The Canada-UK Deep Submillimeter Survey: IV. The Survey of the 14-Hour Field

We have used SCUBA to survey an area of ≃ 50 arcmin2, detecting 19 sources down to a 3σ sensitivity limit of ∼3.5 mJy at 850μm. Monte-Carlo simulations have shown that the fluxes of sources in this and similar SCUBA surveys are biased upwards by the effects of source confusion and noise, leading to an overestimate by a factor of ∼1.4 in the fraction of the 850μm background that has been resolved by SCUBA. Once a correction is made for this effect, about 20% of the background has been resolved. The simulations have also been used to quantify the effects of confusion on source positions. Of the 19 SCUBA sources, five are μJy radio sources and two are ISO 15μm sources. The radio/submillmetre flux ratios imply that the dust in these galaxies is being heated by young stars rather than AGN. The upper limit to the average 450μm/850μm flux ratio implies either that the SCUBA galaxies are at z >> 2 or, if they are at lower redshifts, that the dust is generally colder than in ULIRGs. We have used simple evolution models to address the major questions about the SCUBA sources: (1) what fraction of the star formation at high redshift is hidden by dust? (2) Does the submillimetre luminosity density reach a maximum at some redshift? (3) If the SCUBA sources are proto-ellipticals, when exactly did ellipticals form? We show, however, that the observations are not yet good enough to answer these questions. There are, for example, acceptable models in which 10 times as much high-redshift star formation is hidden by dust as is seen at optical wavelengths, but also acceptable ones in which the amount of hidden star formation is less than that seen optically. There are also acceptable models in which very little star formation occurred before a redshift of three (as might be expected in models of hierarchical galaxy formation), but also ones in which 30% of the stars have formed by this redshift. The key to answering these questions are measurements of the dust temperatures and redshifts of the SCUBA sources. Subject headings: galaxies: evolution — galaxies: formation — infrared: galaxies — cosmology: observations — surveys Department of Physics and Astronomy, Cardiff University, P.O. Box 913, Cardiff CF2 3YB, UK Department of Astronomy, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 1A1, Canada National Radio Astronomy Observatory, P.O. Box 0, 1003 Lopezville Road, Socorro, NM 87801