Quantified HI Morphology V: HI Disks in the Virgo Cluster
  We explore the quantified morphology of atomic hydrogen (HI) disks in the
Virgo cluster. These galaxies display a wealth of phenomena in their Hi
morphology, e.g., tails, truncation and warps. These morphological disturbances
are related to the ram-pressure stripping and tidal interaction that galaxies
undergo in this dense cluster environment. To quantify the morphological
transformation of the HI disks, we compute the morphological parameters of CAS,
Gini, and M20 and our own GM for 51 galaxies in 48 HI column density maps from
the VIVA project. Some morphological phenomena can be identified in this space
of relatively low resolution HI data. Truncation of the HI disk can be cleanly
identified via the Concentration parameter (C<1) and Concentration can also be
used to identify HI deficient disks (1<C<5). Tidal interaction is typically
identified using combinations of these morphological parameters, applied to
(optical) images of galaxies. We find that some selection criteria (Gini-M20,
Asymmetry, and a modified Concentration-M20) are still applicable for the
coarse (~15" FWHM) VIVA HI data. The phenomena of tidal tails can be reasonably
well identified using the Gini-M20 criterion (60% of galaxies with tails
identified but with as many contaminants). Ram-pressure does move HI disks into
and out of most of our interaction criteria: the ram-pressure sequence
identified by Vollmer et al. (2009) tracks into and out of some of these
criteria (Asymmetry based and the Gini-M20 selections, but not the
Concentration-M20 or the GM based ones). Therefore, future searches for
interaction using HI morphologies should take ram-pressure into account as a
mechanism to disturb HI disks enough to make them appear as gravitationally
interacting. One mechanism would be to remove all the HI deficient (C<5) disks
from the sample, as these have undergone more than one HI removal mechanism.
