ALMA twenty-six arcmin${}^2$ survey of GOODS-S at one-millimeter (ASAGAO): Near-infrared-dark faint ALMA sources

Abstract

We report detections of two 1.2 mm continuum sources ($S_{1.2mm}$ ~ 0.6 mJy) without any counterparts in the deep $H$- and/or $K$-band image (i.e., $K$-band magnitude $\gtrsim$ 26 mag). These near-infrared-dark faint millimeter sources are uncovered by ASAGAO, a deep and wide-field ($\simeq$ 26 arcmin${}^2$) Atacama Large Millimeter/submillimeter Array (ALMA) 1.2 mm survey. One has a red IRAC (3.6 and 4.5 $\hat{I}¼$m) counterpart, and the other has been independently detected at 850 and 870 $\hat{I}¼$m using SCUBA2 and ALMA Band 7, respectively. Their optical to radio spectral energy distributions indicate that they can lie at $z\gtrsim$ 3-5 and can be in the early phase of massive galaxy formation. Their contribution to the cosmic star formation rate density is estimated to be ~ 1 $\times$ 10${}^{-3}$ $M_{\odot }$ yr${}^{-1}$ Mpc${}^{-3}$ if they lie somewhere in the redshift range of $z$ ~ 3-5. This value can be consistent with, or greater than that of bright submillimeter galaxies ($S_{870\hat{\mathrm{I}}¼\mathrm{m}}>$ 4.2 mJy) at $z$ ~ 3-5. We also uncover 3 more candidates near-infrared-dark faint ALMA sources without any counterparts ($S_{1.2mm}$ ~ 0.45-0.86 mJy). These results show that an unbiased ALMA survey can reveal the dust-obscured star formation activities, which were missed in previous deep optical/near-infrared surveys.

10 pages, 6 figures, accepted for publication in ApJ