uGMRT detections of H i 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 ≈ 78 M ⊙ 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.

Compact steep-spectrum and peaked-spectrum radio sources

“…Besides re-detecting Hi absorption in 6 known systems, they surprisingly did not detect any new system in the spectra of 108 sources free from RFI, and none beyond a redshift of 0.7. In contrast, for a sample of 11 compact (mostly CSS/PS) sources in the intermediate redshift range 0.7 < z < 1, 4 were detected in Hi absorption using the uGMRT by Aditya (2019).…”

“…In this scenario, activity lasts ∼ 10 3 -10 4 yr and episodes are separated by ∼ 10 4 -10 6 yr (Czerny et al, 2009;Wu, 2009a;Siemiginowska et al, 2010). Jet disruption is another way of producing short-lived radio sources (e.g., De Young, 1991;Higgins et al, 1999;Wang et al, 2000;Wiita, 2004;Sutherland and Bicknell, 2007;Wagner and Bicknell, 2011;Mukherjee et al, 2016Mukherjee et al, , 2017Mukherjee et al, , 2018bBicknell et al, 2018;Aditya, 2019). If the jets in some sources disrupt (and the source fades quickly) before the radio source propagates out of the core, the distribution of number vs source size (O'Dea and ) can be reproduced (Alexander, 2000;Kaiser and Best, 2007;An and Baan, 2012).…”

The First Large Absorption Survey in Hi(FLASH): I. Science goals and survey design

“…While this has been well studied in the nearby Universe, it is crucial to extend these studies to higher redshifts when feedback processes have the most impact (Hopkins & Beacom 2006). Recent studies searching for neutral gas outflows at z ∼ 1 have also shown evidence for fast outflows, although the sample size is still relatively small (Aditya & Kanekar 2018a;Aditya 2019). While FLASH will not be sensitive to the low optical depths typically observed in fast outflows for the majority of sources, it will provide a sample of powerful radio galaxies with large gas reservoirs which can be targeted with deeper observations using, for example, MeerKAT.…”

FLASH pilot survey: detections of associated 21 cm H i absorption in GAMA galaxies at 0.42 &lt; z &lt; 1.00

“…In the redshift range 0.42 < 1.0 there are a few previous studies (e.g. Aditya & Kanekar 2018b;Aditya 2019;Murthy et al 2022), but we chose to us our own data to minimize any selection bias. As noted above, the detection rate here is 2.9 +9.7 −2.6 %.…”