Kinematics of the Sagittarius Dwarf Spheroidal core: A 5D Analysis for a 6D Methodology with Gaia DR3

TL;DR

This study utilizes Gaia DR3 data to analyze the kinematics of the Sagittarius dwarf galaxy's core using a novel 5D methodology, improving measurements of dark matter profiles and stellar orbits.

Contribution

It introduces a 5D analysis framework combining proper motions, line-of-sight velocities, and projected positions, enhancing kinematic measurements of dwarf galaxy cores.

Findings

Velocity anisotropy indicates tangentially-biased orbits.

Full 5D data significantly improves dark matter profile measurements.

Mock data tests show an order of magnitude error reduction.

Abstract

Using Gaia DR3 data, we examine the kinematics of the central core of the Sagittarius (Sgr) dwarf spheroidal galaxy using data which includes proper motions and line-of-sight velocities for member stars in addition to their projected positions. We extract a sample of bright stars that are high-probability members of Sgr. We model the distances to these stars, which is the only missing phase-space component measurement from our 5D sample, highlighting how their corresponding uncertainties propagate to affect the kinematics. Using line-of-sight velocity data only, which are not affected by the distance uncertainties, and assuming a jeans-based equilibrium analysis, we obtain a velocity anisotropy of $\beta_a = -2.24 \pm 1.99$, which implies a system with tangentially-biased orbits. With the full 5D data, we project that the data will significantly improve upon measurements of the log-slope of the dark matter density profile and the stellar velocity anisotropy. Tests with mock distance data show an improvement of anisotropy errors of approximately an order of magnitude, and log slope at the half light radius of approximately half an order of magnitude.