Radio continuum emission and Hi gas accretion in the NGC 5903/5898 compact group of early-type galaxies

Abstract

We discuss the nature of the multicomponent radio continuum and Hi emission associated with the nearby galaxy group comprised of two dominant ellipticals, NGC 5898 and NGC 5903, and a dwarf lenticular ESO 514-G003. Striking new details of radio emission are unveiled from the second Data Release of the ongoing TIFR GMRT Sky Survey (TGSS) which provides images with a resolution of ∼24 × 18arcsec2 and a typical rms noise of 5mJy at 150MHz. Previous radio observations of this compact triplet of galaxies include images at higher frequencies of the radio continuum as well as Hi emission, the latter showing huge Hi trails originating from the vicinity of NGC 5903 where Hi is in a kinematically disturbed state. The TGSS 150-MHz image has revealed a large asymmetric radio halo around NGC 5903 and also established that the dwarf S0 galaxy ESO 514-G003 is the host to a previously known bright double radio source. The radio emission from NGC 5903 is found to have a very steep radio spectrum (α∼-1.5) and to envelope a network of radio continuum filaments bearing a spatial relationship to the Hi trails. Another noteworthy aspect of this triplet of early-type galaxies highlighted by the present study is that both its radio-loud members, namely NGC 5903 and ESO 514-G003, are also the only galaxies that are seen to be connected to an Hi filament. This correlation is consistent with the premise that cold gas accretion is of prime importance for triggering powerful jet activity in the nuclei of early-type galaxies. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.