Cool gas accretion, thermal evaporation and quenching of star formation
  in elliptical galaxies
  The most evident features of colour-magnitude diagrams of galaxies are the
red sequence of quiescent galaxies, extending up to the brightest elliptical
galaxies, and the blue cloud of star-forming galaxies, which is truncated at a
luminosity L~L*. The truncation of the blue cloud indicates that in the most
massive systems star formation must be quenched. For this to happen the
virial-temperature galactic gas must be kept hot and any accreted cold gas must
be heated. The elimination of accreted cold gas can be due to thermal
evaporation by the hot interstellar medium, which in turn is prevented from
cooling by feedback from active galactic nuclei.
