# Spatial Variations of Stellar Elemental Abundances in FIRE Simulations of Milky Way-Mass Galaxies: Patterns Today Mostly Reflect Those at Formation

**Authors:** Russell L. Graf, Andrew Wetzel, Matthew A. Bellardini, Jeremy Bailin  
**arXiv:** [2402.15614](https://arxiv.org/abs/2402.15614)  
**Date:** 2024-02-23  
**Summary page:** https://www.summarizepaper.com/en/paper/2402.15614v1/

## Key points

- Investigating spatial variations of stellar elemental abundances in Milky Way (MW)-mass galaxies using FIRE cosmological zoom-in simulations
- Analyzing radial, vertical, and azimuthal distributions of metals in stars at present day and during formation
- Radial gradient of metals steeper for younger stars, consistent with MW observations
- Negative vertical gradients across all stars due to disk vertical settling, weak within mono-age populations
- Vertical gradients shallower at larger radii but less pronounced overall
- Azimuthal scatter relatively constant with radius and age up to around 8 billion years ago, increases for older stars
- Galaxies with larger azimuthal scatter tend to have stronger radial gradients
- Spatial variations in stellar metallicities show modest differences between formation and present-day conditions
- Initial conditions of stars at birth predominantly influence observed spatial patterns

## Summary

In this study, we investigate the spatial variations of stellar elemental abundances in Milky Way (MW)-mass galaxies using the Feedback In Realistic Environments (FIRE) cosmological zoom-in simulations. Our goal is to gain insights into the formation history of galaxies by analyzing the radial, vertical, and azimuthal distributions of metals in stars at present day and during their formation. Our findings reveal that the radial gradient of metals is steeper for younger stars, consistent with observations in the MW. Interestingly, this age dependence was already evident at birth and remains relatively unchanged over time. We also observe negative vertical gradients across all stars due to disk vertical settling, although these gradients are weak within mono-age stellar populations. Similar to the MW, our simulations show that vertical gradients are shallower at larger radii but overall less pronounced. This trend was also established at birth and has remained relatively constant until present day. Additionally, our analysis reveals that azimuthal scatter remains relatively constant with radius and age up to around 8 billion years ago but increases for older stars. Galaxies with larger azimuthal scatter tend to have stronger radial gradients, suggesting that current azimuthal scatter primarily arises from the redistribution of gas and stars along the radial direction. Overall, our results suggest that spatial variations in stellar metallicities exhibit modest differences between formation and present-day conditions. The observed spatial patterns predominantly reflect the initial conditions of stars at birth rather than post-birth redistribution processes. Through detailed simulations and comparisons with observational data from the MW and nearby galaxies, we gain valuable insights into the complex interplay between galaxy formation processes and stellar elemental abundances.