Active galactic nuclei winds as the origin of the H2 emission excess in nearby galaxies

In most galaxies, the fluxes of rotational H-2 lines strongly correlate with star formation diagnostics [such as polycyclic aromatic hydrocarbons (PAHs)], suggesting that H-2 emission from warm molecular gas is a minor by-product of star formation. We analyse the optical properties of a sample of 309 nearby galaxies derived from a parent sample of 2015 objects observed with the Spitzer Space Telescope. We find a correlation between the [OI]lambda 6300 emission-line flux and kinematics and the H-2 S(3) 9.665 mu m/PAH11.3 mu m. The [OI]lambda 6300 kinematics in active galactic nuclei (AGNs) cannot be explained only by gas motions due to the gravitational potential of their host galaxies, suggesting that AGN-driven outflows are important to the observed kinematics. While H-2 excess also correlates with the fluxes and kinematics of ionized gas (probed by [O III]), the correlation with [O I] is much stronger, suggesting that H-2 and [O I] emissions probe the same phase or tightly coupled phases of the wind. We conclude that the excess of H-2 emission seen in AGNs is produced by shocks due to AGN-driven outflows and in the same clouds that produce the [OI] emission. Our results provide an indirect detection of neutral and molecular winds and suggest a new way to select galaxies that likely host molecular outflows. Further ground- and space-based spatially resolved observations of different phases of the molecular gas (cold, warm, and hot) are necessary to test our new selection method.