MIKiS: The Multi-instrument Kinematic Survey of Galactic Globular Clusters. I. Velocity Dispersion Profiles and Rotation Signals of 11 Globular Clusters*

Abstract

We present the first results of the Multi-Instrument Kinematic Survey of Galactic Globular Clusters, a project aimed at exploring the internal kinematics of a representative sample of Galactic globular clusters from the radial velocity of individual stars, covering the entire radial extension of each system. This is achieved by exploiting the formidable combination of multiobject and integral field unit spectroscopic facilities of the ESO Very Large Telescope. As a first step, here we discuss the results obtained for 11 clusters from high and medium resolution spectra acquired through a combination of FLAMES and KMOS observations. We provide the first kinematical characterization of NGC 1261 and NGC 6496. In all the surveyed systems, the velocity dispersion profile declines at increasing radii, in agreement with the expectation from the King model that best fits the density/luminosity profile. In the majority of the surveyed systems we find evidence of rotation within a few half-mass radii from the center. These results are in general overall agreement with the predictions of recent theoretical studies, suggesting that the detected signals could be the relic of significant internal rotation set at the epoch of the cluster's formation.

Systematic errors in Gaia DR2 astrometry and their impact on measurements of internal kinematics of star clusters

“…• Line-of-sight velocity dispersion profiles from the MUSE IFU (Kamann et al 2018), MIKiS survey (Ferraro et al 2018), and a compilation of various sources and own measurements by Baumgardt & Hilker (2018) and Baumgardt et al (2019). In order to convert these data from km s −1 to mas yr −1 , we used the distances determined by Baumgardt et al (2019), even though our own PM dispersion profiles may be somewhat different from theirs.…”

“…A few other clusters also have possible signs of rotation: Pal 7 (IC 1276), NGC 5986, NGC 6093 (M 80), NGC 6341 (M 92), NGC 6388, NGC 6402 (M14); additional tests with different subsets of stars confirm the persistence of these signatures, but their significance is low ( 2σ level), especially for the last three clusters. Most of these clusters have been found to be rotating based on line-of-sight velocity measurements, or their combination with Gaia PM: NGC 4372(Kacharov et al 2014), NGC 5272(Fabricius et al 2014, Ferraro et al 2018, Sollima et al 2019), NGC 5986 (Lanzoni et al 2018, NGC 6093, NGC 6341(Fabricius et al 2014, Sollima et al 2019), NGC 6388 (Lanzoni et al 2013 Kamann et al 2018)…”

The WAGGS project-III. Discrepant mass-to-light ratios of Galactic globular clusters at high metallicity

“…However, as our analysis explicitly accounts for these effects, we are confident that our values are robust against such contamination. Figure 9 shows our derived cluster masses compared to Kimmig et al (2015); Ferraro et al (2018); Baumgardt et al (2019a). As before, three of the Kimmig et al (2015) cluster values are the most discrepant, although for different GCs: NGCs 288, 6809, and 6838.…”

“…We compare our derived velocity dispersions and masses with previous work: 20 clusters overlap with the Kimmig et al (2015) sample; and ten can be compared to Ferraro et al (2018). The central velocity dispersions derived by each study are (King) model predictions based on velocity dispersions further out.…”

“…Now with HST and the development of integral-field units (IFUs) like MUSE, studies can measure the motions of thousands of stars -including those in the cluster centres -for the first time (e.g. Bellini et al 2014Bellini et al , 2017bKamann et al 2018;Ferraro et al 2018). This has opened up new avenues to uncover the populations of central stellar remnants, like stellar-mass black holes (e.g.…”