Cooling flows and the entropy of the intragroup medium
  We study steady, homogeneous and subsonic cooling flows in poor clusters of galaxies in light of the recent proposal that radiative cooling of the intracluster gas can explain the observations of the `entropy floor' and other related X-ray observations. We study a family of cooling flow solutions parameterized by the mass flux rate, and then determine the resulting entropy and the X-ray luminosity. We find that cooling flows with mass flux rates in excess of 1000 M_{solar} per yr are required to explain the observations of entropy and X-ray luminosity. In view of the observed lack of such large flows in rich clusters, our calculations suggest that heating sources are needed, in addition to the effect of radiative cooling, to explain the observations. 
Biman B. Nath (Raman Research Institute, India)