SDSS-IV MaNGA : the impact of diffuse ionized gas on emission-line ratios, interpretation of diagnostic diagrams and gas metallicity measurements

By Kai Zhang, R. Yan, K. Bundy, M. Bershady, L. M. Haffner, R. Walterbos, R. Maiolino, Christy A. Tremonti, D. Thomas, N. Drory and 17 more. 2016

146 citations recorded by the source corpus.

Diffuse Ionized Gas (DIG) is prevalent in star-forming galaxies. Using a sample of 365 nearly face-on star-forming galaxies observed by MaNGA, we demonstrate how DIG in star-forming galaxies impacts the measurements of emission line ratios, hence the interpretation of diagnostic diagrams and gas-phase metallicity measurements. At fixed metallicity, DIG-dominated low H\alpha\ surface brightness regions display enhanced [SII]/H\alpha, [NII]/H\alpha, [OII]/H\beta, and [OI]/H\alpha. The gradients in these line ratios are determined by metallicity gradients and H\alpha\ surface brightness. In line ratio diagnostic diagrams, contamination by DIG moves HII regions towards composite or LI(N)ER-like regions. A harder ionizing spectrum is needed to explain DIG line ratios. Leaky HII region models can only shift line ratios slightly relative to HII region models, and thus fail to explain the composite/LI(N)ER line ratios displayed by DIG. Our result favors ionization by evolved stars as a major ionization source for DIG with LI(N)ER-like emission. DIG can significantly bias the measurement of gas metallicity and metallicity gradients derived using strong-line methods. Metallicities derived using N2O2 are optimal because they exhibit the smallest bias and error. Using O3N2, R23, N2=[NII]/H\alpha, and N2S2H\alpha\ (Dopita et al. 2016) to derive metallicities introduces bias in the derived metallicity gradients as large as the gradient itself. The strong-line method of Blanc et al. (2015; IZI hereafter) cannot be applied to DIG to get an accurate metallicity because it currently contains only HII region models which fail to describe the DIG.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/6f9751d4f8fe20f9a416156eb8560aa5a3949b9b

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In Astronomy and Astrophysics

Citations in the corpus

The mass–metallicity and the fundamental metallicity relation revisited on a fully Te-based abundance scale for galaxies (2019, methodology): “…1967; Stasińska 2002, 2005) and/or to the contribution of diffuse gas to line emission when dealing with global galaxy spectra (Sanders et al. 2017; Zhang et al. 2017), the metallicity measurements based on the Te method have proven to be in better agreement with independent measurements of…”
SDSS IV MaNGA – metallicity and nitrogen abundance gradients in local galaxies (2017, background): “Key words: galaxies: ISM – galaxies: evolution – galaxies: fundamental parameters – galaxies: survey”