Cusp-core dichotomy of elliptical galaxies: the role of thermal evaporation

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.