2007AJ....133.1104L

We present neutral hydrogen observations of 54 galaxies in the Pegasus Cluster. The observations include single-dish H I measurements, obtained with the Arecibo telescope for all 54 galaxies in the sample, as well as H I images obtained with the Very Large Array (VLA) for 10 of these. The Arecibo profiles reveal an overall H I 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 H I morphology of some galaxies shows that the H I disk is smaller than the optical disk and slightly offset from the stars. We find a correlation between H I deficiency and the ratio of the H I disk size to optical disk size. More H I-deficient galaxies have relatively smaller H I disks, a configuration that is usually attributed to an interaction between the interstellar medium (ISM) of the galaxy and the hot intracluster medium (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, NGC 7604 and NGC 7648, are morphologically peculiar. Their peculiarities indicate contradictory scenarios of what is triggering their unusual star formation. Hα imaging, along with long-slit spectroscopy of NGC 7648, reveal morphological features that point to a recent tidal interaction. On the other hand, Hα imaging of NGC 7604 reveals a strong episode of star formation concentrated into an asymmetric arc, preferentially located on one side of the galaxy. VLA H I mapping shows that H I is also highly concentrated into that region, 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.