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

Journal Article · 23 February 2022 · The Astrophysical Journal

DOI: https://doi.org/10.3847/1538-4357/ac4243 · OSTI ID:1846307

Necib, Lina ; Lin, Tongyan

Abstract The local escape velocity provides valuable inputs to the mass profile of the galaxy, and requires understanding the tail of the stellar speed distribution. Following Leonard & Tremaine, various works have since modeled the tail of the stellar speed distribution as $\propto {(v_{\mathrm{esc}}-v)}^k$ , where v _esc is the escape velocity, and k is the slope of the distribution. In such studies, however, these two parameters were found to be largely degenerate and often a narrow prior is imposed on k in order to constrain v _esc . Furthermore, the validity of the power-law form can breakdown in the presence of multiple kinematic substructures or other mis-modeled features in the data. In this paper, we introduce a strategy that for the first time takes into account the presence of kinematic substructure. We model the tail of the velocity distribution as a sum of multiple power laws as a way of introducing a more flexible fitting framework. Using mock data and data from FIRE simulations of Milky Way-like galaxies, we show the robustness of this method in the presence of kinematic structure that is similar to the recently discovered Gaia Sausage. In a companion paper, we present the new measurement of the escape velocity and subsequently the mass of the Milky Way using Gaia eDR3 data.

• Sponsoring Organization: USDOE
• Grant/Contract Number: AC02-05CH11231; SC0019195; SC0011632
• OSTI ID: 1846307
• Journal Information: The Astrophysical Journal, Journal Name: The Astrophysical Journal Journal Issue: 2 Vol. 926; ISSN 0004-637X
• Publisher: American Astronomical SocietyCopyright Statement
• Country of Publication: United States
• Language: English