Optimal metallicity diagnostics for MUSE observations of low-z galaxies

Bethan Easeman, Patricia Schady, Stijn Wuyts, Robert M Yates

Research output: Contribution to journalArticlepeer-review

2 Citations (SciVal)

Abstract

The relatively red wavelength range (4800-9300 Å) of the VLT Multi Unit Spectroscopic Explorer (MUSE) limits which metallicity diagnostics can be used; in particular excluding those requiring the []λλ3726,29 doublet. We assess various strong line diagnostics by comparing to sulphur -based metallicity measurements for a sample of 671 H ii regions from 36 nearby galaxies from the MUSE Atlas of Disks (MAD) survey. We find that the O3N2 and N2 diagnostics return a narrower range of metallicities that lie up to ∼0.3 dex below -based measurements, with a clear dependence on both metallicity and ionization parameter. The N2S2H α diagnostic shows a near-linear relation with the -based metallicities, although with a systematic downward offset of ∼0.2 dex, but no clear dependence on ionization parameter. These results imply that the N2S2H α diagnostic produces the most reliable results when studying the distribution of metals within galaxies with MUSE. On sub-H ii region scales, the O3N2 and N2 diagnostics measure metallicity decreasing towards the centres of H ii regions, contrary to expectations. The S-calibration and N2S2H α diagnostics show no evidence of this, and show a positive relationship between ionization parameter and metallicity at > 8.4, implying the relationship between ionization parameter and metallicity differs on local and global scales. We also present hiidentify, a python tool developed to identify H ii regions within galaxies from H α emission maps. All segmentation maps and measured emission line strengths for the 4408 H ii regions identified within the MAD sample are available to download.

Original languageEnglish
Pages (from-to)5484-5502
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Volume527
Issue number3
Early online date14 Nov 2023
DOIs
Publication statusPublished - 1 Jan 2024

Acknowledgements

The authors would like to thank Ángeles Díaz for an interesting and enlightening conversation surrounding the use of sulphur T e -based metallicity diagnostics, and the S/O ratio. We also thank Dr Julian Stirling for his guidance on publishing HIIDENTIFY , and the referee for their feedback.

Keywords

  • H ii regions
  • ISM: abundances
  • galaxies: abundances

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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