Observing strategies for blank-field surveys in the submillimetre waveband

Abstract

The coming generation of submillimetre bolometer array detectors, such as the Submillimetre Common-User Bolometer Array (SCUBA) instrument currently 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 the submillimetre waveband requirea careful assessment of the optimum observing strategy, aimed both at maximizing the probabilities of detecting distant galaxies and at discriminating between different models of galaxy formation and evolution. The distinctive feature of faint submillimetre sources is that their predicted source counts are inverted at low flux densities and this strongly influences the observing strategy. We illustrate how the strategy differs for distinct models of the evolution of the population of star-forming galaxies. In all cases the preferred observing wavelength is 850 μn. plausible models of the evolution of IRAS galaxies suggest that the best strategy would be to observe an area of about 0.1 deg2 for an observing time of 3 × 105 s. In a hierarchical clustering picture, it would be preferable to observe a much smaller area of 0.01 deg2 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.