A NEW WINDOW ON GALAXY FORMATION AND EVOLUTION.

during 1997 july/august, we conducted the first deep survey of the sky at submm wavelengths using the new scuba submm camera (smail, ivison & blain 1997). our submm maps cover a total area of 20 arcmin^2 to 1sigma noise levels less than 13 and 2 mjy/beam at 450 and 850um. we have concentrated on lensing clusters to exploit the amplification of background sources by the cluster, improving the sensitivity by a factor of 1.32.0 as compared with a blankfield survey. a cumulative source surface density of 2400 +/ 1000 per square degree is found to a 50% completeness limit of 4 mjy at 850um. the submm spectral properties of these sources indicate that the majority lie at high redshift, z >> 1. without correcting for lens amplification, our observations place a firm upper limit on the blankfield counts at this depth. this surface density is 3 orders of magnitude greater than the expectation of a nonevolving model using the local iras 60um luminosity function. the observed source counts thus require a substantial increase in the number density of strongly starforming galaxies in the highredshift universe. the magnitude of this increase indicates that optical surveys of the starformation properties of the distant universe have missed substantial numbers of obscured starforming galaxies. this provides strong constraints on the formation of normal galaxies. clearly, the consequences of these observations are extremely farreaching and it is vital that we obtain followup multifrequency observations of the detected sources to determine where they fit in to our picture of galaxy evolution. already, we have obtained extremely deep b, v, r, i and kband images and deep x, c and lband radio maps. these show that the detected sources have extremely red spectral energy distributions and do not have active nuclei. here, we request an allocation of 20ks to determine their restframe mid truncated!, Please see act [truncated!, Please see actual data for full text]