Modelling the Tucana III stream - a close passage with the LMC

TL;DR

This study models the Tucana III stream's orbit, revealing a close passage with the LMC that influences its proper motion, with implications for understanding the LMC's mass and the Milky Way's potential.

Contribution

First dynamical fit of Tucana III stream considering the LMC's influence, predicting proper motions and highlighting the LMC's impact on the stream's dynamics.

Findings

Tucana III passed within 15 kpc of the LMC about 75 Myr ago.

Proper motion predictions depend on the assumed LMC mass.

LMC can induce a measurable proper motion perpendicular to the stream.

Abstract

We present results of the first dynamical stream fits to the recently discovered Tucana III stream. These fits assume a fixed Milky Way potential and give proper motion predictions, which can be tested with the upcoming Gaia Data Release 2. These fits reveal that Tucana III is on an eccentric orbit around the Milky Way and, more interestingly, that Tucana III passed within 15 kpc of the Large Magellanic Cloud (LMC) approximately 75 Myr ago. Given this close passage, we fit the Tucana III stream in the combined presence of the Milky Way and the LMC. We find that the predicted proper motions depend on the assumed mass of the LMC and that the LMC can induce a substantial proper motion perpendicular to the stream track. A detection of this misalignment will directly probe the extent of the LMC's influence on our Galaxy, and has implications for nearly all methods which attempt to constraint the Milky Way potential. Such a measurement will be possible with the upcoming Gaia DR2, allowing for a measurement of the LMC's mass.