First test of Verlinde's theory of Emergent Gravity using Weak Gravitational Lensing measurements

TL;DR

This study tests Verlinde's Emergent Gravity theory against weak gravitational lensing data from a large galaxy survey, finding good agreement and providing initial observational support for the theory.

Contribution

It presents the first empirical test of Emergent Gravity using weak lensing measurements, comparing predictions with observations across multiple stellar mass bins.

Findings

EG predictions match observed lensing profiles in four stellar mass bins

No free parameters were needed for the EG predictions

Results support the viability of EG as an alternative to dark matter

Abstract

Verlinde (2016) proposed that the observed excess gravity in galaxies and clusters is the consequence of Emergent Gravity (EG). In this theory the standard gravitational laws are modified on galactic and larger scales due to the displacement of dark energy by baryonic matter. EG gives an estimate of the excess gravity (described as an apparent dark matter density) in terms of the baryonic mass distribution and the Hubble parameter. In this work we present the first test of EG using weak gravitational lensing, within the regime of validity of the current model. Although there is no direct description of lensing and cosmology in EG yet, we can make a reasonable estimate of the expected lensing signal of low redshift galaxies by assuming a background LambdaCDM cosmology. We measure the (apparent) average surface mass density profiles of 33,613 isolated central galaxies, and compare them to those predicted by EG based on the galaxies' baryonic masses. To this end we employ the ~180 square degrees overlap of the Kilo-Degree Survey (KiDS) with the spectroscopic Galaxy And Mass Assembly (GAMA) survey. We find that the prediction from EG, despite requiring no free parameters, is in good agreement with the observed galaxy-galaxy lensing profiles in four different stellar mass bins. Although this performance is remarkable, this study is only a first step. Further advancements on both the theoretical framework and observational tests of EG are needed before it can be considered a fully developed and solidly tested theory.