RESOLVING THE BARYON-FRACTION PROFILE IN LENSING GALAXIES

The study of the distribution of baryonic matter within dark halos enriches our understanding of galaxy formation. We show the radial dependence of stellar baryon-fraction curves derived for 21 lensing galaxies from the CfA-Arizona Space Telescope LEns Survey (CASTLES) by means of stellar population synthesis and pixel-based mass reconstruction. The sample covers a stellar mass range of M-s similar or equal to 2 x 10(9)-3 x 10(11) M-circle dot (solar masses) which corresponds to a total enclosed mass range of M-L similar or equal to 7 x 10(9)-3 x 10(12) M-circle dot on radial scales from 0.25 R-e to 5 R-e (effective radii). By examining the M-s and M-L dependence on radial distance to the center of each galaxy, we find that there are pairs of lenses on small to intermediate mass scales which approach at large radii the same values for their enclosed total mass but exhibit very different stellar masses and stellar baryon fractions. This peculiar behavior 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 2.5R(e). At 3R(e) most of the stellar component is enclosed. We find evidence for a stellar baryon fraction steadily declining over the full mass range. Furthermore, we shed light on the Fundamental Plane puzzle by showing that the slope of the M-L(< R)-to-M-s (