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 450µm map (1σ ≈ 1.3 mJy) from the SCUBA-2 Cosmology Legacy Survey (S2CLS), conducted with the James Clerk Maxwell Telescope (JCMT) is presented. Our map covers 140 arcmin 2 of the Cosmological Evolution Survey (COSMOS) field, in the footprint of the Hubble Space Telescope (HST) Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS). Using 60 submillimetre galaxies (SMGs) detected at 3.75σ, we evaluate the number counts of 450µm-selected galaxies with flux densities S 450 > 5 mJy. The 8 ′′ JCMT beam and high sensitivity of SCUBA-2 now make it possible to directly resolve a larger fraction of the cosmic infrared background (CIB, peaking at λ ∼ 200µm) into the individual galaxies responsible for its emission than has previously been possible at this wavelength. At S 450 > 5 mJy we resolve (7.4 ± 0.7) × 10 −2 MJy sr −1 of the CIB at 450µm (equivalent to 16 ± 7% of the absolute brightness measured by the Cosmic Background Explorer at this wavelength) into point sources. A further ∼40% of the CIB can be recovered through a statistical stack of 24µm emitters in this field, indicating that the majority (≈60%) of the CIB at 450µm is emitted by galaxies with S 450 > 2 mJy. The average redshift of 450µm emitters identified with an optical/near-infrared counterpart is estimated to be z = 1.3, implying that the galaxies in the sample are in the ultraluminous class (L IR ≈ 1.1 × 10 12 L ⊙ ). If the galaxies contributing to the statistical stack lie at similar redshifts, then the majority of the CIB at 450µm is emitted by galaxies in the LIRG class with L IR > 3.6 × 10 11 L ⊙ .

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