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

Abstract

We have used SCUBA to survey an area of simeq 50 arcmin2, detecting 19 sources down to a 3 σ sensitivity limit of ~3.5 mJy at 850 μm. Monte Carlo simulations have shown that the fluxes of sources in this and similar SCUBA surveys are biased upward by the effects of source confusion and noise, leading to an overestimate by a factor of ~1.4 in the fraction of the 850 μm 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 microjansky radio sources, and two are ISO 15 μm sources. The radio/submillmeter flux ratios imply that the dust in these galaxies is being heated by young stars rather than active galactic nuclei. The upper limit to the average 450 μm/850 μm flux ratio implies either that the SCUBA galaxies are at z G 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 submillimeter luminosity density reach a maximum at some redshift? (3) If the SCUBA sources are protoellipticals, 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 acceptable models in which very little star formation occurred before a redshift of 3 (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.