Extensive light profile fitting of galaxy-scale strong lenses
  We investigate the merits of a massive forward modeling of ground-based
optical imaging as a diagnostic for the strong lensing nature of Early-Type
Galaxies, in the light of which blurred and faint Einstein rings can hide. We
simulate several thousand mock strong lenses under ground- and space-based
conditions as arising from the deflection of an exponential disk by a
foreground de Vaucouleurs light profile whose lensing potential is described by
a Singular Isothermal Ellipsoid. We then fit for the lensed light distribution
with sl_fit after having subtracted the foreground light emission off (ideal
case) and also after having fitted the deflector's light with galfit. By
setting thresholds in the output parameter space, we can decide the
lens/not-a-lens status of each system. We finally apply our strategy to a
sample of 517 lens candidates present in the CFHTLS data to test the
consistency of our selection approach. The efficiency of the fast modeling
method at recovering the main lens parameters like Einstein radius, total
magnification or total lensed flux, is quite comparable under CFHT and HST
conditions when the deflector is perfectly subtracted off (only possible in
simulations), fostering a sharp distinction between the good and the bad
candidates. Conversely, for a more realistic subtraction, a substantial
fraction of the lensed light is absorbed into the deflector's model, which
biases the subsequent fitting of the rings and then disturbs the selection
process. We quantify completeness and purity of the lens finding method in both
cases. This suggests that the main limitation currently resides in the
subtraction of the foreground light. Provided further enhancement of the
latter, the direct forward modeling of large numbers of galaxy-galaxy strong
lenses thus appears tractable and could constitute a competitive lens finder in
the next generation of wide-field imaging surveys.
