Remnant radio galaxy candidates of small angular sizes

Abstract

Remnant radio galaxies (RRGs), characterized by the cessation of AGN activity, represent a short-lived last phase of radio galaxy's life-cycle. Hitherto, searches for RRGs, mainly based on the morphological criteria, have identified large angular size sources resulting into a bias towards the remnants of powerful FR-II radio galaxies. In this study we make the first attempt to perform a systematic search for RRGs of small angular sizes ($<$30${}^{\prime \prime }$) in the XMM-LSS field. By using spectral curvature criterion we discover 48 remnant candidates exhibiting strong spectral curvature $i.e.$; ${\alpha }_{150\mathrm{MHz}}^{325\mathrm{MHz}}$ - ${\alpha }_{325\mathrm{MHz}}^{1.4\mathrm{GHz}}$ $\ge$0.5. Spectral characteristics at higher frequency regime ($>$1.4 GHz) indicate that some of our remnant candidates can depict recurrent AGN activity with an active core. We place an upper limit on the remnant fraction ($f_{\mathrm{rem}}$) to be 3.9$\%$, which increases to 5.4$\%$ if flux cutoff limit of S${}_{150\mathrm{MHz}}$ $\ge$10 mJy is considered. Our study unveils, hitherto unexplored, a new population of small-size ($<$200 kpc) remnant candidates that are often found to reside in less dense environments and at higher redshifts ($z$) $>$1.0. We speculate that a relatively shorter active phase and/or low jet power can be plausible reasons for the small size of remnant candidates.

arXiv commentAccepted for publication in Galaxies. 19 pages, 7 figures, 3 tables

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• WEAVE First Light Observations: Origin and Dynamics of the Shock Front in Stephan's Quintet
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