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|Title:||SDSS-IV MaNGA: the impact of diffuse ionized gas on emission-line ratios, interpretation of diagnostic diagrams and gas metallicity measurements||Authors:||Zhang, Kai
Haffner, L. Matthew
BELFIORE, FRANCESCO MICHEL CONCETTO
Sánchez, Sebastian F.
Diamond-Stanic, Aleksandar M.
Brownstein, Joel R.
Law, David R.
Roman Lopes, Alexandre
Storchi Bergmann, Thaisa
|Issue Date:||2017||Journal:||MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY||Number:||466||Issue:||3||First Page:||3217||Abstract:||Diffuse ionized gas (DIG) is prevalent in star-forming galaxies. Using a sample of 365 nearly face-on star-forming galaxies observed by Mapping Nearby Galaxies at APO, 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 Σ<SUB>Hα</SUB> regions display enhanced [S II]/Hα, [N II]/Hα, [O II]/Hβ and [O I]/Hα. The gradients in these line ratios are determined by metallicity gradients and Σ<SUB>Hα</SUB>. In line ratio diagnostic diagrams, contamination by DIG moves H II regions towards composite or low-ionization nuclear emission-line region (LI(N)ER)-like regions. A harder ionizing spectrum is needed to explain DIG line ratios. Leaky H II region models can only shift line ratios slightly relative to H II region models, and thus fail to explain the composite/LI(N)ER line ratios displayed by DIG. Our result favours 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, R<SUB>23</SUB>, N2 = [N II]/Hα and N2S2Hα to derive metallicities introduces bias in the derived metallicity gradients as large as the gradient itself. The strong-line method of Blanc et al. (IZI hereafter) cannot be applied to DIG to get an accurate metallicity because it currently contains only H II region models that fail to describe the DIG.||URI:||http://hdl.handle.net/20.500.12386/29762||URL:||https://academic.oup.com/mnras/article/466/3/3217/2726592||ISSN:||0035-8711||DOI:||10.1093/mnras/stw3308||Bibcode ADS:||2017MNRAS.466.3217Z||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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checked on Jan 18, 2022
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