Active galactic nuclei winds as the origin of the H$_2$ emission excess
  in nearby galaxies
  In most galaxies, the fluxes of rotational H2 lines strongly correlate with
star formation diagnostics (such as polycyclic aromatic hydrocarbons, PAH),
suggesting that H2 emission from warm molecular gas is a minor byproduct of
star formation. We analyse the optical properties of a sample of 309 nearby
galaxies derived from a parent sample of 2,015 objects observed with the
Spitzer Space Telescope. We find a correlation between the [OI]6300
emission-line flux and kinematics and the H2 S(3)9.665um/PAH11.3um. The
[OI]6300 kinematics in Active Galactic Nuclei (AGN) can not 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 H2 excess also correlates with the fluxes and kinematics of ionized gas
(probed by [OIII]), the correlation with [OI] is much stronger, suggesting that
H2 and [OI] emission probe the same phase or tightly coupled phases of the
wind. We conclude that the excess of H2 emission seen in AGN 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.
