2018MNRAS.473...59A

We report the first detections of associated H I 21 cm absorption in Gigahertz-peaked-spectrum (GPS) sources at high redshifts, z > 1, using the Giant Metrewave Radio Telescope (GMRT). Our GMRT search for associated H I 21 cm absorption in a sample of 12 GPS sources yielded two new detections of absorption, towards TXS 1200+045 at z = 1.226 and TXS 1245-197 at z = 1.275, and five non-detections. These are only the sixth and seventh detections of associated H I 21 cm absorption in active galactic nuclei (AGNs) at z > 1. Both H I 21 cm absorption profiles are wide, with velocity spans between nulls of ≃600 km s^–1 (TXS 1200+045) and ≃1100 km s^–1 (TXS 1245-197). In both absorbers, the large velocity spread of the absorption and its blueshift from the AGN suggest that it arises in outflowing neutral gas, perhaps driven by the radio jets to high velocities. We derive mass outflow rates of {dot}M ~32   M_☉ yr^–1 (TXS 1200+045) and {dot}M ~18   M_☉ yr^–1 (TXS 1245-197), comparable to the mass outflow rates seen earlier in low-redshift AGNs.