VLA Observations of Unusual H I Distributions for Coma Cluster Spirals

Abstract

The influence of the cluster environment on the neutral hydrogen contents of spiral galaxies in clusters has been well established over the past decade. It is found that spirals in the central regions of those clusters having the most intracluster gas and the lowest percentage of spirals exhibit H I deficiencies (when compared with field spirals of the same size and luminosity and morphological type) ranging from a factor of 2 to 10. The Virgo cluster is the best-studied example of the moderately deficient class, and the Coma cluster is the extreme case of the very deficient type. Until recently, however, it has not been possible to study the details of the distribution of the H I in these deficient cluster galaxies. The first detailed studies with synthesis telescopes were carried out (on the Virgo cluster) on the WSRT by Warmels (1986) and on the VLA by van Gorkom et al. (1984). These showed that the H I in the deficient spirals was primarily missing from the outer parts of the galaxies; that is, that the size of the H I disks was much smaller than the optical disks, the opposite of the usual situation in the field. Furthermore, van Gorkom et al. (1984) and Cayette et al. (1988) have several cases of very asymmetric H I distributions, which can reasonably be attributed to either tidal interactions with other cluster members, or to interactions (such as ram-pressure stripping) with the intracluster medium. With these interesting results in hand, I have observed the H I distributions in several deficient spirals in the Coma cluster, where one might expect even stronger effects. Here I give a preliminary account of these observations.

On leave from Department of Astronomy, University of Washington, Seattle, Washington, U.S.A.