Resolving the Cosmic Far-Infrared Background at 450 and 850 Microns with SCUBA-2

TL;DR

This study uses deep SCUBA-2 observations to measure the cosmic far-infrared background at 450 and 850 microns, revealing the contributions of faint galaxies and resolving a significant portion of the background light.

Contribution

It provides the deepest measurements to date of the number counts at 450um and 850um, and assesses the contribution of faint sources to the cosmic infrared background.

Findings

Measured 113.9 Jydeg^{-2} of EBL at 450um, mainly from 1-10mJy sources.

Measured 37.3 Jydeg^{-2} of EBL at 850um, with a large uncertainty range.

Found a low fraction of blended sources (~12.5%) at 850um, with no significant multiplicity correction needed.

Abstract

We use the SCUBA-2 submillimeter camera mounted on the JCMT to obtain extremely deep number counts at 450 and 850um. We combine data on two cluster lensing fields, A1689 and A370, and three blank fields, CDF-N, CDF-S, and COSMOS, to measure the counts over a wide flux range at each wavelength. We use statistical fits to broken power law representations to determine the number counts. This allows us to probe to the deepest possible level in the data. At both wavelengths our results agree well with the literature in the flux range over which they have been measured, with the exception of the 850um counts in CDF-S, where we do not observe the counts deficit found by previous single-dish observations. At 450um, we detect significant counts down to ~1mJy, an unprecedented depth at this wavelength. By integrating the number counts above this flux limit, we measure 113.9^{+49.7}_{-28.4} Jydeg^{-2} of the 450um extragalactic background light (EBL). The majority of this contribution is from sources with S_450um between 1-10mJy, and these sources are likely to be the ones that are analogous to the local luminous infrared galaxies (LIRGs). At 850um, we measure 37.3^{+21.1}_{-12.9} Jydeg^{-2} of the EBL. Because of the large systematic uncertainties on the COBE measurements, the percentage of the EBL we resolve could range from 48%-153% (44%-178%) at 450 (850)um. Based on high-resolution SMA observations of around half of the 4sigma 850um sample in CDF-N, we find that 12.5^{+12.1}_{-6.8}% of the sources are blends of multiple fainter sources. This is a low multiple fraction, and we find no significant difference between our original SCUBA-2 850um counts and the multiplicity corrected counts.