Dust-enshrouded galaxies uncovered by ALMA deep surveys

Recent ALMA observations have unveiled the presence of faint (i.e., sub-mJy at lambda ~ 1mm, significantly fainter than the classical bright submillimeter galaxies), dusty star-forming galaxies, which are often invisible in the deepest near-infrared images taken with the Hubble Space Telescope (HST) and 8-10m class ground-based facilities. They seem to represent the bulk population of massive galaxies at z>3-4 and beyond, which have been completely missed by the Lyman break galaxy selection using HST/WFC3. Due to its faintness, however, detailed physical characterization of the faint dusty star-forming population remains a challenge. Here I report the initial outcomes of the ALMA lensing cluster survey (ACLS), one of the cycle-6 large programs of ALMA. It aims at obtaining high-resolution (~arcsec) images of high-magnification regions of 33 lensing clusters at 1.2-mm in Band-6 with a depth of ~80 uJy (1 sigma). The sample is taken from the best-studied massive clusters including CLASH, HFF, and RELICS. We have detected 134 continuum sources above 5 sigma, and we find a significant number of near-infrared-dark, magnified (but intrinsically faint) dusty star-forming galaxies within the ALCS images. In this talk, I will present some highlights including a cycle-7 follow-up program to characterize the triply imaged near-infrared-dark ALMA source, and the detection of a highly magnified [CII] line emitter at z = 6.02, which is the first spectroscopically confirmed sub-L* galaxy beyond z > 6 that straddles the critical curve.