Comparing radial migration in dark matter and MOND regimes

¹ Faculty of Mathematics, Physics, and Informatics, Comenius University, Mlynská dolina, 842 48 Bratislava, Slovakia
² Astros Solutions s. r. o. Nad Lúčkami 35, 841 04 Bratislava, Slovakia

^★ Corresponding author; roman.nagy@fmph.uniba.sk

Received: 4 September 2024
Accepted: 22 November 2024

Abstract

Context. Multiple studies on radial migration in disc galaxies have proven the importance of the effect of resonances with non- axisymmetric components on the evolution of galactic discs. However, the dynamical effects of classic Newtonian dynamics with dark matter (DM) differ from MOdified Newtonian Dynamics (MOND) and might trigger different radial migration. A thorough analysis of radial migration considering these two gravitational regimes might shed some light on different predictions of DM and MOND theories.

Aims. We aim to quantitatively and qualitatively compare the effects of resonances and stellar radial migration (churning) in a Milky Way-like (MW-like) galaxy in the DM and MOND regimes. We performed numerical simulations of a MW-like galaxy to analyse the effect of non-axisymmetric structures (galactic bar and spiral arms) considering various parameters of the spiral structure.

Methods. We conducted a two-dimensional numerical simulation consisting of the integration of 2 · 10⁶ stars in a static rotating galactic potential for 6 Gyr. We analysed the changes in the stellar disc caused by stellar radial migration. To study the effects of radial migration and resonances in detail, we analysed the change in the star’s position, the guiding radius, as well as the frequency phase space. We investigated DM and MOND approaches.

Results. The outcome of the simulation shows that the radial migration is much more pronounced in the MOND regime compared to the DM one. Increasing both the spiral amplitude and the spiral pattern speed results in more prominent radial migration. Compared to the DM approach, in the MOND regime, we observe up to five times as many stars with a maximum change in the guiding radius of more than 1.5 kpc during the time interval from 2–6 Gyr. Increasing the amplitude of the spiral structure amplifies this effect. On the other hand, increasing the spiral pattern speed reduces the difference between DM and MOND. Analysis of the frequency phase space reveals that the most prominent resonances in all DM and MOND configurations are the co-rotation resonance with the spiral arms (m = p = 1), outer Lindblad resonance with the galactic bar and spiral arms, and the co-rotation resonance (m = 2, p = 1) with the superposition of the galactic bar and spiral arms, 2Ω = Ω_b + Ω_sp.