Study of giant radio galaxies using spectroscopic observations from the Himalayan Chandra Telescope

TL;DR

This study confirms eleven giant radio galaxies through spectroscopic observations, measuring their sizes, redshifts, and AGN properties, revealing rare large-scale structures and potential AGN-driven outflows.

Contribution

First spectroscopic confirmation of eleven candidate giant radio galaxies, providing precise size, redshift, and AGN activity data, and identifying rare large GRGs and potential outflows.

Findings

All eleven sources confirmed as giants with sizes 0.7-2.9 Mpc.

Two GRGs exceed 2 Mpc, a rare size.

Potential AGN jet-driven outflow observed in one GRG.

Abstract

We present the results of spectroscopic observations of host galaxies of eleven candidate giant radio galaxies (GRGs), powered by active galactic nuclei (AGNs), conducted with the 2-m Himalayan Chandra Telescope (HCT). The primary aim of these observations, performed with the Hanle Faint Object Spectrograph Camera (HFOSC), was to secure accurate spectroscopic redshifts, enabling precise calculations of their projected linear sizes. Based on these measurements, we confirm all eleven sources as giants, with linear sizes ranging from 0.7 to 2.9 Mpc, including ten GRGs and one giant radio quasar (GRQ). One of the GRGs shows evidence of a potential AGN jet-driven ionized outflow, extending up to $\sim$12 kpc, which, if confirmed, would represent a rarely observed feature. Two of the confirmed GRGs exceed 2 Mpc in size, which are relatively rare examples of GRG. The redshifts of the host galaxies span 0.09323 $\leq$ z $\leq$ 0.41134. Using the obtained spectroscopic data, we characterised their AGN states based on the optical emission line properties. To complement these observations, archival radio and optical survey data were utilised to characterise their large-scale radio morphology and estimate projected linear sizes, arm-length ratios, flux densities, luminosities, and core dominance factors. These results provide new insights into the properties of GRSs and form a critical foundation for further detailed studies of their environments, AGN activity, and evolution using future high-sensitivity optical and radio datasets.