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We present free-form gravitational lensing models derived with the WSLAP+ code for the six Hubble Frontier Fields clusters using the latest data available from the Frontier Fields Lensing Models v.4 collaboration. We present magnification maps in the lens plane and caustic maps in the source plane. From these maps, we derive the probability of magnification using two different, but related, methods. We confirm MACS 0717 as the cluster with the most complex structure, and having the largest lensing efficiency and Einstein radius.When comparing these results with the ones obtained by previous observations of these clusters, we obtain an increase in the lensing efficiency between 1.4 and 2.3.We also find a good correlation with a relatively small dispersion between the lensing efficiency and Einstein radius as a function of the source redshift (z). Finally, we estimate the lensing effects produced by the six Hubble Frontier Fields clusters on the luminosity function of galaxies at high redshift (z = 9) for standard luminosity functions and an alternative luminosity function based on predictions from wave dark matter (φDM) models., JV-F and GMB acknowledge support from the Space Telescope Science Institute (contract number 49726). JMD acknowledges the support of projects AYA2015-64508-P funded by the Ministerio de Economia y Competitividad (MINECO/FEDER, UE). JV-F and JMD acknowledge the hospitality of the University of Pennsylvania.

We present Hubble Space Telescope/Wide Field Camera 3 narrow-band imaging of the Hα emission in a sample of eight gravitationally lensed galaxies at z = 1-1.5. The magnification caused by the foreground clusters enables us to obtain a median source plane spatial resolution of 360pc, as well as providing magnifications in flux ranging from ~10× to ~50×. This enables us to identify resolved star-forming Hii regions at this epoch and therefore study their Hα luminosity distributions for comparisons with equivalent samples at z ~ 2 and in the local Universe. We find evolution in the both luminosity and surface brightness of Hii regions with redshift. The distribution of clump properties can be quantified with an Hii region luminosity function, which can be fit by a power law with an exponential break at some cut-off, and we find that the cut-off evolves with redshift. We therefore conclude that 'clumpy' galaxies are seen at high redshift because of the evolution of the cut-off mass; the galaxies themselves follow similar scaling relations to those at z = 0, but their Hii regions are larger and brighter and thus appear as clumps which dominate the morphology of the galaxy. A simple theoretical argument based on gas collapsing on scales of the Jeans mass in a marginally unstable disc shows that the clumpy morphologies of high-z galaxies are driven by the competing effects of higher gas fractions causing perturbations on larger scales, partially compensated by higher epicyclic frequencies which stabilize the disc., RCL acknowledges a studentship from STFC, RGB and IS are supported by STFC and IS further acknowledges a Leverhulme Senior Fellowship. AMS acknowledges an STFC Advanced Fellowship, and JR is supported by the Marie Curie Career Integration Grant 294074. HE gratefully acknowledges financial support from STScI grants GO-09722, GO-10491, GO10875 and GO-12166. This work is based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for Program number 12197 and Program number 11678 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555