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We have used SCUBA to survey an area of 50 square arcmin, detecting 19sources down to a 3sigma sensitivity limit of 3.5 mJy at 850 microns. We haveused Monte-Carlo simulations to assess the effect of source confusion and noiseon the SCUBA fluxes and positions, finding that the fluxes of sources in theSCUBA surveys are significantly biased upwards and that the fraction of the 850micron background that has been resolved by SCUBA has been overestimated. Theradio/submillmetre flux ratios imply that the dust in these galaxies is beingheated by young stars rather than AGN. We have used simple evolution modelsbased on our parallel SCUBA survey of the local universe to address the majorquestions about the SCUBA sources: (1) what fraction of the star formation athigh redshift is hidden by dust? (2) Does the submillimetre luminosity densityreach a maximum at some redshift? (3) If the SCUBA sources areproto-ellipticals, when exactly did ellipticals form? However, we show that theobservations are not yet good enough for definitive answers to these questions.There are, for example, acceptable models in which 10 times as muchhigh-redshift star formation is hidden by dust as is seen at opticalwavelengths, but also acceptable ones in which the amount of hidden starformation is less than that seen optically. There are acceptable models inwhich very little star formation occurred before a redshift of three (as mightbe expected in models of hierarchical galaxy formation), but also ones in which30% of the stars have formed by this redshift. The key to answering thesequestions are measurements of the dust temperatures and redshifts of the SCUBAsources.Comment: 41 pages (latex), 17 postscript figures, to appear in the November  issue of the Astronomical Journa

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