The effects of dynamical substructure on Milky Way mass estimates from the high velocity tail of the local stellar halo

Understand

We investigate the impact of dynamical streams and substructure on estimates of the local escape speed and total mass of Milky Way-mass galaxies from modelling the high velocity tail of local halo stars.

• We use a suite of high-resolution, magneto-hydrodynamical cosmological zoom-in simulations, which resolve phase space substructure in local volumes around solar-like positions.
• We show that phase space structure varies significantly between positions in individual galaxies and across the suite.
• Substructure populates the high velocity tail unevenly and leads to discrepancies in the mass estimates.