  We present a study of the relationship between the deficiency of neutral
hydrogen and the local three-dimensional number density of spiral galaxies in
the Arecibo catalog of global HI measurements (Springob et al. 2005). We find
that the dependence on density of the HI content is weak at low densities, but
increases sharply at high densities where interactions between galaxies and the
intra-cluster medium become important. This behavior is reminiscent of the
morphology-density relation (Dressler 1980) in that the effect manifests itself
only at cluster-type densities, and indeed when we plot both the HI
deficiency-density and morphology-density relations, we see that the densities
at which they "turn up" are similar. This suggests that the physical mechanisms
responsible for the increase in early types in clusters are also responsible
for the decrease in HI content.

Astrophysics