Energetics of the molecular gas in the H_2 luminous radio galaxy 3C 326:
  Evidence for negative AGN feedback
  We present a detailed analysis of the gas conditions in the H_2 luminous
radio galaxy 3C326N at z~0.1, which has a low star formation rate (SFR~0.07
M_sun/yr) in spite of a gas surface density similar to those in starburst
galaxies. Its star-formation efficiency is likely a factor ~20-30 lower than
those of ordinary star-forming galaxies. Combining new IRAM CO emission-line
interferometry with existing Spitzer mid-infrared spectroscopy, we find that
the luminosity ratio of CO and pure rotational H_2 line emission is factors
10-100 lower than what is usually found. This may suggest that most of the
molecular gas is warm. The Na D absorption-line profile of 3C326N in the
optical suggests an outflow with a terminal velocity of ~ -1800 km/s and a mass
outflow rate of 30-40 M_sun/yr, which cannot be explained by star formation.
The mechanical power implied by the wind, of order 10^43 erg/s, is comparable
to the bolometric luminosity of the emission lines of ionized and molecular
gas. To explain these observations, we propose a scenario where a small
fraction of the mechanical energy of the radio jet is deposited in the the
interstellar medium of 3C326N, which powers the outflow, and the line emission
through a mass momentum and energy exchange between the different phases in the
ISM. Dissipation times are of order 10^7-8 yrs, similar or greater than the
typical jet lifetime. Small ratios of CO and PAH surface brightnesses in
another 7 H_2 luminous radio galaxies suggest that a similar form of AGN
feedback could be lowering star formation efficiencies in these galxies a
similar way. The local demographics of radio-loud AGN suggests that secular gas
cooling in massive early-type galaxies of >= 10^11 M_sun could be regulated
through a fundamentally similar form of 'maintenance-phase' AGN feedback.
