Substructure at High Speed. I. Inferring the Escape Velocity in the Presence of Kinematic Substructure

The local escape velocity provides valuable inputs to the mass profile of Galaxy, and requires understanding tail stellar speed distribution. Following Leonard $\&$ Tremaine (1990), various works have since modeled distribution as $\propto (v_{\rm{esc}} -v)^k$, where $v_{\rm{esc}}$ is velocity, $k$ slope In such studies, however, these two parameters were found be largely degenerate often a narrow prior imposed on in order constrain $v_{\rm{esc}}$. Furthermore, validity power law form likely break down presence multiple kinematic substructures. this paper, we introduce strategy that for first time takes into account substructure. We model sum laws without imposing strong priors. Using mock data, show robustness method structure similar recently-discovered Gaia Sausage. companion present new measurement subsequently Milky Way using DR2 data.