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Obscuration of quasars by accreted gas and dust, or dusty intervening
galaxies, can cause active galactic nuclei (AGN) to be missed in
optically-selected surveys. Radio observations can overcome this dust
bias. In particular, radio observations of neutral hydrogen (HI) absorption provide
information on how the AGN can impact on the cold neutral gas medium
within the host galaxy, or the population of intervening galaxies,
through the observed line of sight gas kinematics. Glowacki et
al. have surveyed 34 radio-loud obscured quasars with the ASKAP
commissioning array to search for cold neutral gas along the line of
sight. Sources were selected to have flux densities greater than 1 Jy
at either 843 MHz or 1.4 GHz, and at 5 GHz. A sub-sample of optically
faint AGN was selected, and a sub-sample of quasars with red WISE
mid-infrared colours, as both are consistent with absorbing material
in (or in front of) the galaxy. A total
of 34 radio-bright sources were chosen. The image above shows the
WISE two-colour distribution of the sample. The coloured ellipses
indicate the typical colour properties seen for elliptical galaxies,
spiral galaxies and QSOs. The Carilli detections and non-detections
refer to a similar survey undertaken by Carilli et al.
More details are given in
the preprint of the paper,
to be published in
Monthly Notices of the Royal Astronomical Society.
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