MUSE observations of the lensing cluster Abell 1689
  We present the results obtained with MUSE on the core of the lensing cluster
A1689. Integral-field observations with MUSE provide a unique view of the
central region, allowing us to conduct a complete census on both cluster
galaxies and lensed background sources, identified based on their spectral
features without preselection. We investigate the multiple-image configuration
for all known sources in the field. Previous to our survey, 28 different lensed
galaxies displaying 46 multiple images were known in the MUSE field of view,
most of them based on photometric redshifts and lensing considerations. Among
them, we spectroscopically confirm 12 images based on their emission-lines,
corresponding to 7 different lensed galaxies between z = 0.95 and 5.0. In
addition, 14 new galaxies have been spectroscopically identified in this area,
with redshifts ranging between 0.8 and 6.2. All background sources within the
MUSE field of view correspond to multiple-imaged systems lensed by A1689. 17
sources in total are found at z > 3 based on their Lyman-alpha emission, with
Lyman-alpha luminosities ranging between 40.5 < log(Ly{\alpha}) < 42.5 after
correction for magnification. This sample is particularly sensitive to the
slope of the LF toward the faintest-end. The density of sources obtained in
this survey is consistent with a steep value of {\alpha} < -1.5, although this
result still needs further investigation. These results illustrate the
efficiency of MUSE in the characterization of lensing clusters on one hand, and
the study of faint and distant populations of galaxies on the other hand. In
particular, our current survey of lensing clusters should provide a unique
census of sources responsible for the reionization in a representative volume
at z ~ 4-7.
