The SCUBA-2 Cosmology Legacy Survey: blank-field number counts of 450-μm-selected galaxies and their contribution to the cosmic infrared background

Abstract

The first deep blank-field 450um map (1-sigma~1.3mJy) from the SCUBA-2\nCosmology Legacy Survey (S2CLS), conducted with the James Clerk Maxwell\nTelescope (JCMT) is presented. Our map covers 140 arcmin^2 of the COSMOS field,\nin the footprint of the HST CANDELS area. Using 60 submillimetre galaxies\n(SMGs) detected at >3.75-sigma, we evaluate the number counts of 450um-selected\ngalaxies with flux densities S_450>5mJy. The 8-arcsec JCMT beam and high\nsensitivity of SCUBA-2 now make it possible to directly resolve a larger\nfraction of the cosmic infrared background (CIB, peaking at ~200um) into the\nindividual galaxies responsible for its emission than has previously been\npossible at this wavelength. At S_450>5mJy we resolve (7.4[+/-]0.7)x10^-2\nMJy/sr of the CIB at 450um (equivalent to 16[+/-]7% of the absolute brightness\nmeasured by COBE at this wavelength) into point sources. A further ~40% of the\nCIB can be recovered through a statistical stack of 24um emitters in this\nfield, indicating that the majority (~60%) of the CIB at 450um is emitted by\ngalaxies with S_450>2mJy. The average redshift of 450um emitters identified\nwith an optical/near-infrared counterpart is estimated to be <z>=1.3, implying\nthat the galaxies in the sample are in the ultraluminous class (L_IR~1.1x10^12\nL_sun). If the galaxies contributing to the statistical stack lie at similar\nredshifts, then the majority of the CIB at 450um is emitted by galaxies in the\nLIRG class with L_IR>3.6x10^11 L_sun.\n