Program: GN-2010B-Q-115

We propose to continue our long-term search for high-redshift quasars in the UKIDSS LAS, and here set our final goal to coverage of 3000 sq degs. At the end of 09B we had completed 1500 sq degs, which we aim to extend to 1900, 2500, 3000 in 10A (underway), 10B (this proposal, 4hrs), 11A (to submit next round, 4hrs). Our search is sensitive over 5.8<z<7.2. The current status is that we have discovered 4 new quasars of z=5.72 (BAL), 5.94, 6.04, 6.13, and rediscovered the 3 SDSS quasars in the same area of z=5.82, 5.93, 6.22. Over the 1500 sq degs fully analysed we have discovered no quasars over the interval 6.4<z<7.2, whereas we predict 3.7. The discovery of no quasars is inconsistent with prediction at the 97.4% significance level. We aim to sharpen this result by completing 3000 sq degs, for which we predict 7.5 z>6.4 quasars. The discovery of no quasars in this area would be inconsistent with prediction at the 99.9% significance level. On the other hand any quasars discovered at 6.4<z<7.2 will provide vital new information on the evolution of the IGM neutral fraction at this epoch.