A new measurement of the evolving near-infrared galaxy luminosity function out to z ≃ 4: a continuing challenge to theoretical models of galaxy formation

We present the most accurate measurement to date of cosmological evolution of the near-infrared galaxy luminosity function, from the local Universe out to z similar or equal to 4. The analysis is based on a large and highly complete sample of galaxies selected from the first data release of the UKIDSS Ultra Deep Survey. Exploiting a master catalogue of K- and z-band selected galaxies over an area of 0.7 deg2, we analyse a sample of similar or equal to 50 000 galaxies, all with reliable photometry in 16 bands from the far-ultraviolet to the mid-infrared. The unique combination of a large area and depth provided by the Ultra Deep Survey allows us to trace the evolution of the K-band luminosity function with unprecedented accuracy. In particular, via a maximum-likelihood analysis we obtain a simple parametrization for the luminosity function and its cosmological evolution, including both luminosity and density evolution, which provides an excellent description of the data from z = 0 up to z similar or equal to 4. We find differential evolution for galaxies dependent on galaxy luminosity, revealing once again the 'downsizing behaviour' of galaxy formation. Finally, we compare our results with the predictions of the latest theoretical models of galaxy formation, based on both semi-analytical prescriptions and full hydrodynamical simulations.