Direct measurement of lensing amplification in Abell S1063 using a
  strongly lensed high redshift HII Galaxy
  ID11 is an actively star forming extremely compact galaxy and Ly alpha
emitter at z=3.117 that is gravitationally magnified by a factor of ~17 by the
cluster of galaxies Hubble Frontier Fields AS1063. Its observed properties
resemble those of low luminosity HII galaxies or Giant HII regions like
30-Doradus in the LMC.
  Using the tight correlation correlation between the Balmer-line luminosities
and the width of the emission lines (typically L(Hbeta)-sigma(Hbeta)) valid for
HII galaxies and Giant HII regions to estimate its total luminosity, we are
able to measure the lensing amplification of ID11. We obtain an amplification
of 23 +- 11 similar within errors to the value of ~17 estimated or predicted by
the best lensing models of the massive cluster Abell S1063.
  We also compiled from the literature luminosities and velocity dispersions
for a set of lensed compact starforming regions. There is more scatter in the
L-sigma correlation for these lensed systems but on the whole the results tend
to support the lensing models estimates of the magnification.
  Our result indicates that the amplification can be independently measured
using the L-sigma relation in lensed Giant HII regions or HII galaxies. It also
supports the suggestion, even if lensing model dependent, that the L-sigma
relation is valid for low luminosity high-z objects. Ad-hoc observations of
lensed starforming systems are required to accurately determine the lensing
amplification.
