MOND and the dynamics of NGC1052-DF2

TL;DR

This paper evaluates whether Modified Newtonian Dynamics (MOND) can explain the velocity dispersion of dwarf galaxy NGC1052-DF2, considering external and internal gravitational fields, and finds results consistent with observations.

Contribution

It provides a detailed analysis of MOND predictions for NGC1052-DF2, incorporating external field effects, and discusses observational and theoretical caveats affecting the interpretation.

Findings

MOND predicts a velocity dispersion of about 13.4 km/s for NGC1052-DF2.

Observed velocity dispersion is approximately 14.3 km/s, aligning with MOND predictions.

Further data analysis is needed to confirm if NGC1052-DF2 challenges or supports MOND.

Abstract

The dwarf galaxy NGC1052-DF2 has recently been identified as potentially lacking dark matter. If correct, this could be a challenge for MOND, which predicts that low surface brightness galaxies should evince large mass discrepancies. However, the correct prediction of MOND depends on both the internal field of the dwarf and the external field caused by its proximity to the giant elliptical NGC1052. Taking both into consideration under plausible assumptions, we find $\sigma_{\rm MOND} = 13.4^{+4.8}_{-3.7}\;\mathrm{km}\,\mathrm{s}^{-1}$. This is only marginally higher than the claimed 90\% upper limit on the velocity dispersion ($\sigma < 10.5\;\mathrm{km}\,\mathrm{s}^{-1}$), and compares well with the observed root mean square velocity dispersion ($\sigma = 14.3\;\mathrm{km}\,\mathrm{s}^{-1}$). We also discuss a few caveats on both the observational and theoretical side. On the theory side, the internal virialization time in this dwarf may be longer that the time scale of variation of the external field. On the observational side, the paucity of data and their large uncertainties call for further analysis of the velocity dispersion of NGC1052-DF2, to check whether it poses a challenge to MOND or is a success thereof.