The discovery of a long H I plume near the peculiar galaxy NGC 2782 (ARP 215)

The peculiar starburst galaxy NGC 2782 (Arp 215) is mapped in the 21-cm H I line using the VLA, and a massive H I plume extending about 5 arcmin toward the northwest is discovered which contains 1.4 x 10 to the 9th solar mass of atomic hydrogen (about 40 percent of the total H I mass of the system). There is also a shorter H I structure extending toward the east, which contains 6.6 x 10 to the 8th solar mass of H I. In the Arp Atlas photograph, NGC 2782 has a disturbed body with bright arcs, possibly ripples, throughout the disk, and a pronounced stellar tail extending 2.7 arcmin toward the east. The eastern H I structure is associated with the beginning of this stellar tail. PDS scanning of the Palomar plates in the vicinity of NGC 2782 reveals a low surface-brightness counterpart to the long HI plume in the northwest. The most likely formation scenario for NGC 2782 is a merger, possibly of unequal mass galaxies, where at least one of the galaxies is gas rich.