Nuclear activity in radio active galactic nuclei (AGN) is thought to be connected with the presence and kinematic properties of the gas
in the circumnuclear regions. To understand the full picture of the interplay between gas and AGN, systematic studies of large AGN
samples are needed. Using the Westerbork Synthesis Radio Telescope, we carried out neutral hydrogen (HI) absorption observations of a
flux-selected (> 50 mJy at 1.4 GHz) sample of 101 radio AGN. We detect HI in 32 sources, making our collection the largest HI absorption
sample to date.
We explore the possibility of detecting gas in radio sources at low column density level using, for the first time, stacking of HI
absorption spectra. In this talk I will present the results of our stacking experiment.
Direct HI detections show a broad variety of widths, shapes, and kinematic properties, clearly an HI "Zoo". I will discuss the detection
rate and kinematics of HI absorption in young vs. evolved radio sources in relation to AGN feeding and feedback processes.
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