Gravitational potential and X-ray luminosities of early-type galaxies
  observed with XMM-Newton and Chandra
  We study dark matter content in early-type galaxies and investigate whether
X-ray luminosities of early-type galaxies are determined by the surrounding
gravitational potential. We derived gravitational mass profiles of 22
early-type galaxies observed with XMM-Newton and Chandra. Sixteen galaxies show
constant or decreasing radial temperature profiles, and their X-ray
luminosities are consistent with kinematical energy input from stellar mass
loss. The temperature profiles of the other 6 galaxies increase with radius,
and their X-ray luminosities are significantly higher. The integrated
mass-to-light ratio of each galaxy is constant at that of stars within 0.5-1
r_e, and increases with radius, where r_e is the effective radius of a galaxy.
The scatter of the central mass-to-light ratio of galaxies was less in K-band
light. At 3r_e, the integrated mass-to-light ratios of galaxies with flat or
decreasing temperature profiles are twice the value at 0.5r_e, where the
stellar mass dominates, and at 6r_e, these increase to three times the value at
0.5r_e. This feature should reflect common dark and stellar mass distributions
in early-type galaxies: Within 3r_e, the mass of dark matter is similar to the
stellar mass, while within 6r_e, the former is larger than the latter by a
factor of two. By contrast, X-ray luminous galaxies have higher gravitational
mass in the outer regions than X-ray faint galaxies. We describe these X-ray
luminous galaxies as the central objects of large potential structures; the
presence or absence of this potential is the main source of the large scatter
in the X-ray luminosity.
