We present the results of a strong-lensing analysis of a complete sample of
12 very luminous X-ray clusters at z>0.5 using HST/ACS images. Our modelling
technique has uncovered some of the largest known critical curves outlined by
many accurately-predicted sets of multiple images. The distribution of Einstein
radii has a median value of \simeq28\arcsec (for a source redshift of
zs∼2), twice as large as other lower-z samples, and extends to
55\arcsec for MACS J0717.5+3745, with an impressive enclosed Einstein mass of
7.4×1014M⊙. We find that 9 clusters cover a very large area
(>2.5 \sq \arcmin) of high magnification (μ>×10) for a source
redshift of zs∼8, providing primary targets for accessing the first
stars and galaxies. We compare our results with theoretical predictions of the
standard ΛCDM model which we show systematically fall short of our
measured Einstein radii by a factor of ≃1.4, after accounting for the
effect of lensing projection. Nevertheless, a revised analysis once arc
redshifts become available, and similar analyses of larger samples, are needed
in order to establish more precisely the level of discrepancy with ΛCDM
predictions.Comment: Accepted for publication in MNRAS, 19 pages, 35 figures, 2 tables. V2
includes several changes, mainly additional discussion of the results. A
higher resolution version is available at
ftp://wise-ftp.tau.ac.il/pub/adiz/macs1