Hot Atmospheres, Cold Gas, AGN Feedback and the Evolution of Early Type
  Galaxies: a Topical Perspective
  Most galaxies comparable to or larger than the mass of the Milky Way host
hot, X-ray emitting atmospheres, and many such galaxies are radio sources. Hot
atmospheres and radio jets and lobes are the ingredients of radio-mechanical
active galactic nucleus (AGN) feedback. While a consensus has emerged that such
feedback suppresses cooling of hot cluster atmospheres, less attention has been
paid to massive galaxies where similar mechanisms are at play. Observation
indicates that the atmospheres of elliptical and S0 galaxies were accreted
externally during the process of galaxy assembly and augmented significantly by
stellar mass loss. Their atmospheres have entropy and cooling time profiles
that are remarkably similar to those of central cluster galaxies. About half
display filamentary or disky nebulae of cool and cold gas, much of which has
likely cooled from the hot atmospheres. We review the observational and
theoretical perspectives on thermal instabilities in galactic atmospheres and
the evidence that AGN heating is able to roughly balance the atmospheric
cooling. Such heating and cooling may be regulating star formation in all
massive spheroids at late times.
