2004ApJ...613L.113B

Using the IRAM Plateau de Bure Interferometer, we have searched for CO (3-2) emission from the dusty Lyman break galaxy Westphal-MD11 at z=2.98. Our sensitive upper limit is surprisingly low relative to the system's 850 µm flux density and implies a far-IR/CO luminosity ratio as elevated as those seen in local ultraluminous mergers. We conclude that the observed dust emission must originate in a compact structure radiating near its blackbody limit and that a relatively modest molecular gas reservoir must be fueling an intense nuclear starburst (and/or deeply buried active nucleus) that may have been triggered by a major merger. In this regard, Westphal-MD11 contrasts strikingly with the lensed Lyman break galaxy MS 1512-cB58, which is being observed apparently midway through an extended episode of more quiescent disk star formation.