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15th of June 2016
ATNF Colloquium
Neutral hydrogen properties in radio sources
by Filippo Maccagni (University of Groningen)
Abstract. AGN may play a crucial role in regulating the balance between accretion and ejection of gas in a galaxy. Yet, it is unclear how the energy released by the AGN couples with the surrounding ISM. Neutral hydrogen (HI) absorption in radio-AGN is a powerful tool to identify cold gas interacting with the radio source. In this scenario, ASKAP and Apertif plan to investigate the occurrence of HI absorption in radio-AGN with two surveys FLASH and SHARP. In preparation for these surveys, our research group observed 250 radio sources (S > 30 mJy; 0.02 < z < 0.25) with the WSRT, detecting HI in one AGN every four. In this talk, I will show the main results of this preliminary survey. In particular, we developed a software able to determine the most likely distribution of cold gas which reproduces the observed absorption line. We found that in most sources the absorbed HI is assembled in a galactic disk or in a small circum-nuclear disk, nevertheless not all profiles can be simply explained by a rotating disk. In some cases, the lines may also trace unsettled gas which may be outflowing from the radio source or falling into it. This seems to occur more often in compact and powerful, hence young, radio sources. In this talk, I will also focus on a case study we observed in high detail with the Compact Array, the newly born radio source (< 102 years) PKS 1718-649. Against its very compact (r < 2 pc) radio core we detected HI absorption with unsettled kinematics, and follow up observations with SINFONI show that the warm molecular hydrogen in the innermost 75 pc may have the same unsettled kinematics. I will show how these properties of the HI and H2 suggest the cold gas is fuelling this newly born radio source.

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