Remnant radio galaxy candidates of small angular sizes

Abstract

Remnant radio galaxies (RRGs), characterized by the cessation of AGN activity, representa short-lived last phase of radio galaxy’s life-cycle. Hitherto, searches for RRGs, mainly based onthe morphological criteria, have identified large angular size sources resulting into a bias towardsthe remnants of powerful FR-II radio galaxies. In this study we make the first attempt to performa systematic search for RRGs of small angular sizes (<30′′) in the XMM−LSS field. By usingspectral curvature criterion we discover 48 remnant candidates exhibiting strong spectral curvaturei.e.,α325 MHz150 MHz−α1.4 GHz325 MHz≥0.5. Spectral characteristics at higher frequency regime (>1.4 GHz)indicate that some of our remnant candidates can depict recurrent AGN activity with an activecore. We place an upper limit on the remnant fraction (frem) to be 3.9%, which increases to 5.4% ifflux cutoff limit of S150 MHz≥10 mJy is considered. Our study unveils, hitherto unexplored, a newpopulation of small-size (<200 kpc) remnant candidates that are often found to reside in less denseenvironments and at higher redshifts (z)>1.0. We speculate that a relatively shorter active phaseand/or low jet power can be plausible reasons for the small size of remnant candidates.