Kinematics of the Sagittarius dwarf spheroidal core: a 5D analysis for a 6D methodology with Gaia DR3

Abstract

Using Gaia Data Release 3 data, we examine the kinematics of the central core of the Sagittarius (Sgr) dwarf spheroidal galaxy using data that include 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 βa = −2.24 ± 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.