Depletion of background galaxies owing to the cluster lens CL0024+1654: U- and R-band observations

We have obtained U and R band observations of the depletion of background galaxies due to the gravitational lensing of the galaxy cluster CL0024+1654 (z = 0.39). The radial depletion curves show a significant depletion in both bands within a radius of 40 '' − 70 '' from the cluster center. This is the first time depletion is detected in the U band. This gives independent evidence for a break in the slope of the U band lu- minosity function at faint magnitudes. The radially averaged R band depletion curve is broader and deeper than in the U band. The differences can be attributed to the wavelength dependence of the slope of the luminosity function and to the different redshift distribution of the objects probed in the two bands. We estimate the Ein- stein radius, rE, of a singular isothermal sphere lens model using maximum likelihood analysis. Adopting a slope of the number counts of α = 0.2 and using the background density found beyond r = 150 '' we find rE = 17 '' ± 3 '' and rE = 25 '' ± 3 '' in the U and R band, respectively. When combined with the redshift of the single background galaxy at z = 1.675 seen as four giant arcs around 30 '' from the cluster center, these values indicate a median redshift in the range h zSi ≈ 0.7 to 1.1 for the UAB≥ 24 mag and RAB≥ 24 mag populations.