We report optical-infrared (IR) properties of faint 1.3 mm sources (S1.3mm = 0.2–1.0 mJy) detected with the Atacama Large Millimeter/submillimeter Array (ALMA) in the Subaru/XMM-Newton Deep Survey field. We searched for optical/IR counterparts of eight ALMA-detected sources (≥4.0σ, the sum of the probability of spurious source contamination is ~1) in a K-band source catalog. Four ALMA sources have K-band counterpart candidates within a 04 radius. Comparison between ALMA-detected and undetected K-band sources in the same observing fields shows that ALMA-detected sources tend to be brighter, more massive, and more actively forming stars. While many of the ALMA-identified submillimeter-bright galaxies (SMGs) in previous studies lie above the sequence of star-forming galaxies in the stellar mass–star formation rate plane, our ALMA sources are located in the sequence, suggesting that the ALMA-detected faint sources are more like "normal" star-forming galaxies rather than "classical" SMGs. We found a region where multiple ALMA sources and K-band sources reside in a narrow photometric redshift range (z ~ 1.3–1.6) within a radius of 5'' (42 kpc if we assume z = 1.45). This is possibly a pre-merging system and we may be witnessing the early phase of formation of a massive elliptical galaxy.
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