Detecting Triaxiality in the Galactic Dark Matter Halo through Stellar Kinematics II: Dependence on Dark Matter and Gravity Nature

TL;DR

This study investigates how the shape of dark matter halos influences stellar kinematic groups in the Milky Way, finding that triaxiality is necessary for their formation regardless of dark matter type or gravity model.

Contribution

It demonstrates that stellar kinematic groups only form in triaxial halos, providing a potential observational test for dark halo shape and gravity theories.

Findings

Kinematic groups appear only in triaxial halos.

MOND gravity does not produce kinematic structures.

Halo shape influences stellar kinematic fossil signatures.

Abstract

Recent studies have presented evidence that the Milky Way global potential may be nonspherical. In this case, the assembling process of the Galaxy may have left long lasting stellar halo kinematic fossils due to the shape of the dark matter halo, potentially originated by orbital resonances. We further investigate such possibility, considering now potential models further away from $\Lambda$CDM halos, like scalar field dark matter halos, MOND, and including several other factors that may mimic the emergence and permanence of kinematic groups, such as, a spherical and triaxial halo with an embedded disk potential. We find that regardless of the density profile (DM nature), kinematic groups only appear in the presence of a triaxial halo potential. For the case of a MOND like gravity theory no kinematic structure is present. We conclude that the detection of these kinematic stellar groups could confirm the predicted triaxiality of dark halos in cosmological galaxy formation scenarios.