Comparing SCUBA-2 and ALMA Selections of Faint Dusty Star-forming Galaxies in A2744

Abstract

We make a comparison of deep SCUBA-2 450 and 850 μm imaging on the massive lensing cluster field A2744 with Atacama Large Millimeter/submillimeter Array (ALMA) 1.2 mm data. Our primary goal is to assess how effective the wider-field SCUBA-2 sample, in combination with red JWST priors, is for finding faint dusty star-forming galaxies (DSFGs) compared to the much more expensive mosaicked ALMA observations. We cross-match our previously reported direct (>5σ) SCUBA-2 sample and red JWST NIRCam prior-selected (>3σ) SCUBA-2 sample to direct ALMA sources from the DUALZ survey. We find that roughly 95% are confirmed by ALMA. The red priors also allow us to probe deeper in the ALMA image. Next, by measuring the 450 and 850 μm properties of the full ALMA sample, we show that 46/69 of the ALMA sources are detected at 850 μm and 24/69 are detected at 450 μm in the SCUBA-2 images, with a total detection fraction of nearly 75%. All of the robust (>5σ) ALMA sources that are not detected in at least one SCUBA-2 band lie at 1.2 mm fluxes ≲0.6 mJy and are undetected primarily due to the higher SCUBA-2 flux limits. We also find that the SCUBA-2 detection fraction drops slightly beyond z = 3, which we attribute to the increasing 1.2 mm to 850 μm and 1.2 mm to 450 μm flux ratios combined with the ALMA selection. The results emphasize the power of combining SCUBA-2 data with JWST colors to map the faint DSFG population.