SCUBA-2 Ultra Deep Imaging EAO Survey (STUDIES): Faint-end Counts at 450 m

The SCUBA-2 Ultra Deep Imaging EAO Survey (STUDIES) is a three-year JCMT Large Program aiming to reach the 450 m confusion limit in the COSMOS-CANDELS region to study a representative sample of the high-redshift far-infrared galaxy population that gives rise to the bulk of the far-infrared background. We present the first-year data from STUDIES. We reached a 450 m noise level of 0.91 mJy for point sources at the map center, covered an area of 151 arcmin2, and detected 98 and 141 sources at 4.0 and 3.5 , respectively. Our derived counts are best constrained in the 3.5-25 mJy regime using directly detected sources. Below the detection limits, our fluctuation analysis further constrains the slope of the counts down to 1 mJy. The resulting counts at 1-25 mJy are consistent with a power law having a slope of −2.59 ( 0.10 for 3.5-25 mJy, and − 0.7 + 0.4 for 1-3.5 mJy). There is no evidence of a faint-end termination or turnover of the counts in this flux density range. Our counts are also consistent with previous SCUBA-2 blank-field and lensing-cluster surveys. The integrated surface brightness from our counts down to 1 mJy is 90.0 17.2 Jy deg−2, which can account for up to 83 − 16 + 15 % of the COBE 450 m background. We show that Herschel counts at 350 and 500 m are significantly higher than our 450 m counts, likely caused by its large beam and source clustering. High angular resolution instruments like SCUBA-2 at 450 m are therefore highly beneficial for measuring the luminosity and spatial density of high-redshift dusty galaxies.