Jet-Powered Molecular Hydrogen Emission from Radio Galaxies
  H2 pure-rotational emission lines are detected from warm (100-1500 K)
molecular gas in 17/55 (31% of) radio galaxies at redshift z<0.22 observed with
the Spitzer IR Spectrograph. The summed H2 0-0 S(0)-S(3) line luminosities are
L(H2)=7E38-2E42 erg/s, yielding warm H2 masses up to 2E10 Msun. These radio
galaxies, of both FR radio morphological types, help to firmly establish the
new class of radio-selected molecular hydrogen emission galaxies (radio
MOHEGs). MOHEGs have extremely large H2 to 7.7 micron PAH emission ratios:
L(H2)/L(PAH7.7) = 0.04-4, up to a factor 300 greater than the median value for
normal star-forming galaxies. In spite of large H2 masses, MOHEGs appear to be
inefficient at forming stars, perhaps because the molecular gas is
kinematically unsettled and turbulent. Low-luminosity mid-IR continuum emission
together with low-ionization emission line spectra indicate low-luminosity AGNs
in all but 3 radio MOHEGs. The AGN X-ray emission measured with Chandra is not
luminous enough to power the H2 emission from MOHEGs. Nearly all radio MOHEGs
belong to clusters or close pairs, including 4 cool core clusters (Perseus,
Hydra, A 2052, and A 2199). We suggest that the H2 in radio MOHEGs is delivered
in galaxy collisions or cooling flows, then heated by radio jet feedback in the
form of kinetic energy dissipation by shocks or cosmic rays.
