Testing the MOND Paradigm of Modified Dynamics with Galaxy-Galaxy Gravitational Lensing

TL;DR

This paper tests the MOND paradigm against galaxy-galaxy gravitational lensing data, finding that MOND accurately predicts the observed lensing effects with baryonic matter alone, unlike Newtonian analysis which implies large unseen mass.

Contribution

It provides empirical validation of MOND's predictions for galaxy-galaxy lensing, extending tests of MOND to lower accelerations and a broader galaxy population.

Findings

MOND predicts a logarithmic potential consistent with lensing observations.

Baryonic mass explains lensing data without dark matter in MOND.

Newtonian analysis requires large unseen mass, contradicting baryonic matter estimates.

Abstract

MOND predicts that the asymptotic gravitational potential of an isolated, bounded (baryonic) mass, M, is phi(r)=(MGa0)^{1/2}ln(r); a0 is the MOND constant. Relativistic MOND theories predict that the lensing effects of M are dictated by phi(r) as general-relativity lensing is dictated by the Newtonian potential. Thus, MOND predicts that the asymptotic Newtonian potential deduced from galaxy-galaxy gravitational lensing will have: (1) a logarithmic r dependence, and (2) a normalization (parametrized standardly as 2s^2) that depends only on M: s=(MGa0/4)^{1/4}. I compare these predictions with recent results of galaxy-galaxy lensing, and find agreement on all counts. For the "blue"-lenses subsample ("spiral" galaxies) MOND reproduces the observations well with an r'-band M/L of 1-3 solar units, and for "red" lenses ("elliptical" galaxies) with M/L of 3-6 solar units, both consistent with baryons only. In contradistinction, Newtonian analysis requires, typically, M/L values of about 130 solar units, bespeaking a mass discrepancy of a factor of about 40. Compared with the staple, rotation-curve tests, MOND is here tested in a wider population of galaxies, through a different phenomenon, using relativistic test objects, and is probed to several-times-lower accelerations--as low as a few percent of a0.