Strong Molecular Hydrogen Emission and Kinematics of the Multiphase Gas in Radio Galaxies with Fast Jet-driven Outflows

Observations of ionized and neutral gas outflows in radio galaxies (RGs) suggest that active galactic nucleus (AGN) radio jet feedback has a galaxy-scale impact on the host interstellar medium, but it is still unclear how the molecular gas is affected. Thus, it is crucial to determine the physical conditions of the molecular gas in powerful RGs to understand how radio sources may regulate the star formation in their host galaxies. We present deep Spitzer Infrared Spectrograph (IRS) high-resolution spectroscopy of eight nearby RGs that show fast H I outflows. Strikingly, all of these H I-outflow RGs have bright H₂ mid-IR lines that cannot be accounted for by UV or X-ray heating. This strongly suggests that the radio jet, which drives the H I outflow, is also responsible for the shock excitation of the warm H₂ gas. In addition, the warm H₂ gas does not share the kinematics of the ionized/neutral gas. The mid-IR-ionized gas lines (with FWHM up to 1250 km s^-1 for [Ne II] 12.8 μm) are systematically broader than the H₂ lines, which are resolved by the IRS in ≈60% of the detected lines (with FWHM up to 900 km s^-1). In five sources, 3C 236, 3C 293, 3C 459, 4C 12.50, and PKS 1549-79, the [Ne II] 12.8 μm line, and to a lesser extent the [Ne III] 15.5 μm and [Ne V] 14.3 μm lines, clearly exhibits blueshifted wings (up to -900 km s^-1 with respect to the systemic velocity) that match well the kinematics of the outflowing H I or ionized gas. The H₂ lines do not show these broad wings, except tentative detections in 4C 12.50, 3C 459, and PKS 1549-79. This shows that, contrary to the H I gas, the H₂ gas is inefficiently coupled to the AGN jet-driven outflow of ionized gas. While the dissipation of a small fraction (<10%) of the jet kinetic power can explain the turbulent heating of the molecular gas, our data show that the bulk of the warm molecular gas is not expelled from these galaxies.