HerMES: A search for high-redshift dusty galaxies in the HerMES Large Mode Survey - Catalogue, number counts and early results

TL;DR

This study used Herschel/SPIRE data over 274 square degrees to identify high-redshift dusty star-forming galaxies, creating a large catalogue that exceeds model predictions and confirming the effectiveness of flux-based selection methods.

Contribution

It presents a new large-area catalogue of high-redshift dusty galaxies selected via flux density criteria, expanding previous smaller surveys and providing the first detailed shape of red source counts.

Findings

Catalogue of 477 red sources with flux densities S_500 > S_350 > S_250

Number counts exceed galaxy evolution model predictions by an order of magnitude

Spectroscopic redshifts confirm high-redshift nature of selected sources

Abstract

Selecting sources with rising flux densities towards longer wavelengths from Herschel/SPIRE maps is an efficient way to produce a catalogue rich in high-redshift (z > 4) dusty star-forming galaxies. The effectiveness of this approach has already been confirmed by spectroscopic follow-up observations, but the previously available catalogues made this way are limited by small survey areas. Here we apply a map-based search method to 274 deg$^2$ of the HerMES Large Mode Survey (HeLMS) and create a catalogue of 477 objects with SPIRE flux densities $S_{500} > S_{350} >S_{250}$ and a $5 \sigma$ cut-off $S_{500} > $ 52 mJy. From this catalogue we determine that the total number of these "red" sources is at least an order of magnitude higher than predicted by galaxy evolution models. These results are in agreement with previous findings in smaller HerMES fields; however, due to our significantly larger sample size we are also able to investigate the shape of the red source counts for the first time. We have obtained spectroscopic redshift measurements for two of our sources using the Atacama Large Millimeter/submillimeter Array (ALMA). The redshifts z = 5.1 and z = 3.8 confirm that with our selection method we can indeed find high-redshift dusty star-forming galaxies.