Speaker
Description
This study uses cosmological `zoom-in' simulations to understand gas and metal mixing in a simulated Milky Way (MW)-mass galaxy's circumgalactic medium (CGM). To track mixing, we insert tracer dyes in the CGM representing diverse gas flows and physical properties, including shearing inflows-outflows, coherent inflows, coherent outflows, and static gas. We find that mixing is higher for strongly interacting inflows-outflows and generally depends on the local gas velocity dispersion. This is characterised by a high Spearman rank of 0.87 when correlating the dye spread 200 Myr after injection with velocity dispersion in a local 5 kpc box 100 Myr after the injection. Based on this, we construct generalised diffusion coefficient models that scale approximately linearly with velocity dispersion, as often assumed in subgrid mixing models used by smoothed particle hydrodynamics simulations. These models can approximate metal diffusion timescales for an MW-like CGM, a useful quantity to understand enrichment timescales for different types of metals. Lastly, we find that the gas mixing is roughly linear with time, suggesting superdiffusive behaviour in the CGM; thus, turbulent mixing is the major mechanism for diffusion in the CGM. These results provide a theoretical basis to predict diffusion coefficients from local gas properties to model processes like magnetic field diffusion, heat transport, and metal mixing.
