2018ApJ...855...26A

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 µm 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 µm) and SPIRE (250/350/500 µm) instruments on Herschel for sample subsets of five and six clusters. LASCAR 870 µm 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 4σ 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 z=2.8_–1.7^+2.1. 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.