* Astronomy

Title: Resolving the baryon-fraction profile in lensing galaxies
Authors: Dominik Leier, Ignacio Ferreras, Prasenjit Saha, Emilio E. Falco

We present a study of the radial dependence of stellar mass or baryon fraction for 21 lensing galaxies from the CfA-Arizona Space Telescope LEns (CASTLE) survey by stellar population synthesis and pixel-based mass reconstruction. The sample covers a stellar mass (Ms) range from 2x10^9 to 3x10^11 Msol which corresponds to a total lensing mass (ML) range of 7x10^9 - 3x10^12 Msol on scales from 0.25 to 5 Re (effective radii). Examining the Ms and ML dependence on radius, we find that there are pairs of lenses on small to intermediate mass scales with similar enclosed mass at large radii but very different stellar masses. This peculiar behaviour subsides for the most massive lensing galaxies. All the baryon fraction profiles show that the dark matter halo overtakes the stellar content between 1.5 and 2.5 Re. At 3 Re most of the stellar component is enclosed. We find evidence for a stellar baryon fraction steadily declining over the full mass range. We find that the slope of the ML(<R)-to-Ms(<R) relation approaches the mass-to-light relation of recent Fundamental Plane studies at large radii. We also introduce new concentration indices for stellar and total mass profiles, and find that the value c=2.6 which separates early-type galaxies from late-type galaxies also holds for stellar mass concentrations. In particular, less massive dark matter halos turn out to be influenced by the distribution of stellar matter on resolved scales below 10 kpc. The ongoing study of resolved baryon fraction profiles will make it possible to evaluate the validity of star formation models as well as adiabatic contraction prescriptions commonly used in simulations.

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