SCUBA Deep Fields and Source Confusion

Deep submillimetre(submm)-wave surveys made over the last three years using the SCUBA camera at the 15-m James Clerk Maxwell Telescope (JCMT) have revealed a new population of very luminous high-redshift galaxies. The properties of this population, and their contribution to the intensity of the extragalactic background radiation field are described briefly, especially in the context of the SCUBA lens survey. The potential problems caused by source confusion in the large 15-arcsec SCUBA observing beam for the identification and follow up of the results are discussed. The effects of confusion are not important for the study of 850-μm SCUBA sources brighter than about 2mJy. High-redshift surveys for dusty galaxies In 1997 the SCUBA camera at the JCMT [31] became available, providing deep images of 5-arcmin fields at 450 and 850μm, and allowing the first deep blank-field searches for redshifted thermal dust emission from distant galaxies. By exploiting the positive magnification bias and rich archival data in the fields of seven massive clusters of galaxies, 15 non-cluster sources and 2 cD galaxies [24] were soon detected in the SCUBA Lens Survey [40,44] and several sources were identified [3,41], three having certain identifications and redshifts based on mm-wave CO spectroscopy [26,27,34]. Several other deep surveys in clusters [19,35] and non-cluster fields [5,32,23,21] have confirmed the existence of this population of distant galaxies. Three SCUBA-selected galaxies from all these surveys, without CO detections, have accurate positions from mm-wave continuum interferometry. [20,28,29] Targeted SCUBA observations to image or obtain submm-wave photometry in the fields of both faint radio sources with very faint K-band counterparts [4,18] and known high-redshift objects [33,17,38,1] have increased the number of submm-selected galaxies known. In the first approach, the wide fields and accurate astrometry available from deep radio surveys is exploited to reveal relatively bright submm-selected galaxies [4]. In the second, valuable redshifts are available for the detected submm sources. A summary of the published submm-wave counts at both 850 and 450μm is presented in Fig. 1, alongside the contribution of the SCUBA Lens Survey galaxies to the integrated background radiation intensity derived from observations using COBE [25]. At 850μm, a significant fraction of the background 1 The SCUBA Lens Survey has been carried out since 1997 by Ian Smail, Rob Ivison, Jean-Paul Kneib and the author: a full description of the survey and references to supporting work can be found in the recent catalogue paper [44]