Thursday, July 18, 2013

1307.4576 (V. Casasola et al.)

A gas-rich AGN near the centre of a galaxy cluster at z ~ 1.4    [PDF]

V. Casasola, L. Magrini, F. Combes, A. Mignano, E. Sani, R. Paladino, F. Fontani
The formation of first virialized structures in overdensities dates back to ~9 Gyr ago, i.e., in the redshift range z ~ 1.4 - 1.6. At that epoch, some models of structure formation predict that the star formation activity in clusters was high, implying large reservoirs of cold molecular gas. Aiming at finding a trace of such expected high molecular gas content in primeval clusters, we searched for the 12CO(2-1) line emission in the most luminous active galactic nucleus (AGN) of the cluster around the radio galaxy 7C 1756+6520 at z ~ 1.4, one of the farthest spectroscopic confirmed clusters. This AGN, called AGN.1317, is located in the neighborhood of the central radio galaxy at a projected distance of ~780 kpc. The IRAM Plateau de Bure Interferometer was used to investigate the molecular gas quantity in AGN.1317, observing the 12CO(2-1) emission line. We detect CO emission in an AGN belonging to a galaxy cluster at z ~ 1.4. We measured a molecular gas mass of 1.1 x 10^10 Msun, comparable to that found in submillimeter galaxies. In optical images, AGN.1317 does not seem to be part of a galaxy interaction or merger.We also derived the nearly instantaneous SFR from Halpha flux obtaining SFR~65 Msun/yr. This suggests that AGN.1317 is actively forming stars and would exhaust its reservoir of cold gas in ~0.2-1.0 Gyr.
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