Computational issues in chemo-dynamical modelling of the formation and evolution of galaxies

TL;DR

This paper investigates the challenges of accurately simulating chemical evolution in galaxy formation, highlighting resolution limits, stochastic supernova effects, and the importance of metal mixing schemes.

Contribution

It demonstrates the resolution threshold affecting scatter in simulations and proposes metal mixing schemes to improve accuracy in chemo-dynamical models.

Findings

Resolution below 10^3 M_sun increases scatter due to stochastic supernovae.

Metal mixing schemes reduce scatter to observed levels.

Best practices for simulating dwarf galaxies and the Milky Way are summarized.

Abstract

Chemo-dynamical N-body simulations are an essential tool for understanding the formation and evolution of galaxies. As the number of observationally determined stellar abundances continues to climb, these simulations are able to provide new constraints on the early star formaton history and chemical evolution inside both the Milky Way and Local Group dwarf galaxies. Here, we aim to reproduce the low $\alpha$-element scatter observed in metal-poor stars. We first demonstrate that as stellar particles inside simulations drop below a mass threshold, increases in the resolution produce an unacceptably large scatter as one particle is no longer a good approximation of an entire stellar population. This threshold occurs at around $10^3\,\rm{M_\odot}$, a mass limit easily reached in current (and future) simulations. By simulating the Sextans and Fornax dwarf spheroidal galaxies we show that this increase in scatter at high resolutions arises from stochastic supernovae explosions. In order to reduce this scatter down to the observed value, we show the necessity of introducing a metal mixing scheme into particle-based simulations. The impact of the method used to inject the metals into the surrounding gas is also discussed. We finally summarise the best approach for accurately reproducing the scatter in simulations of both Local Group dwarf galaxies and in the Milky Way.