CARS: The CFHTLS-Archive-Research Survey III. First detection of cosmic
  magnification in samples of normal high-z galaxies
  Weak gravitational lensing (WL) has been established as one of the most
promising probes of cosmology. So far, most studies have exploited the shear
effect of WL leading to coherent distortions of galaxy shapes. But WL also
introduces coherent magnifications. We want to detect this cosmic magnification
effect in large samples of high-redshift galaxies selected from the Deep part
of the CFHTLS. Lyman-break galaxies (LBGs) at z=2.5-5, are used as a background
sample and are cross-correlated to foreground lens galaxies selected by
photo-z's. The signals of LBGs in different magnitude bins are compared to
predictions from WL theory. An optimally weighted correlation function is
estimated by taking into account the slope of external LBG luminosity
functions. For the first time, we detect cosmic magnification in a sample of
normal galaxies. These background sources are also the ones with the highest
redshifts so far used for WL measurements. The amplitude and angular dependence
of the cross-correlation functions agree well with theoretical expectations and
the lensing signal is detected with high significance. In particular, we detect
an anti-correlation between faint LBGs and foreground galaxies which cannot be
caused by redshift overlap. (abridged)
