Effects of galaxy-halo alignment and adiabatic contraction on gravitational lens statistics

TL;DR

This paper investigates how galaxy-halo alignment and adiabatic contraction influence strong gravitational lensing statistics, highlighting the importance of these factors for interpreting lensing data and future surveys.

Contribution

It provides a detailed analysis of the effects of galaxy-halo shape alignment and adiabatic contraction on lensing image configurations and probabilities, using triaxial CDM halo models.

Findings

Adiabatic contraction increases total lensing probability.

Naked cusp configurations dominate at small separations without adiabatic contraction.

Image multiplicities are sensitive to galaxy-halo shape alignment.

Abstract

We study the strong gravitational lens statistics of triaxial cold dark matter (CDM) halos occupied by central early-type galaxies. We calculate the image separation distribution for double, cusp and quad configurations. The ratios of image multiplicities at large separations are consistent with the triaxial NFW model, and at small separations are consistent with the singular isothermal ellipsoid (SIE) model. At all separations, the total lensing probability is enhanced by adiabatic contraction. If no adiabatic contraction is assumed, naked cusp configurations become dominant at approximately 2.5'', which is inconsistent with the data. We also show that at small-to-moderate separations, the image multiplicities depend sensitively on the alignment of the shapes of the luminous and dark matter projected density profiles. In constrast to other properties that affect these ratios, the degree of alignment does not have a significant effect on the total lensing probability. These correlations may therefore be constrained by comparing the theoretical image separation distribution to a sufficiently large lens sample from future wide and deep sky surveys such as Pan-Starrs, LSST and JDEM. Understanding the correlations in the shapes of galaxies and their dark matter halo is important for future weak lensing surveys.