Letter to the Editor

Turbulent and fast motions of H₂ gas in active galactic nuclei

¹ Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot, Irfu/Service d’Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette, France
e-mail: kalliopi.dasyra@obspm.fr
² Observatoire de Paris, LERMA (CNRS:UMR 8112), 61 Av. de l’Observatoire, 75014 Paris, France

Received: 19 July 2011
Accepted: 13 August 2011

Abstract

Querying the Spitzer archive for optically-selected active galactic nuclei (AGN) observed in high-resolution-mode spectroscopy, we identified radio and/or interacting galaxies with highly turbulent motions of H₂ gas at a temperature of a few hundred Kelvin. Unlike all other AGN that have unresolved H₂ line profiles at a spectral resolution of  ~600, 3C 236, 3C 293, IRAS 09039+0503, MCG-2-58-22 and Mrk 463E have intrinsic velocity dispersions exceeding 200 km s^-1 for at least two of the rotational S0, S1, S2, and S3 lines. In a sixth source, 4C 12.50, a blue wing was detected in the S1 and S2 line profiles, indicating the presence of a warm molecular gas component moving at  − 640 km s^-1 with respect to the bulk of the gas at systemic velocity. Its mass is 5.2  ×  10⁷ M_⊙, accounting for more than one fourth of the H₂ gas at 374 K, but less than 1% of the cold H₂ gas computed from CO observations. Because no diffuse gas component of 4C 12.50 has been observed to date to be moving at more than 250 km s^-1 from systemic velocity, the H₂ line wings are unlikely to be tracing gas in shock regions along the tidal tails of this merging system. They can instead be tracing gas driven by a jet or entrained by a nuclear outflow, which is known to emerge from the west nucleus of 4C 12.50. It is improbable that such an outflow, with an estimated mass loss rate of 130 M_⊙ yr^-1, entirely quenches the star formation around this nucleus.