  Submillimeter galaxies (SMG) represent a dust-obscured high-redshift
population undergoing massive star formation activity. Their properties and
space density have suggested that they may evolve into spheroidal galaxies
residing in galaxy clusters. In this paper, we report the discovery of compact
(~10"-20") galaxy overdensities centered at the position of three SMGs detected
with the Max-Planck Millimeter Bolometer camera (MAMBO) in the COSMOS field.
These associations are statistically significant. The photometric redshifts of
galaxies in these structures are consistent with their associated SMGs; all of
them are between z=1.4-2.5, implying projected physical sizes of ~170 kpc for
the overdensities. Our results suggest that about 30% of the radio-identified
bright SMGs in that redshift range form in galaxy density peaks in the crucial
epoch when most stars formed.
