Thermal Emission from Warm Dust in the Most Distant Quasars
Ran Wang, Chris L. Carilli, Jeff Wagg, Frank Bertoldi, Fabian Walter, Karl M. Menten, Alain Omont, Pierre Cox, Michael A. Strauss, Xiaohui Fan, Linhua Jiang, Donald P. Schneider
We report new continuum observations of fourteen z 6 quasars at 250 GHz and fourteen quasars at 1.4 GHz. We summarize all recent millimeter and radio observations of the sample of the thirty-three quasars known with 5.71<=z<=6.43, and present a study of the rest frame far-infrared (FIR) properties of this sample. These quasars were observed with the Max Plank Millimeter Bolometer Array (MAMBO) at 250 GHz with mJy sensitivity, and 30 them were detected. We also recover the average 250 GHz flux
... nsity of the MAMBO undetected sources at 4 sigma, by stacking the on-source measurements. The derived mean radio-to-UV spectral energy distributions (SEDs) of the full sample and the 250 GHz non-detections show no significant difference from that of lower-redshift optical quasars. Obvious FIR excesses are seen in the individual SEDs of the strong 250 GHz detections, with FIR-to-radio emission ratios consistent with that of typical star forming galaxies. Most 250 GHz-detected sources follow the L_FIR--L_bol relationship derived from a sample of local IR luminous quasars (L_IR>10^12L_), while the average L_FIR/L_bol ratio of the non-detections is consistent with that of the optically-selected PG quasars. The MAMBO detections also tend to have weaker Lyα emission than the non-detected sources. We discuss possible FIR dust heating sources, and critically assess the possibility of active star formation in the host galaxies of the z 6 quasars. The average star formation rate of the MAMBO non-detections is likely to be less than a few hundred M_ yr^-1, but in the strong detections, the host galaxy star formation is probably at a rate of ≳10^3 M_ yr^-1, which dominates the FIR dust heating.