Golden gravitational lensing systems from the Sloan Lens ACS Survey. II.
  SDSS J1430+4105: A precise inner total mass profile from lensing alone
  We study the SLACS strong lensing system SDSSJ1430+4105 at z=0.285. The
lensed source (z=0.575) of this system has a complex morphology with several
subcomponents. Its subcomponents span a radial range from 4 to 10kpc in the
lens plane. Therefore we can constrain the slope of the total projected mass
profile around the Einstein radius (R_E) from lensing alone. We measure a
density profile that is slightly but not significantly shallower than
isothermal at R_E. We decompose the mass of the lensing galaxy into a de
Vaucouleurs (deV) component to trace the stars and an additional dark
component. The spread of multiple image components over a large radial range
also allows us to determine the amplitude of the deV and dark matter components
separately. We get a mass to light ratio of M_deV/L_B~5.5\pm1.5M/L_sun,B and a
dark matter fraction within R_E of ~20 to 40%. Modelling the star formation
history assuming composite stellar populations at solar metallicity to the
galaxy's photometry yields a mass to light ratio of
M_star,salp/L_B~4.0_{-1.3}^{+0.6}M/L_sun,B and
M_star,chab/L_B~2.3_{-0.8}^{+0.3}M/L_sun,B for Salpeter and Chabrier IMFs,
respectively. Hence, the mass to light ratio derived from lensing is more
Salpeter-like, in agreement with results for massive Coma galaxies and other
nearby massive early type galaxies. We examine the consequences of the galaxy
group in which the lensing galaxy is embedded, showing that it has little
influence on the mass to light ratio obtained for the deV component of the
lensing galaxy. Finally, we decompose the projected, azimuthally averaged 2D
density distribution of the deV and dark matter component of the lensing signal
into spherically averaged 3D density profiles. We can show that the 3D dark and
luminous matter density within R_E~0.6R_eff of this SLACS galaxy is similar to
the values of Coma galaxies with the same velocity dispersions.
