Contribution
Emission and absorption of circumnuclear molecular gas in Centaurus A
Presenter: Frank Israel (Sterrewacht Leiden)
Abstract: The nearest AGN Centaurus A is so close that its structures can be studied in detail. Its nucleus is a strong continuum source at millimeter wavelengths, and is surrounded by dense molecular gas precisely in the line-of-sight towards it. Nuclear spectroscopy at millimeter and submillimeter wavelengths reveals many molecular species in absorption and emission. The absorption spectra show a large number of velocity components, some distinct and very narrow, others blended together into a veritable forest of lines. There are strong absorption lines near the systemic velocity, flanked by weak blueshifted absorption and much stronger redshifted absorption covering a much larger velocity range. The unique combination of widely spread-out molecular line emission and absorption rather complicates interpretation of the spectra but also holds great promise for a determination of the physical properties of molecular gas very close to a supermassive black hole in an active galaxy nucleus.