Resonance Sweeping in Barred Galaxy Simulations

Theory suggests that galactic bars spin down throughout their evolution due to an angular momentum exchange with the inner parts of their dark matter halos. As opposed to a bar with a fixed pattern speed, Chiba et al. (2019) proposed that ‘resonance sweeping’ due to a decelerating galactic bar can explain local kinematic substructure in the solar neighborhood, like the Hercules stream. To date, resonance sweeping — a process of trapping and dragging the orbits of stars — has been explored both analytically and with test particle simulations that lack self-gravity. Here, we take such analyses a step further and examine resonance sweeping with a high resolution (~10⁹ particle) self-consistent N-body simulation. Like Chiba et al. (2019), the bar patten speed in our adopted simulated galaxy slowly decelerates over the course of the simulation, with Ω_bar decreasing from 49.88 to 28.84 km s^-1 kpc^-1 in 4 Gyr (ΔΩ_bar/Δt = 5.25 km s^-1 kpc^-1 Gyr^-1). For our preliminary test, we calculated frequencies of the stars using AGAMA. We identify stars in Corotation Resonance and Outer Lindblad Resonance and find a significant number of stars remain in resonance later in time suggesting resonant sweeping of orbits due to the decelerating bar. This result in a more realistic, self-gravitating disk indicates that the method of resonance sweeping can indeed be applied to Gaia data.