Galactic Orbits of Selected Companions of the Milky Way

TL;DR

This study calculates the three-dimensional orbits of 11 dwarf galaxy companions of the Milky Way using high-precision measurements and refined galactic potential models, revealing most are tightly bound while Leo I is weakly bound.

Contribution

It provides detailed orbital analyses of Milky Way companions using updated models and measurements, highlighting their gravitational binding status.

Findings

Most galaxies are tightly gravitationally bound to the Milky Way.

Leo I is only weakly gravitationally bound despite higher mass models.

Orbital characteristics depend on the assumed galactic potential and mass.

Abstract

High-accuracy absolute proper motions, radial velocities, and distances have now been measured for a number of dwarf-galaxy companions of the Milky Way, making it possible to study their 3D dynamics. Galactic orbits for 11 such galaxies (Fornax, Sagittarius, Ursa Minor, LMC, SMC, Sculptor, Sextans, Carina, Draco, Leo I, Leo II) have been derived using two previously refined models for the Galactic potential with the Navarro-Frenk-White and Allen-Santill'an expressions for the potential of the dark-matter halo, and two different masses for the Galaxy within 200 kpc - 0.75x10^12 Mo and 1.45x10^12 Mo. The character of the orbits of most of these galaxies indicates that they are tightly gravitationally bound to the Milky Way, even with the lower-mass model for the gravitational potential. One exception is the most distant galaxy in the list, Leo I, whose orbit demonstrates that it is only weakly gravitationally bound, even using the higher-mass model of the gravitational potential.