The Hawaii SCUBA-2 Lensing Cluster Survey: Are Low-luminosity Submillimeter Galaxies Detected in the Rest-frame UV?

Abstract

In this third paper of the Hawaii SCUBA-2 Lensing Cluster Survey series, we present Submillimeter Array (SMA) detections of six intrinsically faint 850 $\mu$m sources detected in SCUBA-2 images of the lensing cluster fields, A1689, A2390, A370, MACS J0717.5+3745, and MACS J1423.8+2404. Two of the SCUBA-2 sources split into doublets, yielding a total of eight SMA detections. The intrinsic 870 $\mu$m flux densities of these submillimeter galaxies (SMGs) are $\sim$ 1 mJy. Five of the eight SMGs are not detected in optical or near-infrared (NIR) images. The NIR-to-submillimeter flux ratios of these faint SMGs suggest that most of them are extremely dusty and/or at very high redshifts. Combining these SMGs and several other samples from the literature, we find a bimodal distribution for the faint sources in the space of submillimeter flux versus NIR-to-submillimeter flux ratio. While most of the SMA-detected lensed sources are very obscured, the other SMGs with similar flux densities are mostly bright in the NIR. Future ALMA observations of a large sample of SCUBA-2 sources in cluster fields will allow us to decide whether the bimodality we observe here really exists.

9 pages, 4 figures, 6 tables. Accepted for publication in ApJ

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• JWST reveals a population of ultra-red, flattened disk galaxies at 2<z<6 previously missed by HST
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• A Multiwavelength Study of ELAN Environments (AMUSE${}^2$): Ubiquitous dusty star-forming galaxies associated with enormous Ly$\alpha$ nebulae on megaparsec scales
• JADES Ultra-red Flattened Objects: Morphologies and Spatial Gradients in Color and Stellar Populations
• A Submillimeter Survey of Faint Galaxies Behind Ten Strong Lensing Clusters