A circumnuclear disk of atomic hydrogen in Centaurus A

Abstract

We present new observations, performed with the Australia Telescope Compact Array, of the H I absorption in the central regions of Centaurus A. For the first time, absorption is detected against the radio core at velocities blueshifted with respect to the systemic velocity. Moreover, the data show that the nuclear redshifted absorption component is broader than reported before. With these new results, the kinematics of the H I in the inner regions of Cen A appears very similar to that observed in emission for the molecular circumnuclear disk. This suggests that the central H I absorption is not, as was previously claimed, evidence of gas infall into the AGN, but instead is due to a cold, circumnuclear disk.