Redshift distributions of the galaxies in and surrounding the overdensity. Top: distribution of redshifts, determined from the emission-line spectra of blue (Y − K_s < 2) galaxies taken with the FORS2 and VIMOS instruments on the Very Large Telescope. The insert shows a more detailed histogram for the range z = 2−2.15. For galaxies in the peak, the spectra sample the rest-frame  ~1200–2200 Å. Bottom: distribution of photometric redshifts of red (Y − K_s > 2) galaxies within the central 20′′. These were estimated by comparing the BIRzYJHK_s+IRAC spectral energy distribution to a set of spectral synthesis models computed from templates of half-solar, solar, and twice-solar metallicity and assuming two different types of star-formation history (exponentially declining and constant truncated). We did not include the effects of dust attenuation, as the colour, morphological, and spectral properties of the red galaxies point strongly towards them being dominated by passive stellar populations rather than dust-reddened younger stars.