The relation between stellar mass and weak lensing signal around galaxies: Implications for MOND

TL;DR

This study measures weak lensing signals around galaxies to test gravity theories, finding results inconsistent with MOND and supporting the presence of dark matter.

Contribution

It provides the first detailed measurement of lensing amplitude versus stellar mass that challenges MOND predictions and supports dark matter.

Findings

Lensing amplitude follows a power law with slope 0.74.

Results are inconsistent with MOND's predicted slope of 0.5.

Dark matter is necessary for luminous galaxies, ruling out gas or neutrino halos as alternatives.

Abstract

We study the amplitude of the weak gravitational lensing signal as a function of stellar mass around a sample of relatively isolated galaxies. This selection of lenses simplifies the interpretation of the observations, which consist of data from the Red- sequence Cluster Survey and the Sloan Digital Sky Survey. We find that the amplitude of the lensing signal as a function of stellar mass is well described by a power law with a best fit slope \alpha= 0.74 \pm 0.08. This result is inconsistent with Modified Newtonian Dynamics, which predicts \alpha = 0.5 (we find \alpha > 0.5 with 99.7% confidence). As a related test, we determine the MOND mass-to-light ratio as a function of luminosity. Our results require dark matter for the most luminous galaxies (L >=10^11 L_sun). We rule out an extended halo of gas or active neutrinos as a way of reconciling our findings with MOND. Although we focus on a single alternative gravity model, we note that our results provide an important test for any alternative theory of gravity.