The MAGPI Survey: forward modelled gas-phase metallicity gradients in galaxies at $z\sim 0.3$

TL;DR

This study measures gas-phase metallicity gradients in 70 galaxies at z~0.3 using Bayesian modelling, revealing their relation to galaxy properties and the influence of turbulence, mass, and gas flows on metallicity distribution.

Contribution

It introduces a Bayesian approach with Blobby3D to accurately measure metallicity gradients accounting for seeing effects, providing new insights into galaxy evolution mechanisms.

Findings

Median metallicity gradient is approximately -0.013 dex/kpc.

A positive correlation exists between metallicity gradient and gas velocity dispersion.

Smaller galaxies tend to have flatter or positive metallicity gradients.

Abstract

We measure the seeing-deconvolved gas-phase metallicity gradients of 70 star-forming galaxies at $z\sim 0.3$ from the MAGPI survey and investigate their relationship with galaxy properties to understand the mechanisms that influence the distribution of metals and shape the evolution of the galaxies. We use a Bayesian modelling technique, Blobby3D, which accounts for seeing effects (beam smearing) and can model the substructures of the flux distribution. The median metallicity gradient of our sample is $\nabla \mathrm{[O/H]}=-0.013^{+0.059}_{-0.033}$ dex/kpc. Among the galaxies in our sample, 32.9% have negative metallicity gradients (2$\sigma$ significance), 10.0% have positive gradients and 57.1% have flat gradients. The $\nabla \mathrm{[O/H]}$-$M_*$ relation of the MAGPI galaxies generally agrees with theoretical predictions, where a combination of stellar feedback, gas transport, and accretion shapes the metallicity profile, with the dominant processes varying with galaxy mass. We find a positive correlation between $\nabla \mathrm{[O/H]}$ and gas velocity dispersion ($r=0.36$), indicating that stronger gas turbulence is associated with flatter or inverted metallicity gradients, likely due to enhanced gas mixing. Additionally, smaller galaxies tend to have flatter or positive gradients, suggesting that metal dilution by gas accretion or removal via feedback-driven winds may outweigh metal enrichment in small galaxies.