to infer the real-space correlation lengths. In Section 4 we use photometric redshifts to derive a luminosity function for these populations, and compare with the present-day galaxy luminosity function. A discussion and conclusions are presented in Section 5. Throughout this paper we assume a flat $\Lambda$CDM cosmology with $\Omega_m = 0.3$ and $h = 0.73$.

Source identification and number counts
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Data set and sample definitions
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![BzK colour-colour diagram for sources in the UDS DR1. The sBzK and pBzK selection regions are marked accordingly. Also visible are the passive galaxy track identified in [@Lane_etal:2007], and the stellar locus used to match our photometric system to that of [@Daddi_etal:2004] (see text). We show mean error-bars for the galaxies in the BzK selection regions.[]{data-label="bzk"}](PSfiles/UDS_DR1_BzK_v1.3_daddifilters.ps){width="240pt"}

The UKIRT Infrared Deep Sky Survey (UKIDSS) has been underway since spring 2005 and comprises 5 sub-surveys covering a range of areas and depths [@Lawrence_etal:2007]. This survey has been made possible by the advent of the UKIRT Wide-Field Camera [@Casali_etal:2007].

We base the present study on data from the deepest component of UKIDSS, the Ultra Deep Survey (Almaini et al. in preparation). This aims to reach final depths of $K_{AB} = 25.0, H_{AB} = 25.4, J_{AB} =
