# A Predicted Correlation Between Age Gradient and Star Formation History in FIRE Dwarf Galaxies

## TL;DR

This study uses FIRE simulations to analyze how star formation history varies radially in dwarf galaxies, revealing common age gradients influenced by mergers and feedback, which can bias observational interpretations.

## Contribution

It introduces a detailed analysis of age gradients in dwarf galaxies across a range of masses, highlighting the roles of mergers and feedback in shaping these gradients.

## Key findings

- Older stars are more common at larger radii.
- Age gradient strength correlates with galaxy age.
- Mergers and feedback significantly influence age gradients.

## Abstract

We explore the radial variation of star formation histories in dwarf galaxies simulated with Feedback In Realistic Environments (FIRE) physics. The sample contains 9 low-mass field dwarfs with M_ star = 10^5 - 10^7 M_sun from previous FIRE results, and a new suite of 17 higher mass field dwarfs with M_star = 10^7 - 10^9 M_sun introduced here. We find that age gradients are common in our dwarfs, with older stars dominant at large radii. The strength of the gradient correlates with overall galaxy age such that earlier star formation produces a more pronounced gradient. The relation between formation time and strength of the gradient is driven by both mergers and star-formation feedback. Mergers can both steepen and flatten the age gradient depending on the timing of the merger and star formation history of the merging galaxy. In galaxies without significant mergers, early feedback pushes stars to the outskirts at early times. Interestingly, among galaxies without mergers, those with large dark matter cores have flatter age gradients because these galaxies have more late-time feedback. If real galaxies have age gradients as we predict, stellar population studies that rely on sampling a limited fraction of a galaxy can give a biased view of its global star formation history. We show that central fields can be biased young by a few Gyrs while outer fields are biased old. Fields positioned near the 2D half-light radius will provide the least biased measure of a dwarf galaxy's global star formation history.