Bar-halo interaction: the role of orbital anisotropy
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arXiv
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| Format: | Preprint |
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2026
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| author | Gherghinescu, Paula Fragkoudi, Francesca Deason, Alis |
| author_facet | Gherghinescu, Paula Fragkoudi, Francesca Deason, Alis |
| contents | We investigate the dynamical response of dispersion-dominated halo populations to a rotating galactic bar, focusing on how the underlying halo phase space distribution function (DF), and in particular the orbital anisotropy, shapes resonant structure formation. Using controlled test-particle simulations in a fixed Milky Way-like potential, we systematically vary the velocity anisotropy and net rotation of halo-like components while keeping the halo density profile, global potential, and bar properties fixed. We find that bar-induced resonances generate prominent substructure in energy-angular momentum space, but that the morphology, strength, and density contrast (i.e. overdensities versus underdensities) of these features depend sensitively on the halo orbital anisotropy and how resonant transport aligns with gradients of the DF in action space. For instance, radially biased halos tend to exhibit stronger responses and features across all main resonances. Our results also show that angular momentum exchange and the torque exerted on a halo are governed not only by its density profile but crucially by its orbital anisotropy structure. This highlights the importance of halo anisotropy when interpreting phase-space substructure in the stellar halo of the Milky Way with current and future surveys, while also having implications in further understanding the DM halo-bar coupling in disk galaxies. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_26225 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Bar-halo interaction: the role of orbital anisotropy Gherghinescu, Paula Fragkoudi, Francesca Deason, Alis Astrophysics of Galaxies We investigate the dynamical response of dispersion-dominated halo populations to a rotating galactic bar, focusing on how the underlying halo phase space distribution function (DF), and in particular the orbital anisotropy, shapes resonant structure formation. Using controlled test-particle simulations in a fixed Milky Way-like potential, we systematically vary the velocity anisotropy and net rotation of halo-like components while keeping the halo density profile, global potential, and bar properties fixed. We find that bar-induced resonances generate prominent substructure in energy-angular momentum space, but that the morphology, strength, and density contrast (i.e. overdensities versus underdensities) of these features depend sensitively on the halo orbital anisotropy and how resonant transport aligns with gradients of the DF in action space. For instance, radially biased halos tend to exhibit stronger responses and features across all main resonances. Our results also show that angular momentum exchange and the torque exerted on a halo are governed not only by its density profile but crucially by its orbital anisotropy structure. This highlights the importance of halo anisotropy when interpreting phase-space substructure in the stellar halo of the Milky Way with current and future surveys, while also having implications in further understanding the DM halo-bar coupling in disk galaxies. |
| title | Bar-halo interaction: the role of orbital anisotropy |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2605.26225 |