typeset using LATEX style emulateapjH I , H II , AND R - BAND OBSERVATIONS OF A GALACTIC MERGER

We present high-quality aperture synthesis observations of the neutral hydrogen distribution in a sample of ve galactic systems believed to be involved in progressive stages of merging: Arp 295, NGC 4676, NGC 520, NGC 3921, and NGC 7252. This is the rst time that the atomic hydrogen in such a broad range of disk mergers has been imaged. These data are supplemented by wide-eld images taken through a narrow band H lter, and by deep (R > 26.5 mag arcsec ?2) R-band surface photometry. We identify several trends along the merging sequence. In the early stages, large amounts of H i still exist within the galactic disks and star formation is widespread. The ionized gas emission often takes on the appearance of plumes and arcs emanating from the nuclear regions, which are presumably the sites of interaction-induced starbursts. In the nal stages there is little if any H i within the remnant bodies, and tidal material is seen moving inward. We conclude that as the merger rearranges the light prooles of the progenitor disk galaxies into r 1=4 prooles, it leads to an eecient conversion of the atomic gas into other forms within the main bodies of the merger remnants. This suggests that these remnants will evolve into elliptical galaxies in their atomic gas contents as well as their photometric properties. However the observations of NGC 520 reveal an extensive rotating gaseous disk, suggesting that perhaps some mergers will not destroy the atomic gas disks of the progenitors. The morphological similarity between the gaseous and stellar tails and the smooth gas kinematics connrm that gravity plays the dominant role in producing them. There are, however, some striking diierences between the faint gas and light distributions. H i mapping often reveals gaseous extension not at all apparent optically, and tidal features of diierent optical morphologies have diierent gas characteristics: the edge-brightened tails are gas-rich, while the featureless plumes and halos are gas-poor. Some of these features may be explained by the diierent velocity dispersions of the gas and stars, some by diierent gas contents in the progenitors, and some remain unexplained. Overall, large quantities of both gas and starlight L) are seen at large radii (r >50 h ?1 kpc). Since this material evolves on very long time scales, it may leave observable signatures for many Gyr.