  There are two families of luminous elliptical galaxies: cusp galaxies, with
steep central surface-brightness profiles, and core galaxies, whose
surface-brightness profiles have flat central cores. Thermal evaporation of
accreted cold gas by the hot interstellar medium may be at the origin of this
cusp-core dichotomy: in less massive (hot-gas poor) galaxies central cores are
likely to be refilled by central starbursts following cold gas infall, while in
more massive (hot-gas rich) galaxies most cold gas is eliminated and central
cores survive. This scenario is consistent with the observation that cusp and
core galaxies differ systematically in terms of optical luminosity, X-ray gas
content, age of the central stellar population, and properties of the active
galactic nucleus.
