Tango for three: Sagittarius, LMC, and the Milky Way (2009.10726v2)

Abstract: We assemble a catalogue of candidate Sagittarius stream members with 5d and 6d phase-space information, using astrometric data from Gaia DR2, distances estimated from RR Lyrae stars, and line-of-sight velocities from various spectroscopic surveys. We find a clear misalignment between the stream track and the direction of the reflex-corrected proper motions in the leading arm of the stream, which we interpret as a signature of a time-dependent perturbation of the gravitational potential. A likely cause of this perturbation is the recent passage of the most massive Milky Way satellite - the Large Magellanic Cloud (LMC). We develop novel methods for simulating the Sagittarius stream in the presence of the LMC, using specially tailored N-body simulations and a flexible parametrization of the Milky Way halo density profile. We find that while models without the LMC can fit most stream features rather well, they fail to reproduce the misalignment and overestimate the distance to the leading arm apocentre. On the other hand, models with an LMC mass in the range (1.3+-0.3)x10^11 Msun rectify these deficiencies. We demonstrate that the stream can not be modelled adequately in a static Milky Way. Instead, our Galaxy is required to lurch toward the massive in-falling Cloud, giving the Sgr stream its peculiar shape and kinematics. By exploring the parameter space of Milky Way potentials, we determine the enclosed mass within 100 kpc to be (5.6+-0.4)x10^11 Msun, and the virial mass to be (9.0+-1.3)x10^11 Msun, and find tentative evidence for a radially-varying shape and orientation of the Galactic halo.

• The paper demonstrates that the LMC’s fly-by significantly perturbs the Milky Way’s potential, causing misalignments in the Sagittarius stream’s proper motions.
• The authors leverage Gaia DR2, RR Lyrae data, and spectroscopic surveys with innovative N-body simulations to refine stream dynamics modeling.
• Findings indicate a shift in the Milky Way halo shape and suggest reduced total mass estimates, prompting revised views on galactic structure and evolution.

The Dynamic Interaction of the Milky Way, Sagittarius Stream, and the Large Magellanic Cloud

In the paper "Tango for three: Sagittarius, LMC, and the Milky Way," Vasiliev, Belokurov, and Erkal present a comprehensive investigation into the dynamical interactions between the Milky Way galaxy, its nearby satellite galaxies—the Sagittarius (Sgr) dwarf galaxy and the Large Magellanic Cloud (LMC)—and their joint influence on the Sgr stream. The primary focus of this research is to dissect the complex gravitational interplay between these celestial systems, especially considering the perturbative effects induced by the massive LMC fly-by and the associated reflex motion of the Milky Way.

Using a sophisticated combination of data from Gaia DR2, RR Lyrae stars, and spectroscopic surveys, the authors assemble a detailed catalogue of candidate members of the Sgr stream. Notably, they identify a significant misalignment between the stream's predicted trajectory and the direction of its reflex-corrected proper motions, particularly evident in the leading arm. This discrepancy is posited as evidence for a time-dependent perturbation of the Milky Way's gravitational potential, which they attribute to the recent passage of the LMC.

The research introduces novel methodologies for simulating the Sgr stream dynamics in a time-evolving gravitational potential influenced by both the Milky Way's halo and the LMC's mass. By employing a combination of restricted and full $N$-body simulations, the authors navigate the complexities of modeling such a dynamically rich system. These simulations underscore that static models of the Milky Way fail to adequately account for the observed stream features, especially the proper motion misalignment and overestimation of the leading arm's apocenter distance. Instead, incorporating the dynamic influence of the LMC, with a mass range of $(1.3\pm0.3)\times10^{11}\,M_\odot$, aligns with the observations, yielding a more accurate portrayal of the stream's peculiar morphology and kinematics.

The implications of this work are profound both theoretically and practically. The accurate modeling of the Sgr stream provides crucial insights into the Milky Way’s halo shape, demanding a transition from an oblate, disc-aligned inner halo to a more prolate configuration in the outer regions. These findings resonate with contemporary models of cosmic structure formation and halo configuration in galaxy evolution scenarios. Moreover, the inferred mass of the LMC and its first approach to the Milky Way prompts a reevaluation of the Milky Way’s mass distribution, suggesting a lower total mass compared to earlier standalone Milky Way models.

This research represents a significant contribution to the paper of galactic dynamics and the role of satellite interactions. It brings to light the necessity of considering the reflex motion of larger stellar systems in response to massive satellites, effectively demonstrating the dynamic nature of galaxy evolution.

Further explorations could delve into refining these dynamic models with enhanced resolution in both observational data and simulation precision. Such efforts would extend the understanding of minor satellite interactions and their broader cosmological implications. The interplay between the Milky Way, its satellite galaxies, and the accreting streams represents a vibrant field of astronomical inquiry that promises to unlock hidden features of our galaxy's evolution and structure.