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Paper: HI in AGN
Volume: 106, The Minnesota Lectures on Extragalactic Neutral Hydrogen
Page: 268
Authors: Brinks, Elias; Mundell, Carole G.
Abstract: Neutral hydrogen exists on a wide range of scales in galaxies, from the outer--most regions, where it may be affected by tidal interactions, down to the central regions, where it may play a role in the fuelling of Active Galactic Nuclei (or AGN ) and where in turn it may be affected by the nuclear activity. Neutral hydrogen is an important tracer of galactic dynamics so observations of the detailed structure and kinematics of HI are vital for a study of the relationship between AGN and their host galaxies. As Seyfert galaxies are often gas--rich and are comparatively close, it is possible to conduct detailed HI {\em emission}--line studies to obtain information on the neutral gas distribution and kinematics, down to scales of a few hundred parsecs in the galaxy. High resolution HI {\em absorption}--line studies allow us to probe down to scales of a few tens of parsecs in nearby Seyfert galaxies and may give unambiguous detections of infall or outflow from the active nucleus. Studies of neutral hydrogen on large and small scales clearly offer a valuable opportunity to determine the link between the nuclear properties and the host galaxy environment. In this article we describe studies of HI in AGN with particular emphasis on Seyfert galaxies. We show that with sensitive high--resolution $\lambda$21--cm HI studies, emission on sub--kiloparsec scales may be mapped, revealing hitherto unprecedented detail in structure and kinematics. Absorption measurements have been used to probe structure on even finer scales ($\sim$10 pc in nearby Seyferts). In particular, detailed studies of the famous Seyfert galaxies NGC~1068 and NGC~4151 are presented whereas lower resolution studies of NGC~3227, NGC~4015 and NGC~6814 are reviewed.
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