Gas metallicity diagnostics in star-forming galaxies

By Tohru Nagao, R. Maiolino, Alessandro Marconi Arcetri Observatory, National Space Development Agency of Japan. 2006

294 citations recorded by the source corpus.

Generally the gas metallicity in distant galaxies can only be inferred by using a few prominent emission lines. Various theoretical models have been used to predict the relationship between emission line fluxes and metallicity, suggesting that some line ratios can be used as diagnostics of the gas metallicity in galaxies. However, accurate empirical calibrations of these emission line flux ratios from real galaxy spectra spanning a wide metallicity range are still lacking. In this paper we provide such empirical calibrations by using the combination of two sets of spectroscopic data: one consisting of low-metallicity galaxies with a measurement of [Oiii] λ 4363 taken from the literature, including spectra from the Sloan Digital Sky Survey (SDSS), and the other one consisting of galaxies in the SDSS database whose gas metallicity has been determined from various strong emission lines in their spectra. This combined data set constitutes the largest sample of galaxies with information on the gas metallicity available so far and spanning the widest metallicity range. By using these data we obtain accurate empirical relations between gas metallicity and several emission line diagnostics, including the R 23 parameter, the [Nii] λ 6584/H α and [Oiii] λ 5007/[Nii] λ 6584 ratios. Our empirical diagrams show that the line ratio [Oiii] λ 5007/[Oii] λ 3727 is a useful tool to break the degeneracy in the R 23 parameter when no information on the [Nii] λ 6584 line is available. The line ratio [Neiii] λ 3869/[Oii] λ 3727 also results to be a useful metallicity indicator for high- z galaxies, especially when the R 23 parameter or other diagnostics involving [Oiii] λ 5007 or [Nii] λ 6584 are not available. Additional, useful diagnostics newly proposed in this paper are the line ratios of (H α +[Nii]$\lambda\lambda$6548,6584)/[Sii] λ 6720, [Oiii] λ 5007/H β , and [Oii] λ 3727/H β . Finally, we compare these empirical relations with photoionization models. We find that the empirical R 23 -metallicity sequence is strongly discrepant with respect to the trend expected by models with constant ionization parameter. Such a discrepancy is also found for other line ratios. These discrepancies provide evidence for a strong metallicity dependence of the average ionization parameter in galaxies. In particular, we find that the average ionization parameter in galaxies increases by ~0.7 dex as the metallicity decreases from 2 $Z_{\odot}$ to 0.05 $Z_{\odot}$, with a small dispersion. This result should warn about the use of theoretical models with constant ionization parameter to infer metallicities from observed line ratios.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/e55cb1e49742aa92735e6d069b075bc3bb4ef935

