ALMA Deep Field in SSA22: A near-infrared-dark submillimeter galaxy at z=4.0
Abstract
Deep surveys with Atacama Large Millimeter Array (ALMA) have uncovered a population of dusty star-forming galaxies which are faint or even undetected at optical to near-infrared wavelengths. Their faintness at short wavelengths makes detailed characterization of the population challenging. Here we present a spectroscopic redshift identification and characterization of one of such near-infrared-dark galaxy discovered by an ALMA deep survey. Detection of [CI](1-0) and CO(4-3) emission lines determines the precise redshift of the galaxy, ADF22.A2, to be z=3.9913+/-0.0008. On the basis of multi-wavelength analysis, ADF22.A2 is found to be a massive, star-forming galaxy with stellar mass Mstar = 1.1-0.6+1.3 x 1011 Msun and SFR = 430-150+230 Msun/yr. The molecular gas mass is derived to be M (H2) = 5.9 +/- 1.5x1010 Msun, indicating a gas fraction of ~35%, and the ratios of L [CI](1-0)/L IR and L [CI](1-0)/L CO(4-3) suggests that the nature of the interstellar medium in ADF22.A2 is in accordance with those of other bright submillimeter galaxies. The properties of ADF22.A2, including redshift, star-formation rate, stellar mass, and depletion time scale (tau~0.1-0.2 Gyr), also suggest that ADF22.A2 has the characteristics expected for the progenitors of quiescent galaxies at z>3. Our results demonstrate the power of ALMA contiguous mapping and line scan to obtain an unbiased view of galaxy formation in the early Universe.