OBSERVING STRATEGIES FOR BLANK-FIELD SURVEYS IN THE SUBMILLIMETER WAVEBAND

The coming generation of submillimetre bolometer array detectors, such as the Submillimetre Common-User Bolometer Array (SCUBA) instrument c urrently being constructed for the James Clerk Maxwell Telescope (JCMT ), offer opportunities for searching for distant star-forming galaxies in the submillimetre waveband. The special features of observing in t he submillimetre waveband require a careful assessment of the optimum observing strategy, aimed both at maximizing the probabilities of dete cting distant galaxies and at discriminating between different models of galaxy formation and evolution. The distinctive feature of faint su bmillimetre sources is that their predicted source counts are inverted at low flux densities and this strongly influences the observing stra tegy. We illustrate how the strategy differs for distinct models of th e evolution of the population of star-forming galaxies. In all cases t he preferred observing wavelength is 850 mu m. Plausible models of the evolution of IRAS galaxies suggest that the best strategy would be to observe an area of about 0.1 deg(2) for an observing time of 3x10(5) s. In a hierarchical clustering picture, it would be preferable to obs erve a much smaller area of 0.01 deg(2) for the same time to a deeper limiting flux density of 0.3 mJy, at which the extremely steep source counts expected in these models should be detected. It is argued that both types of survey should be carried out.