Gas-phase metallicity profiles of the Bluedisk galaxies: Is metallicity in a local star-formation regulated equilibrium?

TL;DR

This study examines the metallicity profiles of 50 galaxies, finding a correlation with HI mass fraction and suggesting metallicity may be regulated by local star formation in equilibrium.

Contribution

It introduces a simple analytical model explaining metallicity profiles and proposes that metallicity in isolated galaxies is regulated by local star formation.

Findings

Metallicity gradient correlates with HI mass fraction.

Outer disc metallicity drops are not exclusive to HI-rich galaxies.

A simple model accounts for the variety of metallicity profiles.

Abstract

As part of the Bluedisk survey we analyse the radial gas-phase metallicity profiles of 50 late-type galaxies We compare the metallicity profiles of a sample of HI-rich galaxies against a control sample of HI-'normal' galaxies. We find the metallicity gradient of a galaxy to be strongly correlated with its HI mass fraction (M(HI) / Mstar). We note that some galaxies exhibit a steeper metallicity profile in the outer disc than in the inner disc. These galaxies are found in both the HI-rich and control samples. This contradicts a previous indication that these outer drops are exclusive to HI-rich galaxies. These effects are not driven by bars, although we do find some indication that barred galaxies have flatter metallicity profiles. By applying a simple analytical model we are able to account for the variety of metallicity profiles that the two samples present. The success of this model implies that the metallicity in these isolated galaxies may be in a local equilibrium, regulated by star formation. This insight could provide an explanation of the observed local mass-metallicity relation.