2018ApJ...865..106C

We analyze the >4σ sources in the most sensitive 100 arcmin² area (rms < 0.56 mJy) of a SCUBA-2 850 µm survey of the GOODS-S and present the 75 band-7 ALMA sources (>4.5σ) obtained from high-resolution interferometric follow-up observations. The raw SCUBA-2 >4σ limit is fainter than 2.25 mJy throughout this region, and deboosting corrections would lower this further. Of the 53 SCUBA-2 sources in this sample, only five have no ALMA detections, while 13% (68% confidence range 7%-19%) have multiple ALMA counterparts. Color-based high-redshift dusty galaxy selection techniques find at most 55% of the total ALMA sample. In addition to using literature spectroscopic and optical/near-infrared photometric redshifts, we estimate far infrared photometric redshifts based on an Arp 220 template. We identify seven z >= 4 candidates. We see the expected decline with redshift of the 4.5 and 24 µm to 850 µm flux ratios, confirming these as good diagnostics of z >= 4 candidates. We visually classify 52 ALMA sources, finding 44% (68% confidence range 35%-53%) to be apparent mergers. We calculate rest-frame 2-8 keV and 8-28 keV luminosities using the 7 Ms Chandra X-ray image. Nearly all of the ALMA sources detected at 0.5-2 keV are consistent with a known X-ray luminosity to 850 µm flux relation for star-forming galaxies, while most of those detected at 2-7 keV are moderate-luminosity AGNs that lie just above the 2-7 keV detection threshold. The latter largely have substantial obscurations of logN_H=23–24 cm^–2, but two of the high-redshift candidates may even be Compton thick.