The prevalence of cooling flows in early-type galaxies

The density profiles of the hot interstellar gas in 18 galaxies, mostly ellipticals, have been determined using X-ray data from the Einstein Observatory. Radiative cooling is important throughout most of this gas leading to mass-deposition rates of between 0.02 and $$3M_\odot \text {yr}^{-1}$$. There are problems in determining the nature of the resultant cooling flows since these mass-deposition rates are significantly less than the expected injection of gas from stellar mass loss, and supernova heating is not accounted for. We suggest possible solutions involving a multi-phase medium and cooling outflows. Cooling flows in early-type galaxies have immediate implications for their chemical evolution, optical line emission, star formation, the behaviour of cold discs, the activity of the nucleus and the confinement of radio jets.