Rest-frame optical and far-infrared observations of extremely bright Lyman-break galaxy candidates at z~2.5

We have investigated the rest-frame optical and far-infrar ed properties of a sample of extremely bright candidate Lyman-break galaxies (LBG) identified in the Sloan Digital Sky Survey. Their high ultraviolet luminosities and lack of str ong ultraviolet emission lines are suggestive of massive starbursts, although it is possible t hat they are more typical luminosity LBGs which have been highly magnified by strong gravitationa l lensing. Alternatively, they may be an unusual class of weak-lined quasars. If the ultraviolet and submillimetre properties of these objects mirror those of less luminous, starbur st LBGs, then they should have detectable rest-frame far-infrared emission. However, our submm photometry fails to detect such emission, indicating that these systems are not merely scaled-up (either intrinsically or as a result of lensing) examples of typical LBGs. In addition we have searched for the morphological signatures of strong lensing, using high-resol ution, near-infrared imaging, but we find none. Instead, near-infrared spectroscopy reveals tha t these systems are, in fact, a rare class of broad absorption-line (BAL) quasars.