Testing a simple recipe for estimating galaxy masses from minimal
  observational data
  The accuracy and robustness of a simple method to estimate the total mass
profile of a galaxy is tested using a sample of 65 cosmological
zoom-simulations of individual galaxies. The method only requires information
on the optical surface brightness and the projected velocity dispersion
profiles and therefore can be applied even in case of poor observational data.
In the simulated sample massive galaxies ($\sigma \simeq 200-400$ $\kms$) at
redshift $z=0$ have almost isothermal rotation curves for broad range of radii
(RMS $\simeq 5%$ for the circular speed deviations from a constant value over
$0.5R_{\rm eff} < r < 3R_{\rm eff}$). For such galaxies the method recovers the
unbiased value of the circular speed. The sample averaged deviation from the
true circular speed is less than $\sim 1%$ with the scatter of $\simeq 5-8%$
(RMS) up to $R \simeq 5R_{\rm eff}$. Circular speed estimates of massive
non-rotating simulated galaxies at higher redshifts ($z=1$ and $z=2$) are also
almost unbiased and with the same scatter. For the least massive galaxies in
the sample ($\sigma < 150$ $\kms$) at $z=0$ the RMS deviation is $\simeq 7-9%$
and the mean deviation is biased low by about $1-2%$. We also derive the
circular velocity profile from the hydrostatic equilibrium (HE) equation for
hot gas in the simulated galaxies. The accuracy of this estimate is about RMS
$\simeq 4-5%$ for massive objects ($M > 6.5\times 10^{12} M_\odot$) and the HE
estimate is biased low by $\simeq 3-4%$, which can be traced to the presence of
gas motions. This implies that the simple mass estimate can be used to
determine the mass of observed massive elliptical galaxies to an accuracy of
$5-8 %$ and can be very useful for galaxy surveys.
