J1615+5452: a remnant radio galaxy in the ELAIS-N1 field

TL;DR

This paper reports the discovery and analysis of a remnant radio galaxy at z~0.33, characterized by diffuse emission, steep spectrum, and signs of an aging, dying AGN with no active core or jets.

Contribution

The study provides detailed spectral and morphological analysis of a newly identified remnant radio galaxy, highlighting its evolutionary stage and energy supply shortage.

Findings

Spectral indices between -1.5 and -0.61 indicating aged electron populations

Absence of core, jets, or hotspots at 1.4 GHz suggesting a dying phase

Estimated synchrotron age of approximately 76 million years

Abstract

We report the discovery of a remnant radio AGN J1615+5452 in the field of ELAIS-N1. GMRT continuum observations at 150, 325 and 610 MHz combined with archival data from the 1.4 GHz NVSS survey were used to derive the radio spectrum of the source. At a redshift $z \sim$ 0.33, J1615+5452 has a linear size of $\sim$ 100 kpc and spectral indices ranging between $\alpha^{1400}_{610} < -1.5$ and $\alpha^{325}_{150} = -0.61 \pm 0.12$. While the source has a diffuse radio emission at low frequencies, we do not find evidence of core, jets or hotspots in the 1.4\,GHz VLA data of $\sim 5$ arcsec angular resolution. Such morphological properties coupled with a curved radio spectrum suggest that the AGN fueling mechanisms undergo a shortage of energy supply which is typical of a dying radio AGN. This is consistent with the observed steep curvature in the spectrum $\Delta\alpha \approx -1$, the estimated synchrotron age of $t_{\rm s}=76.0^{+7.4}_{-8.7}$ Myr and a $t_{\rm off}/t_{\rm s}$ ratio of $\sim 0.3$.