The colour selection of distant galaxies in the UKIDSS Ultra Deep Survey Early Data Release

We investigate colour selection techniques for high-redshift galaxies in the UKIRT Infrared Deep Sky Survey (UKIDSS) Ultra Deep Survey Early Data Release (UDS EDR). Combined with very deep Subaru optical photometry, the depth (KAB= 22.5) and area (0.62 deg2) of the UDS EDR allow us to investigate optical/near-infrared selection using a large sample of over 30 000 objects. By using the B−z′, z′−K colour–colour diagram (the BzK technique) we identify over 7500 candidate galaxies at z > 1.4, which can be further separated into passive and star-forming systems (pBzKs and sBzKs respectively). Our unique sample allows us to identify a new feature not previously seen in BzK diagrams, consistent with the passively evolving track of early-type galaxies at z 1 galaxies over a narrow redshift range