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

¹ Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Krakow, Poland
² Doctoral School of Exact and Natural Sciences, Jagiellonian University, Krakow, Poland
³ Astrophysics Division, National Centre for Nuclear Research, Pasteura 7, 02-093 Warsaw, Poland
⁴ WMO Arts & Science college, Muttil, Wayanad, Kerala 673122, India
⁵ Indian Institute of Astrophysics, Koramangala II Block, Bangalore 560 034, India

^⋆⋆ Corresponding authors; sagar.sethi@doctoral.uj.edu.pl; pratik.dabhade@ncbj.gov.pl

Received: 22 January 2025
Accepted: 6 February 2025

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 ionised outflow, extending up to ∼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 GRGs. The redshifts of the host galaxies span 0.09323 ≤ z ≤ 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 GRGs and form a critical foundation for further detailed studies of their environments, AGN activity, and evolution using future high-sensitivity optical and radio datasets.