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

• DOI: 10.1093/mnras/stw3308
• Publication Date: 2016-12-19T20:05:54Z
• Authors: Kai Zhang; Renbin Yan; Kevin Bundy; Matthew Bershady; L. Matthew Haffner; René Walterbos; Roberto Maiolino; Christy Tremonti; Daniel Thomas; Niv Drory; Amy Jones; Francesco Belfiore; Sebastian F. Sánchez; Aleksandar M. Dia...; Dmitry Bizyaev; Christian Nitschelm; Brett Andrews; Jon Brinkmann; Joel R. Brownstein; Edmond Cheung; Cheng Li; David R. Law; Alexandre Roman L...; Daniel Oravetz; Kaike Pan; Thaisa Storchi Be...; Audrey Simmons
• Keywords: Line (geometry); Doubly ionized oxygen

Diffuse ionized gas (DIG) is prevalent in star-forming galaxies. Using a sample of 365 nearly face-on galaxies observed by Mapping Nearby Galaxies at APO, we demonstrate how DIG impacts the measurements emission-line ratios, hence interpretation diagnostic diagrams and gas-phase metallicity measurements. At fixed metallicity, DIG-dominated low ΣHα regions display enhanced [S ii]/Hα, [N [O ii]/Hβ i]/Hα. The gradients these line ratios are determined ΣHα. In ratio diagrams, contamination moves H ii towards composite or low-ionization nuclear region (LI(N)ER)-like regions. A harder ionizing spectrum needed to explain ratios. Leaky models can only shift slightly relative models, thus fail composite/LI(N)ER displayed DIG. Our result favours ionization evolved stars as major source for with LI(N)ER-like emission. significantly bias measurement derived using strong-line methods. Metallicities N2O2 optimal because they exhibit smallest error. O3N2, R23, N2 = ii]/Hα N2S2Hα derive metallicities introduces large gradient itself. method Blanc et al. (IZI hereafter) cannot be applied get an accurate it currently contains that describe