Dynamic S0 Galaxies II: the Role of Diffuse Hot Gas
  Gas loss is thought to be important in SF quenching and morphological
transition during the evolution of S0 galaxies. In high density environments,
gas loss can be achieved via many external mechanisms. However, in relatively
isolated environments, where these external mechanisms cannot be efficient, gas
loss must be dominated by some internal processes. We perform Chandra analysis
of hot gas in five nearby isolated S0 galaxies, based on quantitative
subtraction of various stellar contributions. We find that all the galaxies
studied in the present work are X-ray faint, with the hot gas luminosity LX<5%
of the expected Ia SN energy injection rate. We further compare our results
with those from relevant recent papers, in order to investigate the energy
budget, cold-hot gas relation, and gas removal from S0 galaxies in isolated
environments. We find that elliptical and S0 galaxies are not significantly
different in LX at the low mass end (typically with LK<1e11Lsun). However, at
the high mass end, S0 galaxies tend to have significantly lower LX than
elliptical galaxies of the same stellar masses. We further discuss the
potential relation of the diffuse X-ray emission with the cold gas content in
S0 and elliptical galaxies. We find that LX/LK^2 tends to correlate positively
with the total cold gas mass M(H2+HI) for gas-poor galaxies with
M(H2+HI)<1e8Msun, while they anti-correlate with each other for gas-rich ones.
This cold-hot gas relation can be explained in a scenario of galaxy evolution,
with the leftover cold gas from the precursor star forming galaxy mainly
removed by the long-lasting Ia SN feedback. The two different trends for
gas-rich and -poor galaxies may be the results of the initial fast decreasing
SN rate and the later fast decreasing mass-loading to hot gas, respectively.
