Detecting the cold neutral gas in young radio galaxies.

James Allison (University of Sydney)

HI absorption provides direct evidence of the presence of cold neutral gas in/out-flows, indicating that interaction between the Active Galactic Nucleus (AGN) with the interstellar medium is common. I will present an overview of results from our search for cold HI gas around compact radio sources using the Australia Telescope Compact Array (ATCA). Selected from the AT20GHz survey, these compact sources are thought to represent some of the most recently triggered radio-loud AGNs in the nearby Universe. Application of our novel detection technique to these ATCA data has proved robust in finding and modelling low S/N 21cm lines, and has revealed the presence of an unusually weak, broad absorption-line in an early-type galaxy.

I will also discuss a recent search for HI absorption in nearby radio galaxies using data from the HI Parkes All-sky Survey (HIPASS). Given the low optical depth sensitivity of HIPASS, the number of detected associated HI absorbers is very promising for early science with the Square Kilometer Array pathfinders, with which we will be able to study the HI content of the Universe to much higher redshifts.

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