Submillimeter galaxies behind the Bullet cluster (1E 0657-56)

¹ Onsala Space Observatory, Chalmers University of Technology, 439 92 Onsala, Sweden e-mail: daniel.p.johansson@chalmers.se
² Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
³ Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁴ Department of Physics, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK
⁵ Instituto Nacional de Astrofísica, Optica y Electrónica (INAOE), Tonantzintla, Puebla 72840, Mexico
⁶ Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile

Received: 9 December 2009
Accepted: 19 February 2010

Abstract

Context. Clusters of galaxies are effective gravitational lenses able to magnify background galaxies and making it possible to probe the fainter part of the galaxy population. Submillimeter galaxies, which are believed to be star-forming galaxies at typical redshifts of 2 to 3, are a major contaminant to the extended Sunyaev-Zeldovich (SZ) signal of galaxy clusters. For a proper quantification of the SZ signal the contribution of submillimeter galaxies needs to be quantified.

Aims. The aims of this study are to identify submillimeter sources in the field of the Bullet cluster (1E 0657-56), a massive cluster of galaxies at z 0.3, measure their flux densities at 870 μm, and search for counterparts at other wavelengths to constrain their properties.

Methods. We carried out deep observations of the submillimeter continuum emission at 870 μm using the Large APEX BOlometer CAmera (LABOCA) on the Atacama Pathfinder EXperiment (APEX) telescope. Several numerical techniques were used to quantify the noise properties of the data and extract sources.

Results. In total, seventeen sources were found. Thirteen of them lie in the central 10 arcmin of the map, which has a pixel sensitivity of 1.2 mJy per 22'' beam. After correction for flux boosting and gravitational lensing, the number counts are consistent with published submm measurements. Nine of the sources have infrared counterparts in Spitzer maps. The strongest submm detection coincides with a source previously reported at other wavelengths, at an estimated redshift z 2.7. If the submm flux arises from two images of a galaxy magnified by a total factor of 75, as models have suggested, its intrinsic flux would be around 0.6 mJy, consistent with an intrinsic luminosity below 10¹² .