Starburst galaxies and structure in the submillimetre background towards the Hubble Deep Field

We use an 850-mum SCUBA map of the Hubble Deep Field (HDF) to study the dus t properties of optically-selected starburst galaxies at high redshift. The optical/infrared (IR) data in the HDF allow a photometric redshift to be e stimated for each galaxy, together with an estimate of the visible star-for mation rate. The 850-mum flux density of each source provides the complemen tary information: the amount of hidden, dust-enshrouded star formation acti vity. Although the 850-mum map does not allow detection of the majority of individual sources, we show that the galaxies with the highest UV star-form ation rates are detected statistically, with a flux density of about S-850 = 0.2 mJy for an apparent UV star-formation rate of 1 h(-2) M. yr(-1). This level of submillimetre output indicates that the total star-forming activi ty is on average a factor of approximately 6 times larger than the rate inf erred from the UV output of these galaxies, The general population of optic al starbursts is then predicted to contribute at least 25 per cent of the 8 50-mum background. We carry out a power-spectrum analysis of the map, which yields some evidence for angular clustering of the background source popul ation, but at a level lower than that seen in Lyman-break galaxies. Togethe r with other lines of argument, particularly from the NICMOS HDF data, this suggests that the 850-mum background originates over an extremely wide ran ge of redshifts - perhaps 1 less than or similar to z less than or similar to 6.