H I deficiency in cluster spiral galaxies: dependence on galaxy size

Abstract

From the available H I data on spiral galaxies in three rich Abell clusters and the Virgo Cluster, it is shown that galaxies with medium to large optical sizes tend to be more severely deficient in atomic hydrogen than the small galaxies. This is so both in terms of the fractional number of galaxies that are deficient and the amount of gas lost by a galaxy. The fraction of H l-deficient galaxies increases with size over most of the size range, saturating or dropping only for the largest galaxies. We make a comparative study of various currently accepted gas removal mechanisms, namely those which are a result of galaxy-intracluster medium interactions, e.g., ram pressure stripping, as well as those due to galaxy-galaxy interactions, i.e., collisions and tidal interactions. We show that with the exception of tidal interactions, all of these mechanisms would produce a size dependence in H I deficiency that is the opposite of that observed. That is, the gas in the largest galaxies would be the least affected by these mechanisms. However, if there is significant mass segregation, these processes may give the trends observed in the size dependence of H I deficiency. We propose that tidal encounters between galaxies in subclumps or groups, which then merged to form clusters or were subsequently accreted by them, could have led to significant gas removal from these galaxies at early epochs. This could qualitatively explain the dependence of H I deficiency on galaxy size. Since all the gas removal mechanisms known are less effective on the galaxies of the largest sizes, the drop in the fraction of deficient galaxies for these sizes is accounted for.