The necessity of dark matter in MOND within galactic scales

TL;DR

This study tests MOND on galactic scales using gravitational lensing data and finds that dark matter is necessary even within MOND, challenging its ability to fully explain galactic phenomena without additional components.

Contribution

The paper provides empirical evidence that dark matter is required in MOND models at galactic scales, based on gravitational lensing observations of early-type galaxies.

Findings

Dark matter is needed within MOND at galactic scales.

A 2 eV neutrino cannot account for the excess mass.

Dark matter detected in regions with higher acceleration than MOND's characteristic scale.

Abstract

To further test MOdified Newtonian Dynamics (MOND) on galactic scales -- originally proposed to explain the rotation curves of disk galaxies without dark matter -- we study a sample of six strong gravitational lensing early-type galaxies from the CASTLES database. To determine whether dark matter is present in these galaxies, we compare the total mass (from lensing) with the stellar mass content (from a comparison of photometry and stellar population synthesis). We find that strong gravitational lensing on galactic scales requires a significant amount of dark matter, even within MOND. On such scales a 2 eV neutrino cannot explain this excess matter -- in contrast with recent claims to explain the lensing data of the bullet cluster. The presence of dark matter is detected in regions with a higher acceleration than the characteristic MONDian scale of $\sim 10^{-10}$m/s$^2$. This is a serious challenge to MOND unless the proper treatment of lensing is qualitatively different (possibly to be developed within a consistent theory such as TeVeS).