A Direct Stellar Metallicity Determination in the Disk of the Maser Galaxy NGC 4258

Urbaneja

et al. 2016

ApJ

Self Cite

100

142

We present spectra of 14 A-type supergiants in the metal-rich spiral galaxy M83. We derive stellar parameters and metallicities, and measure a spectroscopic distance modulus µ = 28.47 ± 0.10 (4.9 ± 0.2 Mpc), in agreement with other methods. We use the stellar characteristic metallicity of M83 and other systems to discuss a version of the galaxy mass-metallicity relation that is independent of the analysis of nebular emission lines and the associated systematic uncertainties. We reproduce the radial metallicity gradient of M83, which flattens at large radii, with a chemical evolution model, constraining gas inflow and outflow processes. We carry out a comparative analysis of the metallicities we derive from the stellar spectra and published H II region line fluxes, utilizing both the direct, T ebased method and different strong-line abundance diagnostics. The direct abundances are in relatively good agreement with the stellar metallicities, once we apply a modest correction to the nebular oxygen abundance due to depletion onto dust. Popular empirically calibrated strong-line diagnostics tend to provide nebular abundances that underestimate the stellar metallicities above the solar value by ∼0.2 dex. This result could be related to difficulties in selecting calibration samples at high metallicity. The O3N2 method calibrated by Pettini and Pagel gives the best agreement with our stellar metallicities. We confirm that metal recombination lines yield nebular abundances that agree with the stellar abundances for high metallicity systems, but find evidence that in more metal-poor environments they tend to underestimate the stellar metallicities by a significant amount, opposite to the behavior of the direct method.

Section: Evolutionary Statussupporting

confidence: 91%

Section: A Recommended Strong-line Method?supporting

confidence: 73%

Young Stars and Ionized Nebulae in M83: Comparing Chemical Abundances at High Metallicity

Bresolin

Urbaneja

et al. 2016

ApJ

Self Cite

100

142

“…Correct interpretation of their spectra is made possible by sophisticated model atmospheres, and so such work is free of the systematic effects that hamper studies of H II regions such as unknown temperature structures and large-scale inhomogeneities. A small sample of nearby galaxies has been studied using blue supergiants (BSGs; e.g., Kudritzki et al 2012Kudritzki et al , 2013Kudritzki et al , 2014, and it was shown in the case of NGC 300 that the BSG results were in excellent agreement with those of auroral line H II region measurements (Bresolin et al 2009).…”

Section: Introductionmentioning

confidence: 98%

Red Supergiants as Cosmic Abundance Probes: The Magellanic Clouds

Davies

Gazak

et al. 2015

ApJ

Self Cite

104

Red Supergiants (RSGs) are cool (∼4000 K), highly luminous stars (L 10 5 ∼ L ⊙ ), and are among the brightest near-IR sources in star-forming galaxies. This makes them powerful probes of the properties of their host galaxies, such as kinematics and chemical abundances. We have developed a technique whereby metallicities of RSGs may be extracted from a narrow spectral window around 1 μm from only moderate resolution data. The method is therefore extremely efficient, allowing stars at large distances to be studied, and so has tremendous potential for extragalactic abundance work. Here, we present an abundance study of the Large and Small Magellanic Clouds (LMC and SMC respectively) using samples of 9-10 RSGs in each. We find average abundances for the two galaxies of ). These values are consistent with other studies of young stars in these galaxies, and though our result for the SMC may appear high it is consistent with recent studies of hot stars which find 0.5-0.8 dex below solar. Our best-fit temperatures are on the whole consistent with those from fits to the optical-infrared spectral energy distributions, which is remarkable considering the narrow spectral range being studied. Combined with our recent study of RSGs in the Galactic cluster Per OB1, these results indicate that this technique performs well over a range of metallicities, paving the way for forthcoming studies of more distant galaxies beyond the Local Group.

“…In recent years, this new method has been successfully applied to galaxies out to a distance of 7 Mpc (Urbaneja et al 2008;U et al 2009;Kudritzki et al 2012Kudritzki et al , 2013Kudritzki et al , 2014Hosek et al 2014).…”

Section: Introductionmentioning

confidence: 99%

The flux-weighted gravity-luminosity relationship of blue supergiant stars as a constraint for stellar evolution

Meynet

Georgy

2015

A&A

Self Cite

Context. The flux-weighted gravity-luminosity relationship (FGLR) of blue supergiant stars (BSG) links their absolute magnitude to the spectroscopically determined flux-weighted gravity log g/T 4 eff . BSG are the brightest stars in the universe at visual light and the application of the FGLR has become a powerful tool for determining extragalactic distances. Aims. Observationally, the FGLR is a tight relationship with only small scatter. It is, therefore, ideal for using as a constraint for stellar evolution models. The goal of this work is to investigate whether stellar evolution can reproduce the observed FGLR and to develop an improved foundation for the FGLR as an extragalactic distance indicator. Methods. We used different grids of stellar models for initial masses between 9 and 40 M and for metallicities between Z = 0.002 and 0.014, with and without rotation, which were computed with various mass loss rates during the red supergiant phase. For each of these models, we discuss the details of post-main sequence evolution and construct theoretical FGLRs by means of population synthesis models that we then compare with the observed FGLR. Results. In general, the stellar evolution model FGLRs agree reasonably well with the observed one. There are, however, differences between the models, in particular with regard to the shape and width (scatter) in the flux-weighted gravity-luminosity plane. The best agreement is obtained with models that include the effects of rotation and assume that the large majority, if not all, of the observed BSG evolve toward the red supergiant phase and that only a few are evolving back from this stage. The effects of metallicity on the shape and scatter of the FGLR are small. Conclusions. The shape, scatter, and metallicity dependence of the observed FGLR are explained well by stellar evolution models. This provides a solid theoretical foundation for using this relationship as a robust extragalactic distance indicator.