaxies, based onthe {\it Chandra} archival X-ray data. In X-ray luminous galaxies, atemperature increases with radius and a gas density is systematically higher atthe optical outskirts, indicating a presence of a significant amount of thegroup-scale hot gas. In contrast, X-ray dim galaxies show a flat or decliningtemperature profile against radius and the gas density is relatively lower atthe optical outskirts. Thus it is found that X-ray bright and faint ellipticalgalaxies are clearly distinguished by the temperature and gas density profile.The mass profile is well scaled by a virial radius $r_{200}$ rather than anoptical-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 ofclusters 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 constantmass-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 thusrequires a presence of massive dark matter halo. From the deprojection analysiscombined with the {\it XMM-Newton} data, we found that X-ray dim galaxies, NGC3923, NGC 720, and IC 1459, also have a high $M/L_{\rm B}$ ratio of 20--30 at20 kpc, comparable to that of X-ray luminous galaxies. Therefore, dark matteris indicated to be common in elliptical galaxies, and their distribution almostfollows the NFW profile, as well as galaxy clusters.Comment: 33 pages, 11 figures, to appear in ApJ 636 No.2, ApJ 10 January 200