The UV galaxy luminosity function at z=3-5 from the CFHT Legacy Survey Deep fields

Aims. We measure and study the evolution of the UV galaxy luminosity function (LF) at z = 3-5 from the largest high-redshift survey to date, the Deep part of the CFHT Legacy Survey. We also give accurate estimates of the SFR density at these redshifts. Methods. We consider similar to 100 000 Lyman-break galaxies at z approximate to 3.1, 3.8 and 4.8 selected from very deep ugriz images of this data set and estimate their rest-frame 1600 angstrom luminosity function. Due to the large survey volume, cosmic variance plays a negligible role. Furthermore, we measure the bright end of the LF with unprecedented statistical accuracy. Contamination fractions from stars and low-z galaxy interlopers are estimated from simulations. From these simulations the redshift distributions of the Lyman-break galaxies in the different samples are estimated, and those redshifts are used to choose bands and calculate k-corrections so that the LFs are compared at the same rest-frame wavelength. To correct for incompleteness, we study the detection rate of simulated galaxies injected to the images as a function of magnitude and redshift. We estimate the contribution of several systematic effects in the analysis to test the robustness of our results. Results. We find the bright end of the LF of our u-dropout sample to deviate significantly from a Schechter function. If we modify the function by a recently proposed magnification model, the fit improves. For the first time in an LBG sample, we can measure down to the density regime where magnification affects the shape of the observed LF because of the very bright and rare galaxies we are able to probe with this data set. We find an increase in the normalisation, phi*, of the LF by a factor of 2.5 between z approximate to 5 and z approximate to 3. The faint-end slope of the LF does not evolve significantly between z approximate to 5 and z approximate to 3. We do not find a significant evolution of the characteristic magnitude in the studied redshift interval, possibly because of insufficient knowledge of the source redshift distribution. The SFR density is found to increase by a factor of similar to 2 from z approximate to 5 to z approximate to 4. The evolution from z approximate to 4 to z approximate to 3 is less eminent.