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