The Sloan Lens ACS Survey. III. The structure and formation of early-type galaxies and their evolution since z approximate to 1

Koopmans, L. V. E., Treu, T., Bolton, A. S., Burles, S. & Moustakas, L. A., 1-Oct-2006, In : Astrophysical Journal. 649, 2, p. 599-615 17 p.

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We present a joint gravitational lensing and stellar-dynamical analysis of 15 massive field early-type galaxies selected from the Sloan Lens ACS (SLACS) Survey. The following numerical results are found: (1) A joint likelihood gives an average logarithmic density slope for the total mass density of = 2.01(-0.03)(+0.02) (68% CL; rho(tot) proportional to r(-gamma')) <R-Einst > = 4.2 +/- 0.4 kpc (rms of 1.6 kpc) for isotropic models. The inferred intrinsic rms spread in logarithmic density slopes is sigma(gamma') = 0.12. (2) The average position-angle difference between the light distribution and the total mass distribution is found to be = 0 degrees +/- 3 degrees (rms of 10 degrees), setting an upper limit of less than or similar to 0.035 on the average external shear. The total mass has an average ellipticity <q(SIE)> = 0.78 +/- 0.03 (rms of 0.12), which correlates extremely well with the stellar ellipticity, q(*), resulting in <q(SIE)/q(*)> = 0.99 +/- 0.03 (rms of 0.11) for sigma greater than or similar to 225 km s(-1) omitting three S0 lens galaxies. (3) The average projected dark matter mass fraction is inferred to be <f(DM)> = 0.25 +/- 0.06 (rms of 0.22) inside <R-Einst >, using the stellar mass-to-light ratios derived from the fundamental plane as priors. (4) Combined with results from the Lenses Structure and Dynamics (LSD) Survey at z greater than or similar to 0.3, we find no significant evolution of the total density slope inside one effective radius for galaxies with sigma(ap) >= 200 km s(-1): a linear fit gives alpha(gamma') equivalent to d / dz = 0.23 +/- 0.16 (1 sigma) for the range z = 0.08-1.01. The small scatter and absence of significant evolution in the inner density slopes suggest a collisional scenario in which gas and dark matter strongly couple during galaxy formation, leading to a total mass distribution that rapidly converges to dynamical isothermality.

Original languageEnglish
Pages (from-to)599-615
Number of pages17
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 1-Oct-2006


  • galaxies : elliptical and lenticular, cD, galaxies : evolution, galaxies : formation, galaxies : structure, gravitational lensing, COLD DARK-MATTER, DIGITAL SKY SURVEY, HIGH-REDSHIFT SUPERNOVAE, FIELD E/S0 GALAXIES, GROTH STRIP SURVEY, GRAVITATIONAL LENS, ELLIPTIC GALAXIES, FUNDAMENTAL PLANE, VIOLENT RELAXATION, INTERNAL STRUCTURE

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