The Composition Gradient in M101 Revisited. II. Electron Temperatures and Implications for the Nebular Abundance Scale

By Robert C. Kennicutt Jr., F. Bresolin, D. Garnett. 2003

339 citations recorded by the source corpus.

We use high signal-to-noise ratio spectra of 20 H II regions in the giant spiral galaxy M101 to derive electron temperatures for the H II regions and robust metal abundances over radii R = 0.19-1.25R0 (6-41 kpc). We compare the consistency of electron temperatures measured from the [O III] λ4363, [N II] λ5755, [S III] λ6312, and [O II] λ7325 auroral lines. Temperatures from [O III], [S III], and [N II] are correlated with relative offsets that are consistent with expectations from nebular photoionization models. However, the temperatures derived from the [O II] λ7325 line show a large scatter and are nearly uncorrelated with temperatures derived from other ions. We tentatively attribute this result to observational and physical effects, which may introduce large random and systematic errors into abundances derived solely from [O II] temperatures. Our derived oxygen abundances are well fitted by an exponential distribution over six disk scale lengths, from approximately 1.3 (O/H)☉ in the center to 1/15 (O/H)☉ in the outermost region studied [for solar 12 + log(O/H) = 8.7]. We measure significant radial gradients in N/O and He/H abundance ratios, but relatively constant S/O and Ar/O. Our results are in approximate agreement with previously published abundances studies of M101 based on temperature measurements of a few H II regions. However, our abundances are systematically lower by 0.2-0.5 dex than those derived from the most widely used strong-line "empirical" abundance indicators, again consistent with previous studies based on smaller H II region samples. Independent measurements of the Galactic interstellar oxygen abundance from ultraviolet absorption lines are in good agreement with the Te-based nebular abundances. We suspect that most of the disagreement with the strong-line abundances arises from uncertainties in the nebular models that are used to calibrate the "empirical" scale, and that strong-line abundances derived for H II regions and emission-line galaxies are as much as a factor of 2 higher than the actual oxygen abundances. However, other explanations, such as the effects of temperature fluctuations on the auroral line based abundances, cannot be completely ruled out. These results point to the need for direct abundance determinations of a larger sample of extragalactic H II regions, especially for objects more metal-rich than solar.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/bb9889e2a399caaab156ad102765eca72ef79734

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Atomic and Molecular Physics, and Optics

In Instrumentation

Citations in the corpus

Scaling relations and the fundamental line of the local group dwarf galaxies (2008, background): “They also cite evidence from Kennicutt et al. (2003) that “strong line” methods such as theirs may overestimate the true abundance by as much as a factor of 2.”
A VLT study of metal-rich extragalactic H II regions - I. Observations and empirical abundances (2005, methodology): “19 confirms earlier findings (Pindao et al. 2002; Kennicutt et al. 2003; Bresolin et al. 2004) that indicated how some of the calibrations of statistical methods available in the literature (e.g. Edmunds & Pagel 1984; Zaritsky et al. 1994) can severely overestimate the abundance of metal-rich H …”
A Realistic Determination of the Error on the Primordial Helium Abundance: Steps toward Nonparametric Nebular Helium Abundances (2004, background): “4 Note that Kennicutt et al. (2003) find that [O ii] temperatures are not reliable, but the reason for this may become clearer in the future.”
OPTICAL SPECTROSCOPY AND NEBULAR OXYGEN ABUNDANCES OF THE SPITZER/SINGS GALAXIES (2010, methodology): “…that empirical calibrations 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;…”
Optical Star Formation Rate Indicators (2005, neutral): “…that the theoretical calibration of R23 is discrepant by 0.2–0.5 dex relative to electron-temperature abundance measurements, and may require revision to lower abundances (J. Moustakas et al. 2006b, in preparation; Pilyugin 2001; Kennicutt et al. 2003; Garnett et al. 2004; Bresolin et al. 2004).”
The Effect of Metallicity on Cepheid-based Distances (2004, methodology): “As reflected in the decreased error bar, the results presented in this paper are more robust: the K98 analysis suffered from a lack of galaxies with Z > ZLMC and used an indirect TRGB and Cepheid comparison (via different galaxies in the same group) for two of the metal-rich fields.”
New fully empirical calibrations of strong-line metallicity indicators in star forming galaxies (2016, background): “…of similar temperatures discrepancies have been reported by several works in the literature aimed at studying the physical properties of single Hii regions (see e.g. Kennicutt et al. 2003; Bresolin et al. 2005; Esteban et al. 2009; Pilyugin et al. 2009; Binette et al. 2012; Berg et al. 2015).”
The Mass-Metallicity Relation at z≳2 (2006, methodology): “Using electron temperature measurements to determine ionic abundances in 20 extragalactic H II regions, Kennicutt et al. (2003) find that the nitrogen abundance is adequately described by a simple model with a primary compo- nent with constant log(N/O) = −1.5 and a secondary component for which…”
THEORETICAL EVOLUTION OF OPTICAL STRONG LINES ACROSS COSMIC TIME (2013, methodology): “For nitrogen, we assume primary and secondary nucleosynthetic components as measured by Mouhcine & Lançon (2002) and Kennicutt et al. (2003).”
The luminosity–metallicity relation in the local Universe from the 2dF Galaxy Redshift Survey (2004, methodology): “However, the P-method seems to suffer some weaknesses even within the abundance range for which it was designed for(Saviane et al. 2002; Kennicutt et al. 2003).”
REST-FRAME OPTICAL SPECTRA OF THREE STRONGLY LENSED GALAXIES AT z ∼ 2 (2009, background): “This relationship has a 1σ scatter of 0.05 dex for the sample of star-forming galaxies presented in Tremonti et al. (2004), though this error may underestimate the true systematic uncertainty (Kennicutt et al. 2003).”
Evidence for Solar Metallicities in Massive Star-forming Galaxies at z ≳ 2 (2004, methodology): “Furthermore, in objects for which [O iii] k4363 or other temperature-sensitive auroral lines are detected, metallicities inferred from the upper branch of the R23 calibration are systematically higher by 0.2–0.5 dex than those computed directly from the Te method (Kennicutt et al. 2003).”