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

We present a high-resolution millimetre interferometric image of the bright est 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 a nd 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 e nergy distribution and conclude that it lies within the redshift range 2 < z < 4.5. The submillimetre/far-infrared luminosity of CUDSS14A is very weak ly 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 cu rrent 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 significan t AGN contribution to the total luminosity.