Constraining galaxy properties with complete samples of lenses

¹ Leiden Observatory, Leiden University, P.O. Box 9513 2300 RA Leiden, The Netherlands
² Department of Astronomy, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
³ Shanghai Key Laboratory for Particle Physics and Cosmology, Shanghai Jiao Tong University Shanghai 200240, China,
⁴ Key Laboratory for Particle Physics, Astrophysics and Cosmology, Ministry of Education, Shanghai Jiao Tong University, Shanghai 200240, China

^⋆ Corresponding author; sonnenfeld@sjtu.edu.cn

Received: 24 June 2024
Accepted: 17 September 2024

Abstract

The statistics of Einstein radii for a sample of strong lenses can provide valuable constraints on the underlying mass distribution. The correct interpretation, however, relies critically on the modelling of the selection of the sample, which has proven to be a limiting factor. This may change thanks to upcoming uniform high-resolution imaging surveys that cover a large fraction of the sky because they can provide complete lens samples with well-understood selection criteria. To explore how the observed distribution of Einstein radii depends on the galaxy properties, we simulated a realistic complete sample of strong lenses, predicting a number density of lenses of about 2.5 deg⁻² for a Euclid-like setup. Such data can break the degeneracy between the stellar initial mass function and the inner slope of the density profile of dark matter, without having to rely on additional information from stellar dynamics. We find that a survey covering only 50 deg² can already provide tight constraints: assuming that the cosmology is known, the dark matter slope is recovered with an uncertainty of 3.5%, while the uncertainty in the ratio between the true stellar mass and that inferred from stellar population modelling is 10%. These findings highlight the potential of this method when applied to samples of lenses with well-understood selection functions.