Constraining gas metal mixing strength in simulations using observations of the Milky Way's disc

TL;DR

This study constrains the metal mixing rate in the Milky Way's interstellar medium by comparing high-resolution simulations with observations, finding a specific mixing coefficient that best matches observed metallicity dispersions.

Contribution

It introduces observationally constrained mixing rates for simulations, improving the realism of ISM metallicity modeling in Milky Way-like galaxies.

Findings

Optimal mixing coefficient C = 0.0064 ± 0.0004

Power-law relationship between metal dispersion and C

ISM in the solar neighborhood is more mixed than some recent observations suggest

Abstract

This work explores the mixing rate of metals in the interstellar medium (ISM), comparing observational constraints from our solar neighbourhood to high resolution cosmological hydrodynamical simulations of Milky Way (MW)-like galaxies. The mixing rate, described by the coefficient C, is varied in simulations between 0 and 0.05, with resultant simulated galaxies compared to observations of metallicity dispersion in young star clusters, HII regions and neutral gas in the disc of the MW. A value of C between 0.003125 and 0.0125 is found to self-consistently match a range of observables, with a best estimate of C=0.0064$\pm$0.0004. We demonstrate that the relationship between metal dispersion in young stars, HII regions and neutral gas, versus the coefficient C, can be described by a power law. These constrained mixing rates infer a comparatively well mixed ISM in the solar neighbourhood, at odds with some recent observations that have reported a highly inhomogeneous ISM. The degree of mixing suggested by this work is lower than what often employed in many hydrodynamical simulations. Our results have implications for studying the metallicity distribution of stars as well as of gas in the interstellar and circumgalactic media.