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 .