Millimeter and radio observations of z ∼ 6 quasars

We present millimeter and radio observations of 13 SDSS quasars at redshifts z ∼ 6. We observed 11 of them with the Max Planck Millimeter Bolometer Array (MAMBO-2) at the IRAM 30 m telescope at 250 GHz and all of them with the Very Large Array (VLA) at 1.4 GHz. Four sources are detected by MAMBO-2 and six are detected by the VLA at the ≳ 3 σ level. These sources, together with another six published in previous papers, yield a submillimeter/millimeter- and radio-observed SDSS quasar sample at z ∼ 6. We use this sample to investigate the far-infrared (FIR) and radio properties of optically bright quasars in the early universe. We compare this sample to lower redshift samples of quasars observed in the submillimeter and millimeter wavelengths [(sub)mm] and find that the distribution of the FIR - to - B-band optical luminosity ratio (L_FIRL_B) is similar from z ∼ 2 to 6. We find a weak correlation between the FIR luminosity (L_FIR) and B-band optical luminosity (L_B) by including the (sub)mm observed samples at all redshifts. Some strong (sub)mm detections in the z ∼ 6 sample have radio-to-FIR ratios within the range defined by star-forming galaxies, which suggests possible coeval star-forming activity with the powerful AGN in these sources. We calculate the rest-frame radio-to-optical ratios (R _1.4* = L_v,1.4GHz/L_{v,4400 Å}) for all of the VLA-observed sources in the z ∼ 6 quasar sample. Only one radio detection in this sample, J083643.85+005453.3, has R_1.4* ∼ 40 and can be considered radio-loud. There are no strong radio sources (R _1.4* ≥ 100) among these SDSS quasars at z ∼ 6. These data are consistent with, although do not set strong constraints on, a decreasing radio-loud quasar fraction with increasing redshift.