Action and energy clustering of stellar streams in deforming Milky Way dark matter haloes

TL;DR

This study examines how non-adiabatic deformations of the Milky Way's halo, caused by the Large Magellanic Cloud, affect stellar stream analysis, revealing that action clustering methods can recover mass profiles for some streams but fail for others with close encounters.

Contribution

It introduces a time-evolving MW--LMC simulation to assess the impact of halo deformations on stellar stream action clustering methods, highlighting their limitations and potential alternatives.

Findings

Action clustering recovers MW mass profile for short-period streams without close LMC encounters.

Deformations disperse action clustering for streams with long periods and close LMC interactions.

Stream energy clustering is less sensitive to halo deformations, offering an alternative constraint method.

Abstract

We investigate the non-adiabatic effect of time-dependent deformations in the Milky Way (MW) halo potential on stellar streams. Specifically, we consider the MW's response to the infall of the Large Magellanic Cloud (LMC) and how this impacts our ability to recover the spherically averaged MW mass profile from observation using stream actions. Previously, action clustering methods have only been applied to static or adiabatic MW systems to constrain the properties of the host system. We use a time-evolving MW--LMC simulation described by basis function expansions. We find that for streams with realistic observational uncertainties on shorter orbital periods and without close encounters with the LMC, e.g. GD-1, the radial action distribution is sufficiently clustered to locally recover the spherical MW mass profile across the stream radial range within a 2 sigma confidence interval determined using a Fisher information approach. For streams with longer orbital periods and close encounters with the LMC, e.g. Orphan-Chenab (OC), the radial action distribution disperses as the MW halo has deformed non-adiabatically. Hence, for OC streams generated in potentials that include a MW halo with any deformations, action clustering methods will fail to recover the spherical mass profile within a 2 sigma uncertainty. Finally, we investigate whether the clustering of stream energies can provide similar constraints. Surprisingly, we find for OC-like streams, the recovered spherically averaged mass profiles demonstrate less sensitivity to the time-dependent deformations in the potential.