Hot Gas Halos in Early-Type Field Galaxies
  We use Chandra and XMM-Newton to study the hot gas content in a sample of
field early-type galaxies. We find that the L_X-L_K relationship is steeper for
field galaxies than for comparable galaxies in groups and clusters. The low hot
gas content of field galaxies with L_K < L_star suggests that internal
processes such as supernovae driven winds or AGN feedback expel hot gas from
low mass galaxies. Such mechanisms may be less effective in groups and clusters
where the presence of an intragroup or intracluster medium can confine
outflowing material. In addition, galaxies in groups and clusters may be able
to accrete gas from the ambient medium. While there is a population of L_K <
L_star galaxies in groups and clusters that retain hot gas halos, some galaxies
in these rich environments, including brighter galaxies, are largely devoid of
hot gas. In these cases, the hot gas halos have likely been removed via ram
pressure stripping. This suggests a very complex interplay between the
intragroup/intracluster medium and hot gas halos of galaxies in rich
environments with the ambient medium helping to confine or even enhance the
halos in some cases and acting to remove gas in others. In contrast, the hot
gas content of more isolated galaxies is largely a function of the mass of the
galaxy, with more massive galaxies able to maintain their halos, while in lower
mass systems the hot gas escapes in outflowing winds.
