The Canada-France High-z Quasar Survey: 1.2 mm observations

We report 250 GHz (1.2 mm) 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 Millmétrique (IRAM). An rms sensitivity of ≲0.6 mJy was achieved for 65% of the sample, and of ≲1.0 mJy for 90%. Only one quasar, CFHQS J142952+544717, was robustly detected with S_{250 GHz} = 3.46 ± 0.52 mJy. 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 1.2 mm flux density ⟨ S_{250 GHz} ⟩ = 0.41 ± 0.14 mJy; 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 ± 0.32 × 10¹² L_⊙, and an average star formation rate of a few 100 M_⊙/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.