2023/11/01 by Deka, P. P., Gupta, N., Chen, H. W. +14
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2311.00336
We report a new, rare detection of HI 21-cm absorption associated with a quasar (only six known at 15 GHz). The simplest explanation would be that no large HI column (N(HI)>1017 cm-2) is present towards the radio `core' and the optical AGN. Based on the joint optical and radio analysis of a heterogeneous sample of 16 quasars (zmedian = 0.7) and 15 radio galaxies (zmedian = 0.3) with HI 21-cm absorption detection and matched in 1.4 GHz luminosity (L\rm 1.4 GHz), a consistent picture emerges where quasars are primarily tracing the gas in the inner circumnuclear disk and cocoon created by the jet-ISM interaction. These exhibit L1.4 \rm GHz - ΔV\rm null correlation, and frequent mismatch between the radio and optical spectral lines. The radio galaxies show no such correlation and likely trace the gas from the cocoon and the galaxy-wide ISM outside the photoionization cone. The analysis presented here demonstrates the potential of radio spectroscopic observations to reveal the origin of the absorbing gas associated with AGN that may be missed in optical observations.