The Ultra-Deep Survey

Determining the epoch of spheroid formation

We propose an ultradeep survey covering 0.77 sq. degs to 5 sigma point-source limits of K=23, H=24 and J=25. This will give a thousand-fold increase in area compared to any previous survey to this depth, which we anticipate will leave a lasting scientific legacy comparable to the impact made by the Hubble Deep Field. A major motivation is to determine the comoving number density of massive elliptical galaxies at high redshift (z>2) and hence discriminate between competing theories for their formation. Previous IR surveys to this depth, covering only several square arcminutes, have been unable to address this question. With the unique capabilities of WFCAM we can unambiguously test whether the most massive galaxies are already in place at z=3, or whether they form at lower redshifts through the mergers of less massive Lyman-break objects.