The phase mixed debris of a massive merger as a dark matter subhalo detector

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• Elliot Davies
• Wednesday 30 November 2022, 13:15-14:05
• The Hoyle Lecture Theatre + Zoom .

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Recent work uncovered features in the phase space of the Milky Way’s stellar halo which may be attributed to the last major merger. When stellar material from a satellite is accreted onto its host, it phase mixes and appears finely substructured in phase space. For a high-eccentricity merger, this substructure most clearly manifests as numerous wrapping chevrons in (𝑣𝑟 , 𝑟) space, corresponding to stripes in (𝐸, 𝜃𝑟 ) space. We introduce the idea of using this substructure as an alternative subhalo detector to cold stellar streams. We simulate an N-body merger akin to the Gaia Sausage / Enceladus and assess the impact of subhaloes on these chevrons. To quantify the impact of perturbers, we utilise the simpler appearance of the chevrons in (𝐸, 𝜃𝑟 ) space. We show that a single flyby of a massive ( _{1010 M⊙) subhalo with pericentre comparable to, or within, the chevron’s apocentre smooths out the substructure, whereas a single flyby of a low mass (} 108 M⊙) has negligible effect. The effects of known massive perturbers (e.g. Sagittarius) could be detectable and offer constraints on their initial mass.

This talk is part of the Institute of Astronomy Seminars series.

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