Current velocity data on dwarf galaxy NGC1052-DF2 do not constrain it to lack dark matter

TL;DR

This study shows that current velocity data for dwarf galaxy NGC1052-DF2 do not definitively indicate a lack of dark matter, highlighting the importance of careful statistical analysis and accounting for uncertainties in small data sets.

Contribution

The paper demonstrates that velocity dispersion measurements are weakly constrained and emphasizes the need for rigorous statistical methods in dynamical mass estimation of dwarf galaxies.

Findings

Velocity dispersion is consistent with a normal range, not necessarily indicating absence of dark matter.

Models including field contaminants do not significantly improve constraints.

Weak upper limits on mass-to-light ratio are consistent with many Local Group dwarf galaxies.

Abstract

It was recently proposed that the globular cluster system of the very low surface-brightness galaxy NGC1052-DF2 is dynamically very cold, leading to the conclusion that this dwarf galaxy has little or no dark matter. Here, we show that a robust statistical measure of the velocity dispersion of the tracer globular clusters implies a mundane velocity dispersion and a poorly constrained mass-to-light ratio. Models that include the possibility that some of the tracers are field contaminants do not yield a more constraining inference. We derive only a weak constraint on the mass-to-light ratio of the system within the half-light radius (M/L_V<6.7 at the 90% confidence level) or within the radius of the furthest tracer (M/L_V<8.1 at the 90% confidence level). This limit may imply a mass-to-light ratio on the low end for a dwarf galaxy but many Local Group dwarf galaxies fall well within this contraint. With this study, we emphasize the need to reliably account for measurement uncertainties and to stay as close as possible to the data when determining dynamical masses from very small data sets of tracers.