uGMRT detections of HI 21-cm absorption associated with intermediate redshift galaxies

Abstract

I report detections of four new HI 21-cm absorbers associated with sources at intermediate redshifts, 0.7 < z < 1.0. The sources are part of a sample of 11 radio-loud galaxies, all at 0.7 < z < 1.0, that were searched for associated HI 21-cm absorption using uGMRT. Previously, just four such absorbers were known in the literature at these redshifts; the current observations have increased the total to eight. The results indicate that the detection fraction at intermediate redshifts could be as high as that at lower redshifts, 30\%, on contrary to a much lower detection fraction observed in samples at z > 1. Three detections show strong blueshifted features, indicating cold gas outflows. These three sources also tentatively show excess [O II] line luminosity compared to a bulk of the remaining sample, possibly suggesting that the hosts of these AGNs harbour different environments, either due to interaction with the radio jets or due to excess star formation in the host galaxy. Further, a cold HI mass outflow rate of \approx 78 M_{sun} yr^{-1} , assuming T_s = 1000 K, is estimated for the detection towards SDSS J014652.79-015721.2, at z = 0.95904, which is the highest till date in comparison to similar estimates available in the literature.