James Allison (SIfA)

James Allison Colloquium -- Detecting HI absorption in nearby radio galaxies using HIPASS

Abstract

Absorption of 21cm wavelength radiation by atomic hydrogen (HI) equips
the observer with a powerful tool to map the line-of-sight kinematics
of neutral gas in galaxies towards background radio
sources. Observations of the 21cm absorption-line have revealed highly
broadened and doppler-shifted lines associated with radio-loud active
galactic nuclei (AGNs). Such studies have provided direct evidence of
the presence of neutral gas in-fall and out-flows, indicating that
interaction between the AGN with the interstellar medium is common.

Using a method based on Bayesian model comparison, developed for
future all-sky absorption surveys with the Square Kilometer Array
precursor telescopes, we have searched for cold HI gas in over 200
nearby radio galaxies in the first-generation HI Parkes All-sky Survey
(HIPASS). I will present results from this search and follow-up
observations with the Australia Telescope Compact Array (ATCA). I will
also discuss results from a program of targetted observations with the
ATCA to detect HI absorption in galaxies hosting compact radio sources
selected from the AT 20GHz radio survey. Such observations enable us
to study the kinematics of neutral gas associated with potentially
young and newly triggered radio AGN.