Colloquium - Cold gas in the center of radio-loud galaxies: New perspectives on triggering and feedback from HI absorption surveys and molecular gas.

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Nuclear activity in radio galaxies (AGN) may be connected with the presence and kinematical properties of the surrounding interstellar medium. In this talk, I will present two projects that aim to link the properties of the neutral hydrogen (HI) and molecular gas in the centre of early-type galaxies to the triggering, fuelling and feedback effects of radio AGN.

The first project investigates the presence of HI absorption in a sample of radio AGN to link the properties of the lines to the evolutionary stage of the AGN as well as to the properties of its host galaxy. I will present a comprehensive statistics of HI outflows, albeit derived from shallow observations. I will also consider the sources where HI absorption is not detected to perform stacking experiments that allow us to probe the general properties of HI in radio AGN.

The second project is a multi-wavelength study of a young radio AGN (PKS B17181-649) to understand how cold gas may trigger the radio nuclear activity. We observed the HI, the molecular hydrogen and the carbon monoxide gas (CO). All these components indicate that cold gas is contributing to fuel the central nuclear activity. The kinematical properties of the CO detected in absorption strongly suggest that molecular clouds close to the AGN (r<100 pc) are accreting onto the central supermassive black hole.

To conclude, I will discuss on the implications of the results of these projects on the upcoming neutral hydrogen surveys from the SKA pathfinders and precursors.