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Citations in the corpus

Modelling the nebular emission from primeval to present-day star-forming galaxies (2016, methodology): “…active galactic nucleus (AGN) in a galaxy are routinely used as global diagnostics of gas metallicity and excitation, dust content, star formation rate and nuclear activity (e.g., Izotov & Thuan 1999; Kobulnicky et al. 1999; Kauffmann et al. 2003; Nagao et al. 2006b; Kewley & Ellison 2008).”
New fully empirical calibrations of strong-line metallicity indicators in star forming galaxies (2016, methodology): “Moreover, their ratio [Oiii]/[Oii] is sensitive to the ionization parameter and it is also used as an indicator of oxygen abundance, especially in metal enriched galaxies, due to the physical link between ionization and gas-phase metallicity (e.g. Nagao et al. 2006; Masters et al. 2016).”
Measuring Black Hole Spin Using X-Ray Reflection Spectroscopy (2013, background): “In a free-fit, the spectral analysis of NGC 3783 clearly demands iron abundances that are 2–4× the cosmic average, in line with the metallicity enhancement often inferred within Seyfert nuclei on the basis of the optical/UV line ratios (e.g., Warner et al. 2004; Nagao et al. 2006).”
The relation between metallicity, stellar mass and star formation in galaxies: an analysis of observational and model data (2011, result): “Secondly, Nagao et al. (2006) have already pointed out that their metallicity derivation method – which uses the same calibration sample as Maiolino et al. (2008) – may overestimate the gas metallicity at Z > 9.0 by a factor of ∼0.1 dex compared to the Tremonti et al. (2004) method.”
Metallicity Calibrations and the Mass-Metallicity Relation for Star-forming Galaxies (2008, methodology): “Initial investigations into the extent of these discrepancies have recently been made by Liang et al. (2006); Yin et al. (2007b,a), and Nagao et al. (2006).”
Rest-frame ultraviolet-to-optical spectral characteristics of extremely metal-poor and metal-free galaxies (2011, background): “Indeed, Nagao et al. (2006) suggest Z dependence of U to explain their empirical relations.”
EXTRAGALACTIC CHEMICAL ABUNDANCES: DO H ii REGIONS AND YOUNG STARS TELL THE SAME STORY? THE CASE OF THE SPIRAL GALAXY NGC 300 (2009, methodology): “…methods for H II regions have already been carried out by several authors, and we refer the reader to the raher vast recent literature on the subject (Kennicutt et al. 2003; Pérez-Montero & Díaz 2005; Nagao et al. 2006; Yin et al. 2007; Liang et al. 2007; Shi et al. 2007; Kewley & Ellison 2008).”
Ionization state of inter-stellar medium in galaxies: evolution, SFR-M * -Z dependence, and ionizing photon escape (2013, methodology): “…(2014) Downloaded from https://academic.oup.com/mnras/article-abstract/442/1/900/1252695 by guest on 28 July 2018 temperature Te method, and (ii) 22 482 star-forming SDSS galaxies with 12 + log (O/H) > 8.2 given with the photoionization model (Kewley & Dopita 2002; see also Nagao et al. 2006).”
An extreme [O III] emitter at z = 3.2: a low metallicity Lyman continuum source (2015, background): “This line is detected in all AGN types studied in Nagao et al. (2006).”
JWST Census for the Mass–Metallicity Star Formation Relations at z = 4–10 with Self-consistent Flux Calibration and Proper Metallicity Calibrators (2023, methodology): “…Figure 7, we examine the following ﬁ ve popular metallicity indicators: Ne3O2 ) , as well as R23 and O32 by comparing with the empirical indicators proposed by Maiolino et al. ( 2008; see also Nagao et al. 2006 ) , Curti et al. ( 2017, 2020 ) , Bian et al. ( 2018 ) , and Nakajima et al. ( 2022 ) .”
GRB hosts through cosmic time - VLT/X-Shooter emission-line spectroscopy of 96 γ-ray-burst-selected galaxies at 0.1 (2015, background): “Given the aforementioned constraints, we decide to base our metallicity measurements on the single set of calibrators from Nagao et al. (2006) and Maiolino et al. (2008), which provide a homogeneous set of line diagnostics for different line ratios.”
SDSS IV MaNGA – spatially resolved diagnostic diagrams: a proof that many galaxies are LIERs (2016, background): “…of this branch can be reproduced well by HII regions photoionisation models as the envelope of the expected line ratios for different values of metallicity and ionisation parameter for gas ionised by OB stars (Kewley et al. 2001; Nagao et al. 2006; Stasińska et al. 2006; Sánchez et al. 2015).”
LSD: Lyman-break galaxies Stellar populations and Dynamics – I. Mass, metallicity and gas at z∼ 3.1 (2009, methodology): “Gas-phase metallicities were derived by comparing the observed line ratios with the calibrations in Nagao et al. (2006) and Maiolino et al. (2008).”
OPTICAL SPECTROSCOPY AND NEBULAR OXYGEN ABUNDANCES OF THE SPITZER/SINGS GALAXIES (2010, methodology): “…generally yield oxygen abundances that are factors of 1.5–5 lower than abundances derived using theoretical calibrations (Kennicutt et al. 2003a; Garnett et al. 2004b; Bresolin et al. 2004, 2005; Shi et al. 2006; Nagao et al. 2006; Liang et al. 2006; Yin et al. 2007; Kewley & Ellison 2008).”
THE MOSDEF SURVEY: EXCITATION PROPERTIES OF z ∼ 2.3 STAR-FORMING GALAXIES (2014, background): “Nakajima et al. (2013) find that the sample of low-metallicity galaxies in SDSS with direct oxygen abundance estimates from Nagao et al. (2006) populate this same region of O32R23 parameter space.”
THE SPECTRAL EVOLUTION OF THE FIRST GALAXIES. I. JAMES WEBB SPACE TELESCOPE DETECTION LIMITS AND COLOR CRITERIA FOR POPULATION III GALAXIES (2011, background): “5 Myr) populations with high metallicities also display very weak [OIII] emission lines (e.g. Panagia 2003; Nagao et al. 2006).”