High spatial resolution observations of CUDSS14A: a SCUBA-selected ultraluminous galaxy at high redshift

We present a high-resolution millimetre interferometric image of the brightest SCUBA-selected galaxy from the Canada-UK Deep SCUBA survey (CUDSS). We make a very clear detection at 1.3 mm, but fail to resolve any structure in the source. The interferometric position is within 1.5 arcsec of the SCUBA 850-mu m centroid, and also within 1.5 arcsec of a 44-mu Jy radio source and a very faint, extremely red galaxy which we had previously identified as the submillimetre source. We also present new optical and infrared imaging, and infrared spectroscopy of this source. We model the overall spectral energy distribution and conclude that it lies within the redshift range 2 < z < 4.5. The submillimetre/far-infrared luminosity of CUDSS14A is very weakly dependent on redshift within the constrained range, and is roughly 4x10(12) L. (for H-0=75 km s(-1) Mpc(-1) and an assumed Arp 220-like spectrum), which implies a star formation rate similar to 1000 M. yr(-1). We derive an approximate gas mass of similar to 10(10) M. which would imply that the current star-forming activity cannot be sustained for longer than about 10(7) yr. With the present data, however, we are unable to rule out a significant AGN contribution to the total luminosity.