2024ApJ...971..117G

We present confusion-limited SCUBA-2 450 μm 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 μm cover an area of 450 arcmin². We achieved instrumental noise levels of σ₄₅₀ = 0.59 mJy beam^–1 and σ₈₅₀ = 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 4σ (3.5σ) threshold, we detected 360 (479) sources at 450 μm and 237 (314) sources at 850 μm. We derive the deepest blank-field number counts at 450 μm, 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 μm 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 μm down to 2.1 mJy to be ${57.3}_{-6.2}^{+1.0}$ Jy deg^–2, contributing to 41% ± 4% of the 450 μm extragalactic background light (EBL) measured by Cosmic Background Explorer and Planck. Our results suggest that the 450 μm 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.