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




We discuss the nature of the multicomponent radio continuum and H i 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 × 18 arcsec2 and a typical rms noise of 5 mJy at 150 MHz. Previous radio observations of this compact triplet of galaxies include images at higher frequencies of the radio continuum as well as H i emission, the latter showing huge H i trails originating from the vicinity of NGC 5903 where H i 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 H i 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 H i 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.