SCUBA-2 Ultra Deep Imaging EAO Survey (STUDIES). V. Confusion-limited Submillimeter Galaxy Number Counts at 450 μm and Data Release for the COSMOS Field

Abstract

We present confusion-limited SCUBA-2 450 μ m observations in the COSMOS-CANDELS region as part of the James Clerk Maxwell Telescope Large Program SCUBA-2 Ultra Deep Imaging EAO Survey. Our maps at 450 and 850 μ m cover an area of 450 arcmin ^2 . We achieved instrumental noise levels of σ _450 = 0.59 mJy beam ^−1 and σ _850 = 0.09 mJy beam ^−1 in the deepest area of each map. The corresponding confusion noise levels are estimated to be 0.65 and 0.36 mJy beam ^−1 . Above the 4 σ (3.5 σ ) threshold, we detected 360 (479) sources at 450 μ m and 237 (314) sources at 850 μ m. We derive the deepest blank-field number counts at 450 μ m, covering the flux-density range of 2–43 mJy. These are in agreement with other SCUBA-2 blank-field and lensing-cluster observations but are lower than various model counts. We compare the counts with those in other fields and find that the field-to-field variance observed at 450 μ m at the $R=6^{\prime} $ scale is consistent with Poisson noise, so there is no evidence of strong 2D clustering at this scale. Additionally, we derive the integrated surface brightness at 450 μ m down to 2.1 mJy to be ${57.3}_{-6.2}^{+1.0}$ Jy deg ^−2 , contributing to 41% ± 4% of the 450 μ m extragalactic background light (EBL) measured by Cosmic Background Explorer and Planck. Our results suggest that the 450 μ m EBL may be fully resolved at ${0.08}_{-0.08}^{+0.09}$ mJy, which extremely deep lensing-cluster observations and next-generation submillimeter instruments with large aperture sizes may be able to achieve.

Keywords

• Catalogs
• Cosmic background radiation
• Galaxy evolution
• High-redshift galaxies
• Submillimeter astronomy