FAINT END OF 1.3 mm NUMBER COUNTS REVEALED BY ALMA

Abstract

We present the faint end of number counts at 1.3 mm (238 GHz) obtained with\nthe Atacama Large Millimeter/submillimeter Array (ALMA). Band 6 observations\nwere carried out targeting 20 star-forming galaxies at z ~ 1.4 in the\nSubaru/XMM-Newton Deep Survey field. In the observations, we serendipitously\ndetect 15 sources (>=3.8 sigma, S(1.3 mm) = 0.15-0.61 mJy) other than the\ntargeted sources. We create number counts by using these `sub-mJy sources',\nwhich probe the faintest flux range among surveys at millimeter wavelengths.\nThe number counts are consistent with (flux-scaled) number counts at 850 um and\n870 um obtained with gravitational lensing clusters. The ALMA number counts\nagree well with model predictions, which suggest that these sub-mJy populations\nare more like `normal' star-forming galaxies than `classical' SMGs with intense\nstar-forming activity. In this flux range, ~80% of the extragalactic background\nlight at 1.3 mm is resolved into individual sources.\n