The Comparative Chemical Evolution of an Isolated Dwarf Galaxy: A VLT and Keck Spectroscopic Survey of WLM

TL;DR

This study compares the chemical evolution of the isolated dwarf galaxy WLM with other Local Group dwarfs, revealing similarities in metallicity and a potential link between angular momentum and metallicity gradients.

Contribution

It provides the first detailed comparison of WLM's metallicity distribution with other dwarf galaxies, highlighting chemodynamic relationships influencing galaxy evolution.

Findings

WLM's mean metallicity is [Fe/H] = -1.28 with a spread of 0.38 dex.

WLM exhibits a flat radial metallicity gradient of -0.04 dex per core radius.

Dwarf irregulars have flatter metallicity gradients than dwarf spheroidals, suggesting a link with angular momentum.

Abstract

Building on our previous spectroscopic and photometric analysis of the isolated Local Group dwarf irregular (dIrr) galaxy WLM, we present a comparison of the metallicities of its RGB stars with respect to the well studied Local Group dwarf spheroidal galaxies (dSphs) and Magellanic Clouds. We calculate a mean metallicity of [Fe/H]$ = -1.28 \pm 0.02$, and intrinsic spread in metallicity of $\sigma = 0.38 \pm 0.04$ dex, similar to the mean and spread observed in the massive dSph Fornax and the Small Magellanic Cloud. Thus, despite its isolated environment the global metallicity still follows expectations for WLM's mass and its global chemical evolution is similar to other nearby luminous dwarf galaxies (gas-rich or gas-poor). The data also show a radial gradient in [Fe/H] of $\rm{d[Fe/H]/dr_{c}} = -0.04 \pm 0.04$ dex $\rm{r_{c}^{-1}}$, which is flatter than that seen in the unbiased and spatially extended surveys of dSphs. Comparison of the spatial distribution of [Fe/H] in WLM, the Magellanic Clouds, and a sample of Local Group dSphs, shows an apparent dichotomy in the sense that the dIrrs have statistically flatter radial [Fe/H] gradients than the low angular momentum dSphs. The correlation between angular momentum and radial metallicity gradient is further supported when considering the Local Group dEs. This chemodynamic relationship offers a new and useful constraint for environment driven dwarf galaxy evolution models in the Local Group.