Local anti-correlation between star-formation rate and gas-phase metallicity in disk galaxies

TL;DR

This study finds a local anti-correlation between star formation rate and gas-phase metallicity in disk galaxies, suggesting external metal-poor gas inflow or outflows influence galaxy evolution.

Contribution

It provides observational evidence of a spaxel-to-spaxel anti-correlation between metallicity and SFR in dwarf galaxies, supporting models of gas inflow or outflow effects.

Findings

Anti-correlation observed between N2 index and Halpha flux.

External metal-poor gas likely fuels star formation.

Metallicity variations and radial gradients do not explain the anti-correlation.

Abstract

Using a representative sample of 14 star-forming dwarf galaxies in the local Universe, we show the existence of a spaxel-to-spaxel anti-correlation between the index N2 (log([NII]6583/Halpha)) and the Halpha flux. These two quantities are commonly employed as proxies for gas-phase metallicity and star formation rate (SFR), respectively. Thus, the observed N2 to Halpha relation may reflect the existence of an anti-correlation between the metallicity of the gas forming stars and the SFR it induces. Such an anti-correlation is to be expected if variable external metal-poor gas fuels the star-formation process. Alternatively, it can result from the contamination of the star-forming gas by stellar winds and SNe, provided that intense outflows drive most of the metals out of the star-forming regions. We also explore the possibility that the observed anti-correlation is due to variations in the physical conditions of the emitting gas, other than metallicity. Using alternative methods to compute metallicity, as well as previous observations of HII regions and photoionization models, we conclude that this possibility is unlikely. The radial gradient of metallicity characterizing disk galaxies does not produce the correlation either.