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Sub-mm Imaging of a Proto-cluster Region at Z = 3.09

We have used the Submillimetre Common-User Bolometer Array (SCUBA) detector on the James Clerk Maxwell Telescope (JCMT) to measure bright sub-mm emission associated with a recently discovered extensive (> 100h −1 kpc) and highly luminous, 'blob' of Ly α emission at z = 3.09. The blob lies within a known large overdensity of optical sources in the z = 3.07–3.11 range, and is centered on a locally overdense peak within this region. The best explanation for the copious sub-mm emission is a dust obscured continuum source, which may produce the ionizing flux for the Ly α cloud. Cooling gas explanations are plausible but excessively complicated , and the 450/850 µm ratio rules out a significant fraction of the signal arising from the Sunyaev-Zel'dovich increment. At least two additional ≃ 10 mJy sub-mm detections in the SCUBA map, with a surface density significantly higher than in blank field surveys, suggests that they may be associated with the z = 3.09 structure. A SCUBA 'photometry' observation of a second nearby Ly α blob tentatively detects a weaker sub-mm counterpart.