GaiaData Release 2

Abstract

Context. Aims. The goal of this paper is to demonstrate the outstanding quality of the second data release of the Gaia mission and its power for constraining many different aspects of the dynamics of the satellites of the Milky Way. We focus here on determining the proper motions of 75 Galactic globular clusters, nine dwarf spheroidal galaxies, one ultra-faint system, and the Large and Small Magellanic Clouds. Methods. Using data extracted from the Gaia archive, we derived the proper motions and parallaxes for these systems, as well as their uncertainties. We demonstrate that the errors, statistical and systematic, are relatively well understood. We integrated the orbits of these objects in three different Galactic potentials, and characterised their properties. We present the derived proper motions, space velocities, and characteristic orbital parameters in various tables to facilitate their use by the astronomical community. Results. Our limited and straightforward analyses have allowed us for example to (i) determine absolute and very precise proper motions for globular clusters; (ii) detect clear rotation signatures in the proper motions of at least five globular clusters; (iii) show that the satellites of the Milky Way are all on high-inclination orbits, but that they do not share a single plane of motion; (iv) derive a lower limit for the mass of the Milky Way of 9.1-2.6+6.2 × 1011 M⊙ based on the assumption that the Leo I dwarf spheroidal is bound; (v) derive a rotation curve for the Large Magellanic Cloud based solely on proper motions that is competitive with line-of-sight velocity curves, now using many orders of magnitude more sources; and (vi) unveil the dynamical effect of the bar on the motions of stars in the Large Magellanic Cloud. Conclusions. All these results highlight the incredible power of the Gaia astrometric mission, and in particular of its second data release.

Simulating the spatial distribution and kinematics of globular clusters within galaxy clusters in illustris

“…GCs are among the densest stellar systems in the Universe, with typical stellar masses in the range [10 4 -10 6 M ] and sizes of only a few parsecs (Harris & Racine 1979;Brodie & Strader 2006). Be-consistent with the exquisite GCs data around the Milky Way (MW), other galaxies in the Local Group (Harris 1996;Gaia Collaboration et al 2018;Johnson et al 2015) and in massive ellipticals (Forbes et al 2011;Usher et al 2012;Taylor et al 2017). But in terms of numbers, the rich environment of nearby galaxy clusters, due to their high matter density and wide range of galaxy masses and morphologies, offer the best opportunity to understand the connection between GCs, galaxies and ultimately their dark matter halos.…”

The MAVERIC survey: a hidden pulsar and a black hole candidate in ATCA radio imaging of the globular cluster NGC 6397

“…A4 using stars within a 3 circular region centered on the cluster. We also make use of proper motion (PM) information from the Gaia database to confirm membership, only accepting sources that have PMs consistent with the cluster systematic PM (µ α = 3.2908 ± 0.0026 mas yr −1 , µ δ = −17.5908 ± 0.0025 mas yr −1 ; see Gaia Collaboration et al 2018b) at 5σ as cluster members.…”

The Milky Way bar/bulge in proper motions: a 3D view from VIRAC and Gaia

“…These are likely a combination of two effects. There are known systematics in the Gaia proper motion reference frame (Lindegren et al 2018), an example of which was observed in the LMC (Gaia Collaboration et al 2018b). Additionally there are possible variations in <µ l > and <µ b > on this scale due to variation in the average distance of the reference sources, causing a variation in the measured mean proper motions, caused by variable extinction.…”