2013A&A...552A..43O

We report 250GHz (1.2mm) observations of a sample of 20 quasars at redshifts 5.8<z<6.5 from the Canada-France High-z Quasar Survey (CFHQS), using the Max-Planck-Millimeter-Bolometer (MAMBO) array at the 30-metre telescope of the Institut de Radioastronomie Millmetrique (IRAM). An rms sensitivity of ≲0.6mJy was achieved for 65% of the sample, and of ≲1.0mJy for 90%. Only one quasar, CFHQSJ142952+544717, was robustly detected with S_250GHz=3.46±0.52mJy. This indicates that one of the most powerful known starbursts at z∼6 is associated with this radio-loud quasar. On average, the other CFHQS quasars, which have a mean optical magnitude fainter than the previously studied samples of z∼6 quasars of the Sloan Digital Sky Survey (SDSS), have a mean 1.2mm flux density <S_250GHz≥0.41±0.14mJy; this average detection with a signal-to-noise (S/N) ratio of 2.9 is hardly meaningful. It would correspond to <L_FIR≥∼0.94±0.32x10¹²L_☉, and an average star formation rate of a few 100M_☉/yr, depending on the stellar initial mass function (IMF) and a possible contribution of an active galactic nucleus (AGN) to <L_FIR>. This is consistent with previous findings of Wang et al. on the far-infrared emission of z∼6 quasars and extends their results toward optically fainter sources.