uGMRT search for cold gas at z~1-1.4 towards red quasars

TL;DR

This study used uGMRT to search for cold gas via HI 21-cm and OH 18-cm absorption in red quasars at z~1-1.4, finding some detections of HI absorption and discussing the relationship with MgII absorption and dust reddening.

Contribution

First detection of HI 21-cm absorption towards a z~1.1 quasar with analysis of its relation to MgII absorption and reddening effects.

Findings

HI 21-cm absorption detected towards J1521+5508 at systemic redshift.

Absence of HI 21-cm absorption at other MgII redshifts suggests clumpy gas distribution.

No OH absorption detected, setting upper limits on OH/H I ratio.

Abstract

We present results from our search for HI 21-cm and OH 18-cm absorption at z~1-1.4 towards red quasars showing strong MgII absorption using uGMRT. The quasars J1501+1822 and J1521+5508 show multiple strong associated MgII absorption at z~1.1 and signature of reddening in their optical spectra. We report the detection of HI 21-cm absorption towards J1521+5508 at the systemic redshift of the quasar, with N(HI) =(1.2 +/- 0.2) x 10^{20} cm^{-2} for spin temperature of 100 K and unit covering factor. The HI 21-cm absorption is offset from the blueshifted strong MgII absorbers by >~1500 km/s. We do not detect HI 21-cm absorption at the redshift of the associated MgII absorption and at the systemic redshift towards J1501+1822. We argue that lack of one-to-one correspondence between MgII and HI 21-cm absorption could be related with clumpiness of the neutral gas and the radio and optical sightlines probing different volume of the gas. We find that the presence of strong associated MgII absorption and reddening in the optical spectra of the quasars lead to an increased detection rate of associated HI 21-cm absorption at z>=1. We also report non-detection of intervening OH absorption ([OH]/[HI] <= (1-4) x 10^{-8}) at z = 1.3 towards two red quasars, J0850+5159 and J0852+3435, which show strong metal and HI 21-cm absorption and the 2175 A dust extinction bump.