JET-POWERED MOLECULAR HYDROGEN EMISSION FROM RADIO GALAXIES

Abstract

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