Submillimeter imaging of a protocluster region at z=3.09

We have used the Submillimeter Common-User Bolometer Array (SCUBA) detector on the James Clerk Maxwell Telescope to measure bright submillimeter emission associated with a recently discovered extensive (>100 h(-1) kpc) and highly luminous "blob" of Ly alpha 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 submillimeter emission is a dust-obscured continuum source, which may produce the ionizing flux for the Ly alpha cloud. Cooling gas explanations are plausible but excessively complicated, and the 450/850 mum ratio rules out a significant fraction of the signal arising from the Sunyaev-Zeldovich increment. At least two additional similar or equal to 10 mJy submillimeter detections in the SCUBA map, with a surface density significantly higher than in blank-field surveys, suggest that they may be associated with the z = 3.09 structure. A SCUBA "photometry" observation of a second nearby Ly alpha blob tentatively detects a weaker submillimeter counterpart.