Wide-field HI absorption surveys with the Square Kilometre Array precursors will have the unique capability of finding atomic gas in the largely unexplored epoch between the local Universe and z~1, where there is scant existing data from 21-cm and Lyman-alpha surveys. While HI absorption is a tracer of the reservoir of cold neutral gas in galaxies available for star formation, it can also be used to reveal the extreme kinematics associated with jet-driven neutral outflows in radio-loud active galactic nuclei. Using the six-antenna Boolardy Engineering Test Array of ASKAP, we have demonstrated that in a single frequency tuning we can detect HI absorption over a broad range of redshifts between z = 0.4 and 1.0. As part of our early science and commissioning program, we are now carrying out a search for absorption towards a sample of the brightest GPS and CSS sources in the southern sky. These intrinsically compact sources present us with an opportunity to study the circumnuclear region of recently re-started radio galaxies, in some cases showing direct evidence of mechanical feedback through jet-driven outflows. With the sensitivity of the full ASKAP array we will be able to study the kinematics of atomic gas in a few thousand radio galaxies, testing models of radio jet feedback well beyond the nearby Universe.
Figure caption: Comparison of the ASKAP-BETA spectrum (black) and GBT
Curran et al. 2011) towards quasar PKS B2252-089. The velocity
is given with reference to the optical spectroscopic redshift of z = 0.6064