• A
  • A
  • A
  • ABC
  • ABC
  • ABC
  • А
  • А
  • А
  • А
  • А
Regular version of the site

Article

Mass density slope of elliptical galaxies from strong lensing and resolved stellar kinematics

Monthly Notices of the Royal Astronomical Society. 2018. Vol. 475. No. 2. P. 2403-2414.
Lyskova N., Churazov E., Naab T.

We discuss constraints on the mass density distribution (parametrized as ρ ∝ r−γ) in early-type galaxies provided by strong lensing and stellar kinematics data. The constraints come from mass measurements at two ‘pinch’ radii. One ‘pinch’ radius r1 = 2.2REinst is defined such that the Einstein (i.e. aperture) mass can be converted into the spherical mass almost independently of the mass-model. Another ‘pinch’ radius r2 = Ropt is chosen so that the dynamical mass, derived from the line-of-sight velocity dispersion, is least sensitive to the anisotropy of stellar orbits. We verified the performance of this approach on a sample of simulated elliptical galaxies and on a sample of 15 SLACS lens galaxies at 0.01 ≤ z ≤ 0.35, which have already been analysed in Barnabè et al. by the self-consistent joint lensing and kinematic code. For massive simulated galaxies, the density slope γ is recovered with an accuracy of ∼13 per cent, unless r1 and r2 happen to be close to each other. For SLACS galaxies, we found good overall agreement with the results of Barnabè et al. with a sample-averaged slope γ = 2.1 ± 0.05. Although the two-pinch-radii approach has larger statistical uncertainties, it is much simpler and uses only few arithmetic operations with directly observable quantities.