The Globular Cluster Population of NGC 1052-DF2: Evidence for Rotation

TL;DR

This study discovers rotation in the globular cluster system of galaxy NGC 1052-DF2, suggesting that its mass and dark matter content may be underestimated if rotation is ignored, challenging previous assumptions.

Contribution

It provides the first evidence of globular cluster rotation in NGC 1052-DF2, impacting mass estimates and dark matter inferences for this galaxy.

Findings

Detected globular cluster rotation with ~12.44 km/s amplitude.

Rotation signature is approximately perpendicular to stellar rotation.

Mass-to-light ratio can exceed 10 with moderate inclination.

Abstract

Based upon the kinematics of ten globular clusters, it has recently been claimed that the ultra-diffuse galaxy, NCD 1052-DF2, lacks a significant quantity of dark matter. Dynamical analyses have generally assumed that this galaxy is pressure supported, with the relatively small velocity dispersion of the globular cluster population indicating the deficit of dark matter. However, the presence of a significant rotation of the globular cluster population could substantially modify this conclusion. Here we present the discovery of such a signature of rotation in the kinematics of NGC 1052-DF2's globular clusters, with a velocity amplitude of $\sim12.44^{+4.40}_{-5.16}$ km/s, which, through Bayesian model comparison, represents a marginally better fit to the available kinematic data; note that this rotation is distinct from, and approximately perpendicular to, the recently identified rotation of the stellar component of NGC 1052-DF2. Assuming this truly represents an underlying rotation, it is shown that the determined mass depends upon the inclination of the rotational component and, with a moderate inclination, the resultant mass to light ratio can exceed $M/L\sim10$.