Planetary nebulae: the universal mass-metallicity relation for Local Group dwarf galaxies and the chemistry of NGC 205

TL;DR

This study analyzes planetary nebulae in NGC 205 to establish a universal mass-metallicity relation for Local Group dwarf galaxies, revealing consistent chemical evolution patterns across different galaxy types and with star-forming galaxies.

Contribution

It provides the first robust planetary nebulae-based mass-metallicity relation for Local Group dwarf galaxies, demonstrating a universal trend across galaxy types and aligning with stellar metallicity measurements.

Findings

PN metallicity trends are consistent across dwarf galaxy types.

The derived MZR aligns with stellar metallicity-based relations.

The MZR extends to star-forming galaxies, indicating universality.

Abstract

Here we study 16 planetary nebulae (PNe) in the dwarf irregular galaxy NGC 205 by using GMOS@Gemini spectra to derive their physical and chemical parameters. The chemical patterns and evolutionary tracks for 14 of our PNe suggest that there are no type I PNe among them. These PNe have an average oxygen abundance of 12+log(O/H)=8.08$\pm$0.28, progenitor masses of 2-2.5M$_{\odot}$ and thus were born ~1.0-1.7Gyr ago. Our results are in good agreement with previous PN studies in NGC 205. The present 12+log(O/H) is combined with our previous works and with the literature to study the PN metallicity trends of the Local Group (LG) dwarf galaxies, in an effort to establish the PN luminosity- and mass-metallicity relations (LZR and MZR) for the LG dwarf irregulars (dIrrs) and dwarf spheroidals (dSphs). Previous attempts to obtain such relations failed to provide correct conclusions because were based on limited samples (Richer & McCall 1995; Gon\c{c}calves et al. 2007). As far as we are able to compare stellar with nebular metallicities, our MZR is in very good agreement with the slope of the MZR recently obtained for LG dwarf galaxies using spectroscopic stellar metallicities (Kirby et al. 2013). Actually, we found that both dIrr and dSph galaxies follow the same MZR, at variance with the differences claimed in the past. Moreover our MZR is also consistent with the global MZR of star-forming galaxies, which span a wider stellar mass range ($\sim10^6$ - $\sim10^{11}$M$\odot$).