The warm molecular hydrogen of PKS B1718-649: feeding a newly born radio AGN

TL;DR

This study uses VLT observations to analyze molecular hydrogen in PKS B1718-649, revealing a double disk structure and gas inflow that likely feeds the young radio AGN.

Contribution

It provides the first detailed kinematic analysis of H2 in PKS B1718-649, showing gas inflow towards the supermassive black hole in a young radio AGN.

Findings

Discovery of a double disk structure with different orientations.

Detection of redshifted H2 gas indicating inflow.

Unsettled HI clouds likely contributing to AGN fueling.

Abstract

We present new SINFONI VLT observations of molecular hydrogen (H2) in the central regions (< 2.5 kpc) of the youngest and closest radio source PKS B1718-649. We study the distribution of the H2 traced by the 1-0 S(1) ro-vibrational line, revealing a double disk structure with the kinematics of both disks characterised by rotation. An outer disk (r > 650 pc) is aligned with other components of the galaxy (atomic hydrogen, stars, dust), while the inner disk (r< 600 pc) is perpendicular to it and is polar with respect to the stellar distribution. However, in the innermost 75 pc, the data show the presence of H2 gas redshifted with respect to the rotating inner disk ($\Delta v\,$+150 km/s) which may trace gas falling into the super-massive black hole associated with the central radio source. Along the same line of sight, earlier observations had shown the presence in the central regions of PKS B1718-649 of clouds of atomic hydrogen with similar unsettled kinematics. The range of velocities and mass of these unsettled clouds of HI and H2 suggest they may be actively contributing in fuelling the central newly-born radio source.