Recurrent radio emission and gas supply: the case of the radio galaxy B2 0258+35

TL;DR

This paper reports the discovery of a faint, diffuse radio structure around the young CSS radio galaxy B2 0258+35, suggesting recurrent AGN activity fueled by gas cooling from the hot halo, with implications for galaxy evolution.

Contribution

It presents the first detailed analysis of a large-scale relic radio structure around B2 0258+35 and explores gas accretion mechanisms, including cooling from the hot halo, as triggers for recurrent AGN activity.

Findings

Discovery of a faint, diffuse radio structure around B2 0258+35.

Estimated age and accretion rate consistent with recurrent activity.

Implication that similar structures may be common around early-type galaxies.

Abstract

Outlined is the discovery of a very faint, diffuse, low surface-brightness (0.5 \mJybeam, 1.4 \mJyarcminsq on average) structure around the radio source B2 0258+35 hosted by an HI-rich early-type galaxy (NGC 1167). Since B2 0258+35 is a young Compact Steep Spectrum (CSS) source, the newly discovered structure could represent a remnant from an earlier stage of AGN activity. We go on by explaining in detail all the possibilities for triggering the radio activity in B2 0258+35 regarding gas accretion in a recurrent AGN activity framework. NGC 1167 hosts a very regular, extended and massive \HI\ disc that has been studied in great detail. Previous studies of the \HI\ closer to the core seem to go against the assumption of a circum-nuclear disc of \HI\ as the source of the accreting gas. We consider the cooling of gas from the hot, X-ray halo as a possible alternative option for the fueling of the AGN, as suggested in the case of other sources of similar radio power as B2 0258+35. Estimates are given for the age of the faint diffuse emission as well as for the current accretion rate, which are in good agreement with literature values. If our assumptions about the accretion mechanism are correct, similar large-scale, relic-like structures should be more commonly found around early-type galaxies and this will be hopefully confirmed by the next generation of sensitive, low-frequency radio surveys.