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

TL;DR

This paper presents a large 850um survey of the XMM-LSS field, cataloging bright submillimetre sources, measuring their number counts, and analyzing the effects of lensing and blending on observed source abundance.

Contribution

It provides the largest contiguous 850um map of the extragalactic sky, with a new catalogue of bright sources and refined number counts, highlighting the roles of lensing and blending.

Findings

Detected 40 sources >5-sigma significance.

Measured the bright-end of 850um number counts with reduced errors.

Model predictions including lensing or blending best match observed counts.

Abstract

We present 850um imaging of the XMM-LSS field observed for 170 hours as part of the James Clerk Maxwell Telescope SCUBA-2 Large eXtragalactic Survey (S2LXS). S2LXS XMM-LSS maps an area of 9 square degrees, reaching a moderate depth of 1-sigma ~ 4 mJy/beam. This is the largest contiguous area of extragalactic sky mapped by JCMT at 850um to date. The wide area of the S2LXS XMM-LSS survey allows us to probe the ultra-bright (S_850um > 15 mJy), yet rare submillimetre population. We present the S2LXS XMM-LSS catalogue, which comprises 40 sources detected at >5-sigma significance, with deboosted flux densities in the range of 7 mJy to 48 mJy. We robustly measure the bright-end of the 850um number counts at flux densities >7 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 850um 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 over-abundance of bright single dish 850um selected sources. We make the S2LXS XMM-LSS 850um map and >5-sigma catalogue presented here publicly available.