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

Abstract

Observations of ionized and neutral gas outflows in radio-galaxies (RG) suggest that AGN radio jet feedback has a galaxy-scale impact on the host ISM, 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 RG to understand how radio sources may regulate the star formation in their host galaxies. We present deep Spitzer IRS high-resolution spectroscopy of 8 nearby RG that show fast HI outflows. Strikingly, all of these HI-outflow RG have bright H_2 mid-IR lines that cannot be accounted for by UV or X-ray heating. This strongly suggests that the radio jet, which drives the HI outflow, is also responsible for the shock-excitation of the warm H_2 gas. In addition, the warm H_2 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 [NeII]12.8μm) are systematically broader than the H_2 lines, which are resolved by the IRS in ≈ 60% of the detected lines (with FWHM up to 900 km s^(-1)). In 5 sources, 3C 236, 3C 293, 3C 459, 4C 12.50 and PKS 1549-79, the [NeII]λ12.8μm line, and to a lesser extent the [NeIII]λ15.5μm and [NeV]λ14.3μm lines, clearly exhibit blue-shifted wings (up to -900 km s^(-1) with respect to the systemic velocity) that match well the kinematics of the outflowing HI or ionized gas. The H_2 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 HI gas, the H_2 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.

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