Stellar kinematics of X-ray bright massive elliptical galaxies
  We discuss a simple and fast method for estimating masses of early-type
galaxies from optical data and compare the results with X-ray derived masses.
The optical method relies only on the most basic observables such as the
surface brightness $I(R)$ and the line-of-sight velocity dispersion
$\sigma_p(R)$ profiles and provides an anisotropy-independent estimate of the
galaxy circular speed $V_c$. The mass-anisotropy degeneracy is effectively
overcome by evaluating $V_c$ at a characteristic radius $R_{\rm sweet}$ defined
from {\it local} properties of observed profiles. The sweet radius $R_{\rm
sweet}$ is expected to lie close to $R_2$, where $I(R) \propto R^{-2}$, and not
far from the effective radius $R_{\rm eff}$. We apply the method to a sample of
five X-ray bright elliptical galaxies observed with the 6-m telescope BTA-6 in
Russia. We then compare the optical $V_c$-estimate with the X-ray derived
value, and discuss possible constraints on the non-thermal pressure in the hot
gas and configuration of stellar orbits. We find that the average ratio of the
optical $V_c$-estimate to the X-ray one is equal to $\approx 0.98$ with $11 \%$
scatter, i.e. there is no evidence for the large non-thermal pressure
contribution in the gas at $\sim R_{\rm sweet}$. From analysis of the Lick
indices H$\beta$, Mgb, Fe5270 and Fe5335, we calculate the mass of the stellar
component within the sweet radius. We conclude that a typical dark matter
fraction inside $R_{\rm sweet}$ in the sample galaxies is $\sim 60\%$ for the
Salpeter IMF and $\sim 75 \%$ for the Kroupa IMF.
