EXTRAGALACTIC CHEMICAL ABUNDANCES: DO H ii REGIONS AND YOUNG STARS TELL THE SAME STORY? THE CASE OF THE SPIRAL GALAXY NGC 300

By F. Bresolin, W. Gieren, R. Kudritzki, G. Pietrzyński, M. Urbaneja, G. Carraro. 2009

188 citations recorded by the source corpus.

We have obtained new spectrophotometric data for 28 H ii regions in the spiral galaxy NGC 300, a member of the nearby Sculptor Group. The detection of several auroral lines, including [O iii] λ4363, [S iii] λ6312, and [N ii] λ5755, has allowed us to measure electron temperatures and direct chemical abundances for the whole sample. We determine for the first time in this galaxy a radial gas-phase oxygen abundance gradient based solely on auroral lines, and obtain the following least-square solution: 12 + log(O/H) = 8.57(±0.02) − 0.41(±0.03)R/R25, where the galactocentric distance is expressed in terms of the isophotal radius R25. The characteristic oxygen abundance, measured at 0.4 × R25, is 12 + log(O/H) = 8.41. The gradient corresponds to −0.077 ± 0.006 dex kpc−1, and agrees very well with the galactocentric trend in metallicity obtained for 29 B and A supergiants in the same galaxy, −0.081 ± 0.011 dex kpc−1. The intercept of the regression for the nebular data virtually coincides with the intercept obtained from the stellar data, which is 8.59(±0.05). This allows little room for depletion of nebular oxygen onto dust grains, although in this kind of comparison we are somewhat limited by systematic uncertainties, such as those related to the atomic parameters used to derive the chemical compositions. We discuss the implications of our result with regard to strong-line abundance indicators commonly used to estimate the chemical compositions of star-forming galaxies, such as R23. By applying a few popular calibrations of these indices based on grids of photoionization models on the NGC 300 H ii region fluxes, we find metallicities that are higher by 0.3 dex (a factor of 2) or more relative to our nebular (Te based) and stellar ones. We detect Wolf–Rayet stellar emission features in ∼1/3 of our H ii region spectra, and find that in one of the nebulae hosting these hot stars the ionizing field has a particularly hard spectrum, as gauged by the “softness” parameter η = (O+/O++)/(S+/S++). We suggest that this is related to the presence of an early WN star. By considering a larger sample of extragalactic H ii regions we confirm, using direct abundance measurements, previous findings of a metallicity dependence of η, in the sense that softer stellar continua are found at high metallicity.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

THE MASS–METALLICITY RELATION WITH THE DIRECT METHOD ON STACKED SPECTRA OF SDSS GALAXIES (2012, background): “Because the strength of the auroral lines, especially [O iii] λ4363, is a 4 The original data can be found in Bresolin et al. (2004, 2005, 2009a, 2009b), Bresolin (2007), Campbell et al. (1986), Castellanos et al. (2002), de Blok & van der Hulst (1998), Esteban et al. (2009), Fierro et al. (1986),…”
GAS-PHASE OXYGEN GRADIENTS IN STRONGLY INTERACTING GALAXIES. I. EARLY-STAGE INTERACTIONS (2010, unknown): “Some calibrations (including both strong- and weak-line ones) may yield shallower slopes than we calculate (e.g., Kewley & Ellison 2008; Bresolin et al. 2009a).”
Eliminating error in the chemical abundance scale for extragalactic H ii regions (2012, methodology): “This observational result has been also found by Yin et al (2007), Bresolin et al. (2009), Moustakas et al. (2010) and López-Sánchez et al. (2011); in some objects the differences reach up to 0.6 dex.”
DIRECT OXYGEN ABUNDANCES FOR LOW-LUMINOSITY LVL GALAXIES (2012, methodology): “…limited by sample selection effects, potentially making them appropriate for ranking objects on a single scale, but not useful for determining an absolute metallicity as the various methods do not converge (see e.g., Yin et al. 2007; Kewley & Ellison 2008; Bresolin et al. 2009; Berg et al. 2011).”
OPTICAL SPECTROSCOPY AND NEBULAR OXYGEN ABUNDANCES OF THE SPITZER/SINGS GALAXIES (2010, methodology): “Bresolin et al. (2009) performed 21 Note, however, that the metallicities derived from the SDSS 3′′ diameter fiber spectra may be too high by ∼0.1 dex due to aperture bias (Tremonti et al. 2004; Kewley et al. 2005). this experiment by obtaining high-quality electron temperature measurements of 28 H…”
De re metallica: the cosmic chemical evolution of galaxies (2018, methodology): “This has been confirmed both through the direct method applied to individual galactic discs (Bresolin et al., 2009a; Goddard et al., 2011; Bresolin et al., 2012; Sánchez-Menguiano et al., 2017a), as illustrated in Fig.”
THE UNIVERSAL RELATION OF GALACTIC CHEMICAL EVOLUTION: THE ORIGIN OF THE MASS–METALLICITY RELATION (2014, background): “However, longstanding discrepancies between various metallicity diagnostics remain unresolved (e.g., Kudritzki et al. 2008; Bresolin et al. 2009; Kudritzki et al. 2012; Nicholls et al. 2012; Dopita et al. 2013).”
Deriving model-based Te-consistent chemical abundances in ionized gaseous nebulae (2014, result): “Some works point to little difference with CELs (e.g. NGC300, Bresolin et al. 2009), and while some others point to values quite similar to those obtained from RLs (e.g. Simón-Dı́az & Stasińska 2011; Firnstein & Przybilla 2012).”
New calibrations for abundance determinations in H ii regions (2016, methodology): “…by factors of 1.5 to 5 higher than those derived through the directTe method or through empirical calibrations (e.g.,Kennicutt, Bresolin & Garnett 2003; Pilyugin 2003; Kewley & Ellison 2008; Bresolin et al. 2009; Moustakas et al. 2010; López-Sánchez & Esteban 2010; López-Sánchez et al. 2012).”