Hubble Frontier Fields : A High Precision Strong Lensing Analysis of Galaxy Cluster MACSJ0416.1-2403 using ~200 Multiple Images

International audienceWe present a high-precision mass model of the galaxy cluster MACSJ0416.1-2403, based on a strong-gravitational-lensing analysis of the recently acquired Hubble Space Telescope Frontier Fields (HFF) imaging data. Taking advantage of the unprecedented depth provided by HST/ACS observations in three passbands, we identify 51 new multiply imaged galaxies, quadrupling the previous census and bringing the grand total to 68, comprising 194 individual lensed images. Having selected a subset of the 57 most securely identified multiply imaged galaxies, we use the Lenstool software package to constrain a lens model comprised of two cluster-scale dark-matter halos and 98 galaxy-scale halos. Our best-fit model predicts image positions with an $RMS$ error of 0.68'', which constitutes an improvement of almost a factor of two over previous, pre-HFF models of this cluster. We find the total projected mass inside a 200~kpc aperture to be $(1.60\pm0.01)\times 10^{14}\ M_\odot$, a measurement that offers a three-fold improvement in precision, reaching the percent level for the first time in any cluster. Finally, we quantify the increase in precision of the derived gravitational magnification of high-redshift galaxies and find an improvement by a factor of $\sim$2.5 in the statistical uncertainty. Our findings impressively confirm that HFF imaging has indeed opened the domain of high-precision mass measurements for massive clusters of galaxies