We investigate colour selection techniques for high redshift galaxies in the UKIDSS Ultra Deep Survey Early Data Release ( UDS EDR ) .
Combined with very deep Subaru optical photometry , the depth ( K _ { AB } = 22.5 ) and area ( 0.62 deg ^ { 2 } ) of the UDS EDR allows us to investigate optical/near-IR 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 starforming systems ( pBzK and sBzK 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 < 1.4 .
We also compare the BzK technique with the R - K colour selection of Extremely Red Objects ( EROs ) and the J - K selection of Distant Red Galaxies ( DRGs ) , and quantify the overlap between these populations .
We find that the majority of DRGs , at these relatively bright magnitudes are also EROs .
Since previous studies have found that DRGs at these magnitudes have redshifts of z \sim 1 we determine that these DRG/ERO galaxies have SEDs consistent with being dusty star-forming galaxies or AGN at z < 2 .
Finally we observe a flattening in the number counts of pBzK galaxies , similar to other studies , which may indicate that we are sampling the luminosity function of passive z > 1 galaxies over a narrow redshift range .