Characterisation of SCUBA-2 450um and 850um-selected Galaxies in the COSMOS Field

TL;DR

This study provides detailed submillimeter observations of galaxies in the COSMOS field, revealing their properties, redshift distribution, and the limitations of single-wavelength surveys in capturing the full population of high-redshift star-forming galaxies.

Contribution

It offers the first comprehensive comparison of 450um and 850um selected galaxies, highlighting their similarities, differences, and the incompleteness of single-wavelength surveys.

Findings

78 sources detected at 450um, 99 at 850um

Only 44% of 450um and 60% of 850um sources have counterparts at 24um or radio wavelengths

450um-selected galaxies are generally warmer with median dust temperatures 8-12K higher

Abstract

We present deep 450um and 850um observations of a large, uniformly covered 394arcmin^2 area in the COSMOS field obtained with the SCUBA-2 instrument on the James Clerk Maxwell Telescope (JCMT). We achieve root-mean-square noise values of 4.13mJy at 450um and 0.80mJy at 850um. The differential and cumulative number counts are presented and compared to similar previous works. Individual point sources are identified at >3.6sigma significance, a threshold corresponding to a 3-5% sample contamination rate. We identify 78 sources at 450um and 99 at 850um, with flux densities S450=13-37mJy and S850=2-16mJy. Only 62-76% of 450um sources are 850um detected and 61-81% of 850um sources are 450um detected. The positional uncertainties at 450um are small (1-2.5") and therefore allow a precise identification of multiwavelength counterparts without reliance on detection at 24um or radio wavelengths; we find that only 44% of 450um-selected galaxies and 60% of 850um-sources have 24um or radio counterparts. 450um-selected galaxies peak at <z>=1.95+-0.19 and 850um=selected galaxies peak at <z>=2.16+-0.11. The two samples occupy similar parameter space in redshift and luminosity, while their median SED peak wavelengths differ by ~10-50um (translating to deltaTdust =8-12K, where 450um-selected galaxies are warmer). The similarities of the 450um and 850um populations, yet lack of direct overlap between them, suggests that submillimeter surveys conducted at any single far-infrared wavelength will be significantly incomplete (~>30%) at censusing infrared-luminous star formation at high-z.