A LABOCA survey of submillimeter galaxies behind galaxy clusters

Onsala Space ObservatoryDepartment of Earth and Space Sciences, Chalmers University of Technology, 439 92 Onsala, Sweden
e-mail: daniel.p.johansson@chalmers.se

Received: 13 November 2010
Accepted: 24 December 2010

Abstract

Context. 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.

Aims. 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.

Methods. We use the LABOCA bolometer camera on the APEX telescope to observe five clusters of galaxies at a wavelength of 870 μm. The final maps have an angular resolution of 27.5″ and a point source noise level of 1.2–2.2 mJy. 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 24 μm sources in four of the fields for a stacking analysis.

Results. 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 870 μm signal of 390 ± 27 μJy at 14.5σ significance. We study the S_24   μm–S_870   μm relation by stacking on subsamples of the 24 μm sources and find a linear relation at S_24   μm < 300   μJy, followed by a flattening at higher 24 μm 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%.