H I spectral line mapping is a powerful diagnostic tool for investigating interacting and peculiar galaxies. In concert with numerical simulations, such observations provide insight into the transformation and formation of galaxies, the distribution of material in the halos of galaxies, the timing of interaction-induced starbursts, and the possible evolutionary products of mergers.
An important outstanding questions is whether many normal systems formed via mergers. While a merger origin for most galaxies is a generic result of hierarchical structure formation scenarios, there are continued claims that merger remnants will differ from normal ellipticals (Mihos & Hernquist 1994, van den Marel & Zurek, these proceedings). H I observations can help address this question by identify evolved remnants of gas-rich mergers via the amounts and structure of any remaining tidal H I. Once identified, the structure of these remnants should be compared to ellipticals. If they are indeed different, then this might mean that the Hubble Sequence evolves with redshift, such that the merger of present day spirals evolve into ellipticals with different characteristics than present day ellipticals, and conversely that present day ellipticals had progenitors which differed in some manner from present day disk galaxies.
With future cm wave facilities we should be able to address the cosmological aspect of this question. For instance, an expanded VLA (cooled low frequency receivers, greatly expanded correlator) will be able to detect H I out to redshifts ~ 1. We should be able to image the gas-rich tidal features out to redshifts of z ~ 0.5 (Figure 5). We will thus be able to constrain the number density of gas-rich mergers at these redshifts, which will tell us how large the population of gas-rich merger remnants should be at the present epoch.
I thank Jacqueline van Gorkom for useful discussions and a careful reading of this manuscript, Jim Higdon & Min Yun for providing figures for my talk, and the organizers for the opportunity to attend such an interesting meeting.