Is there a redshift cutoff for submillimetre galaxies?

We present new optical and infrared photometry for a statistically complete sample of seven 1.1 mm selected sources with accurate coordinates. We determine photometric redshifts for four of the seven sources of 4.64, 4.54, 1.49 and 0.18. Of the other three sources two are undetected at optical wavelengths down to the limits of very deep Subaru and Canada-France-Hawaii Telescope images (∼27 mag AB, i band) and the remaining source is obscured by a bright nearby galaxy. The sources with the highest redshifts are at higher redshifts than all but one of the ∼200 sources taken from the largest recent 850 μm surveys, which may indicate that 1.1 mm surveys are more efficient at finding sources at very high redshifts than 850 μm surveys. We investigate the evolution of the number density with redshift of our sample using a banded Ve/Va analysis and find no evidence for a redshift cutoff, although the number of sources is very small. We also perform the same analysis on a statistically complete sample of 38 galaxies selected at 850μm from the GOODS-N field and find evidence for a drop-off in the number density beyond z ∼ 1 and 2, confirming the earlier conclusion of Wall, Pope & Scott (2008). We also find evidence for the existence of two differently evolving sub-populations separated in luminosity, with the drop-off in density for the low-luminosity sources occurring at a lower redshift.