Lensing and Dynamics in Two Simple Steps

Abstract

We present a ready-to-use method to constrain the density distribution in early-type galaxy lenses. Assuming a power-law density profile, then joint use of the virial theorem and the lens equation yields simple formulae for the power-law index (or logarithmic density gradient). Any dependence on orbital anisotropy can be tightly constrained or even erased completely. Our results rely just on surface brightnesses and line-of-sight kinematics, making deprojection unnecessary. We revisit three systems that have already been examined in the literature (the Cosmic Horseshoe, the Jackpot and B1608+656) and provide our estimates. Finally, we show that the method yields a good approximation for the density profile even when the true profile is a broken power-law, albeit with a mild bias towards isothermality.

5 pages, 3 figures, MNRAS, submitted

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• The Sloan Lens ACS Survey. V. The Full ACS Strong-Lens Sample
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• Improving time-delay cosmography with spatially resolved kinematics
• Dynamical Models of Elliptical Galaxies -- II. M87 and its Globular Clusters
• Dynamical Models of Elliptical Galaxies -- I. Simple Methods
• CLASH: Extending galaxy strong lensing to small physical scales with distant sources highly-magnified by galaxy cluster members
• Mass density slope of elliptical galaxies from strong lensing and resolved stellar kinematics
• Zooming into the Cosmic Horseshoe: new insights on the lens profile and the source shape
• Measuring the total and baryonic mass profiles of the very massive CASSOWARY 31 strong lens. A fossil system at z ~ 0.7?
• Minimal lensing solutions in the singular perturbative approach