The SCUBA Bright Quasar Survey (SBQS) - II. Unveiling the quasar epoch at submillimetre wavelengths

Abstract

We present results of the first systematic search for submillimetre (submm) continuum emission from z ∼ 2, radio-quiet, optically-luminous (M B < -27.5) quasars, using the SCUBA array camera on the James Clerk Maxwell Telescope (JCMT). We have observed a homogeneous sample of 57 quasars in the redshift range 1.5 < z < 3.0 - the epoch during which the comoving density of luminous active galactic nuclei (AGN) peaks - to make a systematic comparison with an equivalent sample at high redshift (z > 4; Paper I). The target sensitivity of the survey, 3σ = 10 mJy at 850 (μm, was chosen to enable efficient identification of bright submm sources, suitable for detailed follow-up. Nine targets are detected with 3σ significance or greater, with fluxes in the range 7-17 mJy. Although the detection rate above 10 mJy is lower than that of the z > 4 survey, the weighted mean flux of the undetected sources, 1.9 ± 0.4 mJy, is similar to that at z > 4 (2.0 ± 0.6 mJy). The statistical significance of trends is analysed, and it is found that: (i) within the limited optical luminosity range studied, there is no strong evidence for a correlation between submm and optical luminosity; (ii) there is a suggestion of a variation of submm detectability with redshift, but that this is consistent with the K-correction of a characteristic far-infrared spectrum.