The warm molecular hydrogen of PKS B1718–649

Feeding a newly born radio AGN

¹ Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
e-mail: maccagni@astro.rug.nl
² ASTRON, Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
³ Leiden Observatory, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands
⁴ Centro de Astrobiología (INTA-CSIC), Ctra de Torrejón a Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, Spain

Received: 20 December 2015
Accepted: 28 January 2016

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 (Δv ~ + 150 km s^-1), 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 H i and H₂ suggest they may be actively contributing to fuelling the central newly born radio source.