Studying the late evolution of a radio-loud AGN in a galaxy group with LOFAR

TL;DR

This study uses LOFAR and GMRT observations to analyze the late-stage evolution of a radio-loud AGN in a galaxy group, revealing complex spectral properties and potential remnant structures, advancing understanding of AGN feedback and cosmic ray fate.

Contribution

It presents the discovery and detailed spectral analysis of a large radio galaxy in a galaxy group, including the identification of a possible radio remnant, using LOFAR and GMRT data.

Findings

Radio galaxy spans 650 kpc with asymmetrical jets and lobes.

Spectral index steepens toward the core, indicating aging or activity cessation.

Detection of a potential radio remnant surrounding a close pair of AGN.

Abstract

Feedback by radio-loud active galactic nuclei (AGN) in galaxy groups is not fully understood. Open questions include the duty cycle of the AGN, the spatial extent of the radio lobes, the effect they have on the intragroup medium, and the fate of the cosmic rays. We present the discovery of a 650 kpc-radio galaxy embedded in steep diffuse emission at $z = 0.18793 \pm 5 \times 10^{-5}$ located at the center of the galaxy group MaxBCG J199.31832+51.72503 using an observation from the LOFAR Two-meter Sky Survey (LoTSS) at the central frequency of 144 MHz. Subsequently, we performed a GMRT observation at the central frequency of 607 MHz to study the spectral properties of the source. The observations reveal a radio galaxy with a total radio power $P_{\rm tot, 1.4} \sim 2.1 \times 10^{24}$ W Hz$^{-1}$, exhibiting two asymmetrical jets and lobes. The derived spectral index map shows a steepening toward the inner regions and a steep-spectrum core region. We model the integrated radio spectrum, providing two possible interpretations: the radio source is evolved but still active or it is just at the end of its active phase. Finally, in the same field of view we have discovered Mpc-sized emission surrounding a close pair of AGN located at a redshift $z = 0.0587 \pm 2 \times 10^{-4}$ (SDSS J131544.56+521213.2 and SDSS J131543.99+521055.7) which could be a radio remnant source.