Secular Bars Public

We will design and conduct a series of isolated hydrodynamic simulations of galaxies at parsec resolution. This approach will allow us to keep full control of the initial conditions, and to freely select, modify, and combine different physical ingredients while maintaining all other parameters fixed, in order to precisely determine their impact. These simulations will be performed using the adaptive mesh refinement code RAMSES (Teyssier 2002) which includes all the relevant ingredients, i.e. gas cooling and heating, star formation, and feedback. The initial conditions of individual runs will be varied to explore a large range of parameters and their impact on the formation and evolution of bars. Among them, a particular focus will be on the gas fraction, bulge properties (e.g. mass, concentration), and dark matter halo profile, as these aspects are suspected to strongly influence disc instabilities and the exchange of angular momentum with bars. We will complement this exploration with variations of the effects of subgrid models, mostly star formation and feedback.

In parallel, we will focus on the development of analytical tools to provide a robust interpretation of the numerical results. We will characterise the initial conditions of various idealised simulations through a phase-space distribution whose self-gravitating evolution under an initial small perturbation can be analytically followed, through linear and secular response theory (Roule et al. 2022, Rozier et al. 2025). The present study will describe both a thickened disc and the halo, to fully capture the complexity of the resonances at play in such a system. This simplified analytic approach will treat the impact of the gas as an external source of potential fluctuations, and capture the key dynamical mechanisms at play in the isolated galaxy simulations, which in turn will shed light on what is currently missing from large-scale cosmological simulations

Finally, while this project is designed within the ΛCDM context, should the solution to the modelling problem come down to the fundamental nature of dark matter, we will extend our numerical and theoretical work by modifying the dark sector. Possible extensions for which our team has expertise involve fuzzy dark matter or MOND gravity (e.g. Hu et al. 2000, Famaey & McGaugh 2012, Bar Or et al. 2019). Additionally, an interesting venue is provided by primordial galaxy-scale non-Gaussianities in the initial conditions of galaxy formation and evolution models, which could change the environment of galaxy formation (Stahl et al. 2024).