Radial density profiles of time-delay lensing galaxies

J. I. Read, P. Saha, A. V. MacCiò

Research output: Contribution to journalArticlepeer-review


We present nonparametric radial mass profiles for 10 QSO strong-lensing galaxies. Five of the galaxies have profiles close to ρ(r) ∝ r -2, while the rest are closer to r-1, consistent with an NFW profile. The former are all relatively isolated early types and dominated by their stellar light. The latter-although the modeling code did not know this-are either in clusters, or have very high mass-to-light ratios, suggesting dark matter-dominant lenses (one is actually a pair of merging galaxies). The same models give H0-1 = 15.2-1.7+2.5 Gyr (H0 = 64-8+9 km s-1 Mpc -1 ), consistent with a previous determination. When tested on simulated lenses taken from a cosmological hydrodynamical simulation, our modeling pipeline recovers both H0 and ρ(r) within estimated uncertainties. Our result is contrary to some recent claims that lensing time delays imply either a low H0 or galaxy profiles much steeper than r-2. We diagnose these claims as resulting from an invalid modeling approximation: that small deviations from a power-law profile have a small effect on lensing time delays. In fact, as we show using both perturbation theory and numerical computation from a galaxy formation simulation, a first-order perturbation of an isothermal lens can produce a zeroth-order change in the time delays.

Original languageEnglish (US)
Pages (from-to)645-654
Number of pages10
JournalAstrophysical Journal
Issue number2 I
StatePublished - 2007


  • Galaxies: halos
  • Gravitational lensing

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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