Self-similar models for the mass profiles of early-type lens galaxies

D. Rusin, C. S. Kochanek, C. R. Keeton

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129 Scopus citations


We introduce a self-similar mass model for early-type galaxies and constrain it using the aperture mass-radius relations determined from the geometries of 22 gravitational lenses. The model consists of two components: a concentrated component, which traces the light distribution, and a more extended power-law component (ρ α r-n), which represents the dark matter. We find that lens galaxies have total mass profiles that are nearly isothermal, or slightly steeper, on the several-kiloparsec radial scale spanned by the lensed images. In the limit of a single-component, power-law radial profile, the model implies n = 2.07 ± 0.13, consistent with isothermal (n = 2). Models in which mass traces light are excluded at higher than 99% confidence. An n = 1 cusp (such as the Navarro-Frenk-White profile) requires a projected dark matter mass fraction of fcdm = 0.22 ± 0.10 inside two effective radii. These are the best statistical constraints yet obtained on the mass profiles of lenses and provide clear evidence for a small but nonzero dark matter mass fraction in the inner regions of early-type galaxies. In addition, we derive the first strong-lending constraint on the relation between the stellar mass-to-light ratio γ and galaxy luminosity L, γ α L0.14+0.16 -0.12, which is consistent with the relation suggested by the fundamental plane. Finally, we apply our self-similar mass models to current problems regarding the interpretation of time delays and flux ratio anomalies in gravitational lens systems.

Original languageEnglish (US)
Pages (from-to)29-42
Number of pages14
JournalAstrophysical Journal
Issue number1 I
StatePublished - Sep 20 2003

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Galaxies: Elliptical and lenticular, cD
  • Galaxies: Structure
  • Gravitational lensing


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