The SCUBA-2 Large eXtragalactic Survey: 850μm map, catalogue and the bright-end number counts of the XMM-LSS field

Garratt, T. K.; Geach, J. E.; Tamura, Y.; Coppin, K. E. K.; Franco, M.; Ao, Y.; Chen, C. -C.; Cheng, C.; Clements, D. L.; Dai, Y. S.; Dannerbauer, H.; Greve, T. R.; Hatsukade, B.; Hwang, H. S.; Jiang, L.; Kohno, K.; Koprowski, M. P.; Michałowski, M. J.; Sawicki, M.; Scott, D.; Shim, H.; Takeuchi, T. T.; Wang, W. -H.; Xue, Y. Q.; Yang, C.
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Monthly Notices of the Royal Astronomical Society

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We present $850\, \mu {\rm m}$ imaging of the XMM-LSS field observed for 170 h as part of the James Clerk Maxwell Telescope SCUBA-2 Large eXtragalactic Survey (S2LXS). S2LXS XMM-LSS maps an area of $9\, {\rm deg}^2$, reaching a moderate depth of $1\sigma \simeq 4\, {\rm mJy\, beam^{-1}}$. This is the largest contiguous area of extragalactic sky mapped by James Clerk Maxwell Telescope (JCMT) at $850\, \mu {\rm m}$ to date. The wide area of the S2LXS XMM-LSS survey allows us to probe the ultra-bright ($S_{\rm 850\mu m}\gtrsim 15\, {\rm mJy}$), yet rare submillimetre population. We present the S2LXS XMM-LSS catalogue, which comprises 40 sources detected at >5σ significance, with deboosted flux densities in the range of $7$-$48\, {\rm mJy}$. We robustly measure the bright-end of the $850\, \mu {\rm m}$ number counts at flux densities ${\gt }7\, {\rm mJy}$, reducing the Poisson errors compared to existing measurements. The S2LXS XMM-LSS observed number counts show the characteristic upturn at bright fluxes, expected to be motivated by local sources of submillimetre emission and high-redshift strongly lensed galaxies. We find that the observed $850\, \mu {\rm m}$ number counts are best reproduced by model predictions that include either strong lensing or source blending from a 15-arcsec beam, indicating that both may make an important contribution to the observed overabundance of bright single dish $850\, \mu {\rm m}$ selected sources. We make the S2LXS XMM-LSS $850\, \mu {\rm m}$ map and >5σ catalogue presented here publicly available.