Proper Motions, Orbits, and Tidal Influences of Milky Way Dwarf Spheroidal Galaxies (2205.05699v2)

Abstract: We combine Gaia EDR3 astrometry with accurate photometry and utilize a probabilistic mixture model to measure the systemic proper motion of 52 dwarf spheroidal (dSph) satellite galaxies of the Milky Way (MW). For the 46 dSphs with literature line-of-sight velocities we compute orbits in both a MW and a combined MW + Large Magellanic Cloud (LMC) potential and identify Car II, Car III, Hor I, Hyi I, Phx II, and Ret II as likely LMC satellites. 40% of our dSph sample has a >25% change in pericenter and/or apocenter with the MW + LMC potential. For these orbits, we Monte Carlo sample over the observational uncertainties for each dSph and the uncertainties in the MW and LMC potentials. We predict that Ant II, Boo III, Cra II, Gru II, and Tuc III should be be tidally disrupting by comparing each dSph's average density relative to the MW density at its pericenter. dSphs with large ellipticity (CVn I, Her, Tuc V, UMa I, UMa II, UMi, Wil 1) show a preference for their orbital direction to align with their major axis even for dSphs with large pericenters. We compare the dSph radial orbital phase to subhalos in MW-like N-body simulations and infer that there is not an excess of satellites near their pericenter. With projections of future Gaia data releases, we find dSph orbital precision will be limited by uncertainties in the distance and/or MW potential rather than proper motion precision. Finally, we provide our membership catalogs to enable community follow-up.

• The paper derives systemic proper motions for 52 dSphs using Gaia EDR3, confirming significant orbital alterations under the LMC's gravitational influence.
• The analysis identifies tidal disruption in several dSphs by comparing their densities at MW pericenters with orbital alignments and ellipticity indicators.
• The methodology employs probabilistic mixture models and dual background comparisons to enhance kinematic precision, shaping future observational strategies.

Analysis of Proper Motions, Orbits, and Tidal Influences of Milky Way Dwarf Spheroidal Galaxies

This paper presents a comprehensive paper on the proper motions, orbital dynamics, and the gravitational influences of the Milky Way (MW) and Large Magellanic Cloud (LMC) on a sample of 52 dwarf spheroidal (dSph) galaxies. By leveraging the precise astrometry from the Gaia Early Data Release 3 (EDR3) in conjunction with auxiliary photometry, the authors employ a probabilistic mixture model to derive systemic proper motions. The subsequent analysis explores the orbital characteristics and potential tidal disruptions of these satellite galaxies.

Key Findings and Methodological Approaches

1. Proper Motions and Orbits: The paper confirms systemic proper motions for 52 dSphs, utilizing two distinct background models for cross-verification. These proper motions facilitate the computation of orbits, acknowledging the dual potential fields of the MW and the influential LMC. The paper highlights that 40% of the dSphs experience significant alterations in their orbital parameters due to the presence of the LMC.
2. Tidal Disruption Indicators: The analysis identifies Ant II, Boo III, Cra II, Gru II, and Tuc III as likely to be undergoing tidal disruption. This conclusion is drawn by comparing each dSph's average density to that of the MW at their pericenters. The findings are corroborated by additional indicators such as ellipticity and alignment between orbital paths and tidal features.
3. LMC Satellite Identification: Six dSphs, namely Car II, Car III, Hor I, Hyi I, Phx II, and Ret II, are identified as probable LMC satellites, owing to their significant orbital changes when the LMC's gravitational influence is considered.
4. Future Precision Limitations: Projections using future Gaia data releases suggest that while proper motion precision will improve, the limiting factors for orbital precision will be distance accuracies and the MW potential uncertainties.

Implications and Theoretical Speculations

The paper's findings have several implications for the understanding of galactic dynamics and the evolution of the MW's satellite system:

• Dynamical Interactions and Satellite Histories: The paper underscores the complex dynamical interactions between the MW, its satellite galaxies, and external bodies like the LMC. Such interactions are pivotal in shaping the structural and dynamical evolution of satellite galaxies.
• Galactic Halo Mass and Structure: The results also provide constraints on the MW halo structure and its mass distribution, which are crucial for verifying models of dark matter distribution and understanding the MW evolution.
• Future Observational Strategies: This paper lays a robust groundwork for targeted observational campaigns that could enhance our comprehension of satellite galaxy dynamics. Future observations, particularly with improved distance measurements and detailed kinematic studies, will play a crucial role in refining these models.

In conclusion, the paper presents critical insights into the proper motion analysis and orbital dynamics of MW dwarf spheroidals. By addressing the influences of both the MW and LMC, the paper enhances our understanding of the gravitational interplay within this cosmic neighborhood. Future Gaia releases are poised to augment these findings, further elucidating the intricacies of satellite galaxy dynamics in the MW system.