A Novel Test for MOND: Gravitational Lensing by Disc Galaxies

TL;DR

This paper explores gravitational lensing by disc galaxies within the MOND framework, predicting distinctive effects and increased lens counts that could help distinguish MOND from dark matter in upcoming surveys.

Contribution

It introduces a novel method to analyze disc galaxy lensing in MOND using equivalent Newtonian systems and predicts observable differences from dark matter models.

Findings

MOND predicts dominant effects in lensing by disc galaxies.

A substantial increase in lens count is expected under MOND.

Correlations between galaxy parameters and lensing cross section are identified.

Abstract

Disc galaxies represent a promising laboratory for the study of gravitational physics, including alternatives to dark matter, owing to the possibility of coupling rotation curves' dynamical data with strong gravitational lensing observations. In particular, Euclid, DES and LSST are predicted to observe hundreds of thousands of gravitational lenses. Here, we investigate disc galaxy strong gravitational lensing in the MOND framework. We employ the concept of equivalent Newtonian systems within the quasi-linear MOND formulation to make use of the standard lensing formalism. We derive the phantom dark matter distribution predicted for realistic disc galaxy models and study the impact of morphological and mass parameters on the expected lensing. We find purely MONDian effects dominate the lensing and generate non-trivial correlations between the lens parameters and the lensing cross section. Moreover, we show that the standard realisation of MOND predicts a substantial increase in the number count of disc galaxy lenses compared to the dark matter-driven predictions, making it distinguishable from the latter in upcoming surveys. Finally, we argue that disc galaxy gravitational lensing, coupled to additional astronomical observations, can be used to constrain the interpolating function of MOND.