Far-infrared and Molecular CO Emission from the Host Galaxies of Faint Quasars at z ~ 6

Ran Wang , Jeff Wagg , Chris L. Carilli , Roberto Neri , Fabian Walter , Alain Omont (1) , Dominik A. Riechers , Frank Bertoldi , Karl M. Menten , Pierre Cox , Michael A. Strauss , Xiaohui Fan , Linhua Jiang

1 IAP - Institut d'Astrophysique de Paris

We present new millimeter and radio observations of nine z ~ 6 quasars discovered in deep optical and near-infrared surveys. We observed the 250 GHz continuum in eight of the nine objects and detected three of them. New 1.4 GHz radio continuum data have been obtained for four sources, and one has been detected. We searched for molecular CO (6-5) line emission in the three 250 GHz detections and detected two of them. Combined with previous millimeter and radio observations, we study the far-infrared (FIR) and radio emission and quasar-host galaxy evolution with a sample of 18 z ~ 6 quasars that are faint at UV and optical wavelengths (rest-frame 1450 Å magnitudes of m ₁₄₅₀ >= 20.2). The average FIR-to-active galactic nucleus (AGN) UV luminosity ratio of this faint quasar sample is about two times higher than that of the bright quasars at z ~ 6 (m ₁₄₅₀ < 20.2). A fit to the average FIR and AGN bolometric luminosities of both the UV/optically faint and bright z ~ 6 quasars, and the average luminosities of samples of submillimeter/millimeter-observed quasars at z ~ 2-5, yields a relationship of L _FIR ~ L _bol ^0.62. Five of the 18 faint z ~ 6 quasars have been detected at 250 GHz. These 250 GHz detections, as well as most of the millimeter-detected optically bright z ~ 6 quasars, follow a shallower trend of L _FIR ~ L _bol ^0.45 defined by the starburst-AGN systems in local and high-z universe. The millimeter continuum detections in the five objects and molecular CO detections in three of them reveal a few × 10⁸ M _sun of FIR-emitting warm dust and 10¹⁰ M _sun of molecular gas in the quasar host galaxies. All these results argue for massive star formation in the quasar host galaxies, with estimated star formation rates of a few hundred M _sun yr^-1. Additionally, the higher FIR-to-AGN luminosity ratio found in these 250 GHz detected faint quasars also suggests a higher ratio between star formation rate and supermassive black hole accretion rate than the UV/optically most luminous quasars at z ~ 6.

Mots clés: galaxies: active; galaxies: high-redshift; galaxies: starburst; molecular data; quasars: general; Astrophysics - Cosmology and Nongalactic Astrophysics

Domaines: Planète et Univers [physics]

Ran Wang, Jeff Wagg, Chris L. Carilli, Roberto Neri, Fabian Walter, et al.. Far-infrared and Molecular CO Emission from the Host Galaxies of Faint Quasars at z ~ 6. The Astronomical Journal, 2011, 142, ⟨10.1088/0004-6256/142/4/101⟩. ⟨insu-03645894⟩