Hi in Arp 72 and similarities with M51-type systems

Abstract

We present neutral hydrogen (Hi) 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 Hi tails and a bridge due to tidal interactions. Hi column densities ranging from 0.8-1.8 × 10 20atomscm -2 in the eastern tidal tail to 1.7-2 × 10 21atomscm -2 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 Hi features in Arp 72 as well as in other M-51 systems depicting similar optical and Hi features. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.