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

TL;DR

This study uses new low-frequency radio observations to reveal complex radio and HI gas structures in the NGC 5903/5898 galaxy group, highlighting the role of cold gas accretion in galaxy activity.

Contribution

It provides the first detailed low-frequency radio imaging of the group, linking radio features with HI trails and suggesting cold gas accretion triggers nuclear activity.

Findings

Discovery of a large asymmetric radio halo around NGC 5903

Identification of a double radio source in ESO514-G003

Correlation between radio emission and HI filaments

Abstract

We discuss the nature of the multi-component 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 ESO514-G003. Striking new details of radio emission are unveiled from the 2nd Data Release of the ongoing TIFR.GMRT.SKY.SURVEY (TGSS) which provides images with a resolution of ~ 24 arcsec x 18 arcsec 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 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 SO galaxy ESO514-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 ({\alpha} ~ -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 ESO514-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.