On the relationship between auroral and nebular oxygen line intensities in spectra of H II regions

Abstract

Abstract. We investigate relationships between observed auroral and nebular oxygen line fluxes in spectra of H  regions. We find a relation that is metallicity-dependent at low metallicities, but becomes independent of metallicity (within the uncertainties of the available data) above 12+logO/H ∼ 8.25, i.e. there is one-to-one correspondence (the ff-relation) between auroral and nebular oxygen line fluxes in spectra of high-metallicity H  regions. The ff-relation allows one to estimate the flux in the auroral line from strong oxygen line measurements only. This solves the problem of the electron temperature (and, consequently, abundance) determination in high-metallicity H  regions. The ff-relation confirms the basic idea of the "empirical" method, proposed by Pagel et al. (1979, MNRAS, 189, 95) a quarter of a century ago, that the oxygen abundance in H  region can be esimated from the strong oxygen lines measurements only.

PPAK Wide-field Integral Field Spectroscopy of NGC 628 - I. The largest spectroscopic mosaic on a single galaxy★

“…The last strong‐line empirical method considered is a combination of the flux–flux (or ff‐relation) found by Pilyugin (2005) and parametrized by Pilyugin, Thuan & Vílchez (2006), the t 2 − t 3 relation between the O + and O ++ zones electron temperatures for high‐metallicity regions proposed by Pilyugin (2007) and an updated version of the T e ‐based method for metallicity determination (Izotov et al 2006). According to these authors, the combination of these methods solves the problem of the determination of the electron temperatures in high‐metallicity H ii regions, where faint auroral lines are not detected.…”

PPAK wide-field Integral Field Spectroscopy of NGC 628 - II. Emission line abundance analysis★

“…The reddening‐corrected line ratios for both the fibre‐by‐fibre and H ii region catalogues were used to derived the oxygen abundance for each individual spectrum, using a subset of the abundance diagnostics employed in Paper I. Different abundance estimators were used in order to explore the effects of a particular calibration depending on the physical properties of the galaxy; 4 they correspond to a R 23 ‐based calibrator (Kobulnicky & Kewley 2004, hereafter KK04), an ‘index‐empirical’ method after Pettini & Pagel (2004) (hereafter PP04), and two additional strong‐line empirical methods proposed by Pilyugin (2005) and Pilyugin (2007).…”

“…The third considered calibrator is the ff– T e method, i.e. the combination of the flux–flux (or ff relation) proposed by Pilyugin (2005), and an updated version of the T e ‐based method for metallicity determination (Izotov et al 2006). The ff relation links the flux of the auroral line [O iii ]λ4363 to the total flux in the strong nebular lines [O ii ]λ3727 and [O iii ]λ4959, λ5007.…”

On the electron temperature determination in high-metallicity H II regions

“…If this is the case, then one can expect that the diagnostic line ratios can be expressed in terms of the intensities of the oxygen nebular lines. Indeed, it has been found empirically that there is a relationship (the ff relation) between auroral [O iii ]λ4363 and nebular oxygen line intensities in spectra of H ii regions (Pilyugin 2005; Pilyugin, Thuan & Vílchez 2006a). In other words, the diagnostic line ratio Q O iii , used for the determination of the electron temperature within the [O iii ] zone, can be expressed in terms of the nebular oxygen line intensities.…”