  We present the first results of a spectroscopic survey of faint lensed
galaxie s in the core of the galaxy cluster AC114 (z=0.312) obtained from
observations w ith the FORS1 spectrograph mounted on the VLT-Antu. The galaxies
were chose n in areas close to the high-z critical lines predicted by the
gravitational lens model of Natarajan et al (NKSE, 1998) for this cluster,
according to both lensing and photometric redshift criteria. All the target
galaxies are found to correspond to background galaxies with redshifts values
in the [0.7, 3.5] interval. Our spectroscopic observations confirm the
predicted lensing redshifts for 3 of the multiple-image galaxies, and together
with predictions of the NKSE model led to the discovery of a new 5-image
configuration at redshift z=3.347. A revised NKSE model, compatible with the
redshift of this new multiple-image system, was generated and employed to
calculate the gravitational amplifications of all the observed galaxies. The
galaxies corresponding to the multiple-image systems are found to be
intrinsically fainter, between 0.5 and 1.5 magnitudes, than the limiting
magnitudes of existing blank field studies. When all the observed background
galaxies are considered, the resulting intrinsic absolute magnitudes range from
M_B~-22 to -19. Therefore, a large gain in sensitivity towards low luminosity
high-z objects can actually be obtained, in agreement with theoretical
expectations. This method can be used advantageously to probe the high redshift
Universe and, in particular, its application to an ensemble of massive cluster
cores could constraint the faint end of luminosity function of high redshift
galaxies.
