  We present HI observations of 54 galaxies in the Pegasus cluster. The
observations include single dish HI measurements, obtained with the Arecibo
telescope for all 54 galaxies in the sample, as well as HI images, obtained
with the VLA for 10 of these. The Arecibo profiles reveal an overall HI
deficiency in the cluster, with ~40% of the galaxies in the core of the cluster
showing modest deficiencies of typically a factor of 2-3. The HI morphology of
some galaxies shows that the HI disk is smaller than the optical disk and
slightly offset from the stars. We find a correlation between HI deficiency and
the ratio of the HI disk size to optical disk size. More HI deficient galaxies
have relatively smaller HI disks, a configuration that is usually attributed to
an interaction between the ISM of the galaxy and the hot ICM. Such a result is
surprising since the Pegasus cluster has a low level of X-ray emission, and a
low velocity dispersion. The low velocity dispersion, coupled with the lack of
a dense hot ICM indicate that ram pressure stripping should not play a
significant role in this environment. In addition, two of the galaxies, NGC7604
and NGC7648, are morphologically peculiar. Their peculiarities indicate
contradictory scenarios of what is triggering their unusual star formation.
Halpha imaging, along with long-slit spectroscopy of NGC7648 reveal
morphological features which point to a recent tidal interaction. On the other
hand, Halpha imaging,along with VLA HI mapping, of NGC7604 reveal morphological
features suggestive of a ram pressure event. Our data indicate that ISM-ICM
interactions may play a role in a wider variety of environments than suggested
by simple ram pressure arguments.
