We investigated the dynamical structure of 53 elliptical galaxies , based on the 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 _ { B } = 3 - 10 ( M _ { \odot } / L _ { \odot } ) . M / L _ { B } ratio of X-ray bright galaxies rises up steeply beyond 0.01 r _ { 200 } , and thus requires a presence of massive dark matter halo .
From the deprojection analysis combined with the XMM-Newton data , we found that X-ray dim galaxies , NGC 3923 , NGC 720 , and IC 1459 , also have a high M / L _ { 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 .