HerMES: SPIRE galaxy number counts at 250, 350 and 500 microns

TL;DR

This paper presents galaxy number counts at 250, 350, and 500 microns from Herschel observations, providing key data to test galaxy evolution models and resolve a portion of the infrared background.

Contribution

It offers the first precise galaxy counts at these wavelengths from Herschel, serving as a benchmark for galaxy evolution models and resolving part of the infrared background.

Findings

Galaxy counts show a steep rise below 100 mJy.

Resolved 15% of the infrared extragalactic background.

Counts are consistent with previous fluctuation analysis estimates.

Abstract

Emission at far-infrared wavelengths makes up a significant fraction of the total light detected from galaxies over the age of Universe. Herschel provides an opportunity for studying galaxies at the peak wavelength of their emission. Our aim is to provide a benchmark for models of galaxy population evolution and to test pre-existing models of galaxies. With the Herschel Multi-tiered Extra-galactic survey, HerMES, we have observed a number of fields of different areas and sensitivity using the SPIRE instrument on Herschel. We have determined the number counts of galaxies down to ~20 mJy. Our constraints from directly counting galaxies are consistent with, though more precise than, estimates from the BLAST fluctuation analysis. We have found a steep rise in the Euclidean normalised counts at <100 mJy. We have directly resolved 15% of the infrared extra-galactic background at the wavelength near where it peaks.