Gaia early DR3 systemic motions of Local Group dwarf galaxies and orbital properties with a massive Large Magellanic Cloud^⋆

¹ Instituto de Astrofísica de Canarias, Calle Vía Láctea s/n, 38206 La Laguna, Tenerife, Spain
e-mail: gbattaglia@iac.es
² Universidad de La Laguna, Avda. Astrofísico Fco. Sánchez, 38205 La Laguna, Tenerife, Spain

Received: 11 June 2021
Accepted: 28 July 2021

Abstract

Aims. We perform a comprehensive determination of the systemic proper motions of 74 dwarf galaxies and dwarf galaxy candidates in the Local Group based on Gaia early data release 3. The outputs of the analysis for each galaxy, including probabilities of membership, will be made publicly available. The analysis is augmented by a determination of the orbital properties of galaxies within 500 kpc.

Methods. We adopt a flexible Bayesian methodology presented in the literature, which takes into account the location of the stars on the sky, on the colour-magnitude diagram, and on the proper motion plane. We applied some modifications, in particular to the way the colour-magnitude diagram and spectroscopic information are factored in, for example, by including stars in several evolution phases. The bulk motions were integrated in three gravitational potentials: two where the Milky Way was treated in isolation and has a mass 0.9 & 1.6 × 10¹² M_⊙, and a time-varying potential, which includes the infall of a massive Large Magellanic Cloud (LMC).

Results. We were able to determine bulk proper motions for 73 systems, and we consider 66 to be reliable measurements. For the first time, systemic motions are presented for galaxies out to a distance of 1.4 Mpc in the NGC 3109 association. The inclusion of the infall of a massive LMC significantly modifies the orbital trajectories of the objects, with respect to orbit integration in static Milky-Way-only potentials, and this leads to six galaxies likely being associated with the LMC, three possibly being associated with it, and one recently captured object. We discuss the results of the orbit integration in the context of the relation of the galaxies to the system of Milky Way satellites, implications for the too-big-to-fail problem, the impact on star formation histories, and tidal disruption.