SDSS-IV MaNGA: galaxy gas-phase metallicity gradients vary across the mass-size plane

TL;DR

This study examines how gas-phase metallicity gradients in galaxies vary across the combined mass and size plane, revealing a systematic pattern that depends on galaxy size at fixed mass, with implications for galaxy evolution.

Contribution

It is the first to analyze gas-phase metallicity gradients across the galaxy mass--size plane, uncovering a new systematic variation not explained by previous models.

Findings

Gradients vary systematically with mass and size.

Smaller galaxies above 10^10 M_sun have flatter gradients.

The pattern is not due to instrumental effects or morphology.

Abstract

Gas-phase abundances and abundance gradients provide much information on past stellar generations, and are powerful probes of how galaxies evolve. Gas abundance gradients in galaxies have been studied as functions of galaxies' mass and size individually, but have largely not been considered across the galaxy mass--size plane. Thus, we investigate gas-phase abundance gradients across this plane, using a sample of over 1000 galaxies selected from the MApping Nearby Galaxies at APO (MaNGA) spectroscopic survey. We find that gradients vary systematically such that above $10^{10}M_{\odot}$, smaller galaxies display flatter gradients than larger galaxies at a given stellar mass. This mass--size behaviour cannot be explained by instrumental effects, nor is it simply a reflection of known trends between gradients and morphology. We explore multiple possibilities for a physical origin for this pattern, though further work is needed to establish a firm physical interpretation.