Absence of evidence is not evidence of absence: the colour–density relation at fixed stellar mass persists to z∼ 1

We use data drawn from the DEEP2 Galaxy Redshift Survey to investigate the relationship between local galaxy density, stellar mass and rest-frame galaxy colour. At z∼ 0.9, we find that the shape of the stellar mass function at the high-mass [ log 10(M*/h−2  M⊙) > 10.1] end depends on the local environment, with high-density regions favouring more massive systems. Accounting for this stellar mass–environment relation (i.e. working at fixed stellar mass), we find a significant colour–density relation for galaxies with 10.6 1.