The SCUBA Bright Quasar Survey ( SBQS ) : 850 micron observations of the z > ∼ 4 sample

We present initial results of a new, systematic search for massive star-formation in the host galaxies of the most luminous and probably most massive z>∼4 radio-quiet quasars (MB ≤ −27.5; νLν(1450Å) > 10 13 L⊙). The survey, undertaken at 850μm using SCUBA at the James Clerk Maxwell Telescope (JCMT), has a target sensitivity limit of 3σ ∼10mJy, set to identify sources suitable for detailed follow-up e.g. continuum mapping and molecular line diagnostics. A total of 38 z>∼4 radio-quiet quasars have been observed at 850μm, of which 8 were detected (>3σ) with S850μm >∼ 10mJy (submillimetre-loud). The new detections almost triple the number of optically selected, submillimetre-loud z>∼4 radio-quiet quasars known to date. We include a detailed description of how our quasar sample is defined in terms of radio and optical properties. As a by-product of our selection procedure we have identified 17 radio-loud quasars with z>∼4. There is no strong evidence for trends in either detectability or 850μm flux with absolute magnitude, MB. We find that the weighted mean flux of the undetected sources is 2.0± 0.6mJy, consistent with an earlier estimate of ∼ 3mJy based on more sensitive observations of a sample z>∼4 radio-quiet quasars (McMahon et al.,1999). This corresponds to an inferred starformation rate of ∼1000M⊙ yr −1 , similar to Arp220. The typical starformation timescale for the submillimetre-bright sources is ∼ 1Gyr, 10 times longer than the typical accretion-driven e-folding timescale of ∼ 5 × 10 years. Our 850μm detection of the z = 4.4 quasar PSS J1048+4407 when analysed in conjunction with 1.2mm single-dish and interferometric observations suggests that this source is resolved on angular scales of 1-2(6-12 kpc). In addition, we present a new optical spectrum of this source, identifying it as a broad absorption line (BAL) quasar. The new redshift is outside that covered in a recent CO line search by Guilloteau et al., (1999), highlighting the need for accurate redshifts for the obervation and interpretation of high-redshift line studies.