The LABOCA/ACT Survey of Clusters at All Redshifts: Multiwavelength Analysis of Background Submillimeter Galaxies

Abstract

We present a multiwavelength analysis of 48 submillimeter galaxies (SMGs) detected in the Large APEX Bolometer Camera/Atacama Cosmology Telescope (ACT) Survey of Clusters at All Redshifts, LASCAR, which acquired new 870 μ m and Australia Telescope Compact Array 2.1 GHz observations of 10 galaxy clusters detected through their Sunyaev–Zel’dovich effect (SZE) signal by the ACT. Far-infrared observations were also conducted with the Photodetector Array Camera and Spectrometer (100/160 μ m) and SPIRE (250/350/500 μ m) instruments on Herschel for sample subsets of five and six clusters. LASCAR 870 μ m maps were reduced using a multiscale iterative pipeline that removes the SZE increment signal, yielding point-source sensitivities of σ  ∼ 2 mJy beam −1 . We detect in total 49 sources at the 4 σ level and conduct a detailed multiwavelength analysis considering our new radio and far-IR observations plus existing near-IR and optical data. One source is identified as a foreground galaxy, 28 SMGs are matched to single radio sources, four have double radio counterparts, and 16 are undetected at 2.1 GHz but tentatively associated in some cases to near-IR/optical sources. We estimate photometric redshifts for 34 sources with secure (25) and tentative (9) matches at different wavelengths, obtaining a median . Compared to previous results for single-dish surveys, our redshift distribution has a comparatively larger fraction of sources at z  > 3, and the high-redshift tail is more extended. This is consistent with millimeter spectroscopic confirmation of a growing number of high- z SMGs and relevant for testing of cosmological models. Analytical lens modeling is applied to estimate magnification factors for 42 SMGs at clustercentric radii >1.′2; with the demagnified flux densities and source-plane areas, we obtain integral number counts that agree with previous submillimeter surveys.