2012MNRAS.420....2S

We present neutral hydrogen (H I) observations with the Giant Metrewave Radio Telescope (GMRT) of the interacting galaxies NGC 5996 and 5994, which make up the Arp 72 system. Arp 72 is an M51-type system and shows a complex distribution of H I tails and a bridge due to tidal interactions. H I column densities ranging from 0.8-1.8 {x} 10²⁰ atoms/cm2 in the eastern tidal tail to 1.7-2 {x} 10²¹ atoms/cm2 in the bridge connecting the two galaxies are seen to be associated with star-forming regions. We discuss the morphological and kinematic similarities of Arp 72 with M51, the archetypal example of the M51-type systems, and Arp 86, another M51-type system studied with the GMRT, and suggest that a multiple passage model of Salo & Laurikainen may be preferred over the classical single passage model of Toomre & Toomre to reproduce the H I features in Arp 72 as well as in other M-51 systems depicting similar optical and H I features. A cluster of outflows in the Vulpecula Rift