Faint ALMA 1.2mm sources down to ~0.02mJy

Explorer observations. These results suggest that the major 1.2mm EBL contributors are sources with 0.02mJy, and that very faint 1.2mm sources with <~0.02mJy contribute negligibly to the EBL with the possible flattening and/or truncation of number counts in this very faint flux regime. To understand the physical origin of our faint ALMA sources, we measure the galaxy bias b_g_ by the counts-in-cells technique, and place a stringent upper limit of b_g_<3.5 that is not similar to b_g_ values of massive distant red galaxies and submillimeter galaxies but comparable to those of UV-bright, star-forming BzK galaxies (sBzKs) and Lyman break galaxies (LBGs).

Moreover, in the optical and near-infrared (NIR) deep fields, we identify optical-NIR counterparts for 59% of our faint ALMA sources, the majority of which have luminosities, colors, and the IRX-{beta} relation the same as sBzKs and LBGs. We thus conclude that about a half of our faint ALMA sources are dust-poor, high-z galaxies as known as sBzKs and LBGs in optical studies, and that these faint ALMA sources are not miniature (U)LIRGs simply scaled down with the infrared brightness.