Constraining the Thermal Dust Content of Lyman-Break Galaxies in an Overdense Field at z~5

We have carried out 870 micron observations in the J1040.7-1155 field, known to host an overdensity of Lyman break galaxies at z=5.16 +/- 0.05. We do not detect any individual source at the S(870)=3.0 mJy/beam (2 sigma) level. A stack of nine spectroscopically confirmed z>5 galaxies also yields a non-detection, constraining the submillimeter flux from a typical galaxy at this redshift to S(870)<0.85 mJy, which corresponds to a mass limit M(dust)<1.2x10^8 M_sun (2 sigma). This constrains the mass of thermal dust in distant Lyman break galaxies to less than one tenth of their typical stellar mass. We see no evidence for strong submillimeter galaxies associated with the ultraviolet-selected galaxy overdensity, but cannot rule out the presence of fainter, less massive sources.