Associated H{\sc i} absorption towards the core of the radio galaxy 3C 321

TL;DR

This study uses GMRT and VLA observations to analyze H I absorption and radio features in galaxy 3C 321, revealing complex gas dynamics, a potential relic plume, and active jets with recent spectral aging.

Contribution

First detailed H I absorption profile analysis towards 3C 321's core, revealing multiple components and gas kinematics, along with insights into the source's radio emission history.

Findings

H I absorption profile has three components, with two red-shifted features.

Neutral hydrogen column density estimated at 9.23×10^{21} cm^{-2}.

Detected a steep-spectrum plume possibly representing relic emission.

Abstract

We report the results of Giant Metrewave Radio Telescope (GMRT) observations of H{\sc i} absorption towards the FRII radio galaxy 3C321 (J1531+2404), which is associated with an active galaxy interacting with a companion. The absorption profile towards the radio core is well resolved and consists three components, of which the two prominent ones are red-shifted by 186 and 235 km s$^{-1}$ relative to the optical systemic velocity. The neutral hydrogen column density towards the core is estimated to be $N$(H{\sci})=9.23$\times10^{21}$(${T}_{\rm s}$/100)($f_{c}$/1.0) cm$^{-2}$, where ${T}_{\rm s}$ and $f_c$ are the spin temperature and covering factor of the background source respectively. We also present radio continuum observations of the source with both the GMRT and the Very Large Array (VLA) in order to understand the properties of a plume of emission at an angle of $\sim30^\circ$ to the source axis. This feature appears to have a steep high-frequency spectrum. The current hotspots and jet are active and seen in X-ray emission. The spectral ages of the lobes are $\lapp$26 Myr. We discuss the possibility that the plume could be relic emission due to an earlier cycle of activity.