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 SCUBAselected 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 μm centroid, and also within 1.5 arcsec of a 44 μJy 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 submm/FIR luminosity of CUDSS14A is very weakly dependent on redshift within the constrained range, and is roughly 4×10 L⊙ (for H0=75 and an assumed Arp220-like spectrum), which implies a star-formation rate ∼1000 M⊙ yr . We derive an approximate gas mass of ∼ 10 M⊙ which would imply the current starforming activity cannot be sustained for longer than about 10 million years. With the present data however we are unable to rule out a significant AGN contribution to the total luminosity.