Strong lensing selection effects

Abstract

Context. Strong lenses are a biased subset of the general population of galaxies. Aims. The goal of this work is to quantify how lens galaxies and lensed sources differ from their parent distribution, namely the strong lensing bias. Methods. We first studied how the strong lensing cross-section varies as a function of lens and source properties. Then, we simulated strong lensing surveys with data similar to that expected for Euclid and measured the strong lensing bias in different scenarios. We focused particularly on two quantities: the stellar population synthesis mismatch parameter, α sps , defined as the ratio between the true stellar mass of a galaxy and the stellar mass obtained from photometry, and the central dark matter mass at fixed stellar mass and size. Results. Strong lens galaxies are biased towards larger stellar masses, smaller half-mass radii and larger dark matter masses. The amplitude of the bias depends on the intrinsic scatter in the mass-related parameters of the galaxy population and on the completeness in Einstein radius of the lens sample. For values of the scatter that are consistent with observed scaling relations and a minimum detectable Einstein radius of 0.5 , the strong lensing bias in α sps is 10%, while that in the central dark matter mass is 5%. The bias has little dependence on the properties of the source population: samples of galaxy-galaxy lenses and galaxy-quasar lenses that probe the same Einstein radius distribution are biased in a very similar way. Quadruply imaged quasar lenses, however, are biased towards higher ellipticity galaxies. Conclusions. Given current uncertainties, strong lensing observations can be used directly to improve our current knowledge of the inner structure of galaxies, without the need to correct for selection effects.

Large data set of lensed quasars: higher accuracy on H0? The angular structures viewpoint

“…This result is true provided that the population is well represented by a 50-50 percentage of discy versus boxy galaxies, as measured by Mitsuda et al (2017) for massive elliptical galaxies, and by a distribution of strength of multipolar deviations similar to the one measured by Hao et al (2006). The upcoming time-delay cosmography in the big data era will benefit from studying selections effects in lenses (Sonnenfeld et al 2023).…”

Strong Lensing by Galaxies: Past Highlights, Current Status, and Future Prospects

“…As the statistical precision grows tighter with these future large samples, systematic effects such as the selection function will become increasingly important, if not already. Using simulation, Sonnenfeld et al (2023) show that strong lensing samples can be biased in the IMF mismatch parameter by ∼10% and in the dark matter inner slope by ∼5% (Fig. 4).…”

“…Thus, Rubin, Euclid, and Roman observatories will play key roles in providing those answers in the forthcoming era of big data. Sonnenfeld et al (2023): from left to right, stellar mass M , halo mass M halo , IMF mismatch α, and dark matter (DM) inner slope. The IMF mismatch parameter in strong lensing galaxies is biased by 10% from the parent population, and the dark matter inner slope is biased by 5%.…”

Galaxy and Mass Assembly (GAMA): Stellar-to-dynamical Mass Relation. I. Constraining the Precision of Stellar Mass Estimates

“…Strong gravitational lensing arguably provides the purest gravitational measure of stellar mass (e.g., Posacki et al 2015;Smith et al 2015;Sonnenfeld et al 2019). However, these lensing events are rare, and therefore such mass measurements are limited by small sample sizes, as well as complex and potentially significant selection effects (Sonnenfeld et al 2023).…”