2011A&A...527A.117J

Submillimeter galaxies are a population of dusty star-forming galaxies at high redshift. Measuring their properties will help relate them to other types of galaxies, both at high and low redshift. This is needed in order to understand the formation and evolution of galaxies. The aim is to use gravitational lensing by galaxy clusters to probe the faint and abundant submillimeter galaxy population down to a lower flux density level than what can be achieved in blank-field observations. We use the LABOCA bolometer camera on the APEX telescope to observe five clusters of galaxies at a wavelength of 870µm. The final maps have an angular resolution of 27.5'' and a point source noise level of 1.2-2.2mJy. We model the mass distribution in the clusters as superpositions of spherical NFW halos and derive magnification maps that we use to calculate intrinsic flux densities as well as area-weighted number counts. We also use the positions of Spitzer MIPS 24µm sources in four of the fields for a stacking analysis.We detected 37 submm sources, out of which 14 have not been previously reported. One source has a sub-mJy intrinsic flux density. The derived number counts are consistent with previous results, after correction for gravitational magnification and completeness levels. The stacking analysis reveals an intrinsic 870µm signal of 390 ±27µJy at 14.5σ significance. We study the S_24µm-S_870µm relation by stacking on subsamples of the 24µm sources and find a linear relation at S_24µm<300µJy, followed by a flattening at higher 24µm flux densities. The signal from the significantly detected sources in the maps accounts for 13% of the Extragalactic Background Light discovered by COBE, and the stacked signal accounts for 11%.