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Probing dark matter with resonant dynamics of the Galactic bar

Rimpei Chiba (CITA) // December 5, 2022

Abstract: I will present a novel evidence for dark matter obtained by measuring the deceleration of the Galactic bar. Galactic bars are linear stellar structures rotating at the centre of galactic disks and are known to spin down in the presence of dark matter haloes. The spin-down of the bar requires a transfer of energy and angular momentum to dark matter by dynamical friction, and therefore its measurement is in direct conflict with modified gravity theories. I will demonstrate that the slowdown of the Galactic bar can be quantified from the stars trapped in resonance with the bar: just like annual tree-rings, the resonant island in phase space evolves inside-out, capturing new stars by expanding its surface while conserving the internal distribution. Using the recent data from Gaia, I will show that corotation resonance of the bar bears this tree-ring structure, allowing us to infer slowdown history of the bar. In the latter part, I will also present a new approach to model dynamical friction in the realistic nonlinear/slow regime.

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