Energetics of the molecular gas in the H₂ luminous radio galaxy 3C 326: Evidence for negative AGN feedback

October 2010 • 2010A&A...521A..65N

Authors • Nesvadba, N. P. H. • Boulanger, F. • Salomé, P. • Guillard, P. • Lehnert, M. D. • Ogle, P. • Appleton, P. • Falgarone, E. • Pineau Des Forets, G.

Abstract • We present a detailed analysis of the gas conditions in the H₂ luminous radio galaxy 3C 326 N at z ~ 0.1, which has a low star-formation rate (SFR ~ 0.07 M_⊙ yr^-1) in spite of a gas surface density similar to those in starburst galaxies. Its star-formation efficiency is likely a factor ~10-50 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 H₂ line emission is factors 10-100 lower than what is usually found. This suggests that most of the molecular gas is warm. The Na D absorption-line profile of 3C 326 N in the optical suggests an outflow with a terminal velocity of ~-1800 km s^-1 and a mass outflow rate of 30-40 M_⊙ yr^-1, which cannot be explained by star formation. The mechanical power implied by the wind, of order 10⁴³ erg s^-1, 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 interstellar medium of 3C 326 N, which powers the outflow, and the line emission through a mass, momentum and energy exchange between the different gas phases of 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 H₂ luminous radio galaxies suggest that a similar form of AGN feedback could be lowering star-formation efficiencies in these galaxies in a similar way. The local demographics of radio-loud AGN suggests that secular gas cooling in massive early-type galaxies of ≥10¹¹ M_⊙ could generally be regulated through a fundamentally similar form of “maintenance-phase” AGN feedback.

Based on observations carried out with the IRAM Plateau de Bure Interferometer.

Links

• PREPRINT http://arxiv.org/abs/1003.3449
• NED https://ned.ipac.caltech.edu/uri/NED::InRefcode/2010A%26A...521A..65N
• POSTSCRIPT https://www.aanda.org/10.1051/0004-6361/200913333/postscript
• ELECTR https://doi.org/10.1051%2F0004-6361%2F200913333
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2010A%26A...521A..65N
• PDF https://www.aanda.org/10.1051/0004-6361/200913333/pdf
• DATA https://irsa.ipac.caltech.edu/bibdata/2010/N/2010A&A...521A..65N.html