Extragalactic number counts at 100 um, free from cosmic variance

TL;DR

This study uses Herschel data to measure extragalactic number counts at 100 um, achieving cosmic variance independence and confirming previous results with no significant variance detected.

Contribution

It provides the first cosmic variance independent measurement of 100 um extragalactic counts using Herschel data across multiple small fields.

Findings

Results are consistent with previous small-area surveys.

No statistically significant cosmic variance detected.

Implications for galaxy source confusion in debris disc studies.

Abstract

We use data from the Disc Emission via a Bias-free Reconnaissance in the Infrared/Submillimetre (DEBRIS) survey, taken at 100 um with the Photoconductor Array Camera and Spectrometer instrument on board the Herschel Space Observatory, to make a cosmic variance independent measurement of the extragalactic number counts. These data consist of 323 small-area mapping observations performed uniformly across the sky, and thus represent a sparse sampling of the astronomical sky with an effective coverage of ~2.5 deg^2. We find our cosmic variance independent analysis to be consistent with previous count measurements made using relatively small area surveys. Furthermore, we find no statistically significant cosmic variance on any scale within the errors of our data. Finally, we interpret these results to estimate the probability of galaxy source confusion in the study of debris discs.