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30th of September 2019
An ASKAP survey for HI absorption towards dust-obscured quasars
by Glowacki et al.
Glowacki et al. present the results of a HI absorption line survey at towards 34 obscured quasars with the Australian SKA Pathfinder (ASKAP) commissioning array. They detect three HI absorption line systems, with one of these systems previously unknown. Through optical follow-up for two sources, they found that in all detections the HI gas is associated with the active galactic nuclei (rather than an intervening galaxy somewhere along the line of sight), and hence that these galactic nuclei are obscured by material within their host galaxies. Shallow and asymmetric HI absorption features are found, which agrees with previous findings that the cold neutral medium in compact radio galaxies is typically kinematically disturbed by the active galactic nucleus.

The image above shows the HI absorption detection made towards PKS 1829−718. The top panel shows the data following subtraction of the best-fitting continuum model (grey), and the best-fitting multiple Gaussian spectral-line model (black). The individual components are displayed in green. The red line in the bottom panel represents the residuals of the data after subtraction of this model fit. The spectrum is centred on the optical spectroscopic redshift obtained of z = 0.53, and one absorption feature (labeled 5) is aligned with this velocity. The other absorption features are redshifted up to ∼350 km/s, that is, moving away from the observer towards the nucleus. These redshifted components are probably gas clouds in-falling toward the AGN. 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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