The first JWST data on the massive colliding cluster El Gordo confirm 23
known families of multiply lensed images and identify 8 new members of these
families. Based on these families, which have been confirmed spectroscopically
by MUSE, we derived an initial lens model. This model guided the identification
of 37 additional families of multiply lensed galaxies, among which 28 are
entirely new systems, and 9 were previously known. The initial lens model
determined geometric redshifts for the 37 new systems. The geometric redshifts
agree reasonably well with spectroscopic or photometric redshifts when those
are available. The geometric redshifts enable two additional models that
include all 60 families of multiply lensed galaxies spanning a redshift range
2<z<6. The derived dark-matter distribution confirms the double-peak
configuration of mass found by earlier work with the southern and northern
clumps having similar masses. We confirm that El Gordo is the most massive
known cluster at z>0.8 and has an estimated virial mass close the maximum
mass allowed by standard cosmological models. The JWST images also reveal the
presence of small-mass perturbers that produce small lensing distortions. The
smallest of these is consistent with being a dwarf galaxy at z=0.87 and has
an estimated mass of 3.8×109~\Msol, making it the smallest substructure
found at z>0.5. The JWST images also show several candidate caustic-crossing
events. One of them is detected at high significance at the expected position
of the critical curve and is likely a red supergiant star at z=2.1878. This
would be the first red supergiant found at cosmological distances. The cluster
lensing should magnify background objects at z>6, making more of them visible
than in blank fields of similar size, but there appears to be a deficiency of
such objects.Comment: 27 pages, 21 figure