NEPSC2, the North ecliptic pole SCUBA-2 survey: 850-μm map and catalogue of 850-μm-selected sources over 2 deg²

We present an 850-μm mosaic map and extracted catalogue of submillimetre sources in the extended North Ecliptic Pole (NEP) region over about 2 deg². The 850-μm map is constructed using newly obtained observations by SCUBA-2 at the East Asian Observatory's James Clerk Maxwell Telescope, carried out using the observatory's large programme opportunities. The recent 850-μm survey has extended the submillimetre data coverage by almost a factor of 4 compared to previous surveys, with a depth of σ_rms = 1.0-2.3 mJy beam⁻¹. The catalogue contains 549 sources selected above a significance level of 4σ, where the false-detection rate is 10 per cent; a higher threshold of 4.5σ is required in order to achieve a false-detection rate below 3 per cent, which results in 342 sources being selected. Despite the large spatial variation of the noise, the deboosted flux density of sources is comparable to results from the SCUBA-2 Cosmology Legacy Survey, which covered the central 0.6 deg² of our survey area with better sensitivity. We construct the source counts at 850 μm, finding results in agreement with other 850-μm surveys in cosmological blank fields over S₈₅₀ = 4-15 mJy. We find a slight excess of bright galaxies (S₈₅₀ > 15 mJy), which can be considered to be at z_phot = 2-4. The 850-μm data add valuable long-wavelength information to mid-infrared-selected sources from the AKARI NEP-deep and NEP-wide surveys, which will be helpful in preparing for future near-infrared to millimetre wavelength observations in the NEP region. Our 850-μm mosaic map and source catalogue will be made publicly available.