The ultra-diffuse galaxy NGC 1052-DF2 with MUSE: I. Kinematics of the stellar body

TL;DR

This study uses MUSE spectroscopy to analyze the stellar kinematics of the ultra-diffuse galaxy NGC 1052-DF2, providing insights into its velocity field, globular cluster membership, and mass estimates, challenging previous notions of its dark matter content.

Contribution

First spectroscopic analysis of NGC 1052-DF2's stellar body with detailed kinematic measurements, confirming globular cluster memberships and estimating the galaxy's velocity dispersion and mass.

Findings

Detected a weak velocity gradient indicating prolate-like rotation.

Measured a stellar velocity dispersion upper limit of 21 km/s within one effective radius.

Confirmed additional globular cluster memberships, increasing the specific frequency.

Abstract

The so-called ultra-diffuse galaxy NGC~1052-DF2 was announced to be a galaxy lacking dark matter based on a spectroscopic study of its constituent globular clusters. Here we present the first spectroscopic analysis of the stellar body of this galaxy using the MUSE integral-field spectrograph at the (ESO) Very Large Telescope. The MUSE datacube simultaneously provides DF2's stellar velocity field and systemic velocities for seven globular clusters (GCs). We further discovered three planetary nebulae (PNe) that are likely part of this galaxy. While five of the clusters had velocities measured in the literature, we were able to confirm the membership of two more candidates through precise radial velocity measurements, which increases the measured specific frequency of GCs in DF2. The mean velocity of the diffuse stellar body, 1792.9$^{-1.8}_{+1.4}$~\kms, is consistent with the mean globular cluster velocity. We detect a weak but significant velocity gradient within the stellar body, with a kinematic axis close to the photometric major-axis, making it a prolate-like rotator. We estimate a velocity dispersion from the clusters and PNe of $\sigma_{\mathrm{int}}=10.6^{+3.9}_{-2.3}$~\kms. The velocity dispersion $\sigma_{\rm{DF2}\star}$(\re) for the stellar body within one effective radius is $10.8^{-4.0}_{+3.2}$~\kms. Considering various sources of systemic uncertainties this central value varies between 5 and 13~\kms, and we conservatively report a 95\% confidence upper limit to the dispersion within one \re\ of 21~\kms. We provide updated mass estimates based on these dispersions corresponding to the different distances to NGC~1052-DF2 that have been reported in the recent literature.