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26th of September 2019
An ASKAP survey for HI absorption towards dust-obscured quasars
by Glowacki et al.
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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