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

TL;DR

This study uses SMA observations to detect and analyze faint submillimeter galaxies in lensing clusters, revealing a bimodal distribution in their properties and suggesting many are highly obscured or at high redshift.

Contribution

First SMA detections of intrinsically faint 850 μm sources in lensing clusters, revealing bimodal flux ratios and high dust obscuration in low-luminosity SMGs.

Findings

Most faint SMGs are extremely dusty or at high redshift.

Detected SMGs show a bimodal distribution in flux ratios.

Future ALMA observations will clarify the bimodality.

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.