Fake star formation bursts: blue horizontal branch stars masquerade as young stars in optical integrated light spectroscopy - Astrophysics > Cosmology and Nongalactic AstrophysicsReportar como inadecuado




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Abstract: Model color magnitude diagrams of low-metallicity globular clusters usuallyshow a deficit of hot evolved stars with respect to observations. Weinvestigate quantitatively the impact of such modelling inaccuracies on thesignificance of star formation history reconstructions obtained from opticalintegrated spectra. To do so, we analyse the sample of spectra of galacticglobular clusters of Schiavon et al. with STECKMAP Ocvirk et al. and thestellar population models Vazdekis et al. and Bruzual and Charlot, and focus onthe reconstructed stellar age distributions. Firstly, we show thatbackground-foreground contamination correlates with EB-V, which allows us todefine a clean subsample of uncontaminated GCs, on the basis of a EB-Vfiltering.We then identify a -confusion zone- where fake young bursts of star formationpop up in the star formation history although the observed population isgenuinely old. These artifacts appear for 70-100% of cases depending on thepopulation model used, and contribute up to 12% of the light in the optical.Their correlation with the horizontal branch ratio indicates that the confusionis driven by HB morphology: red horizontal branch clusters are well fitted byold stellar population models while those with a blue HB require an additionalhot component. The confusion zone extends over Fe-H=-2,-1.2, although welack the data to probe extreme high and low metallicity regimes. As aconsequence, any young starburst superimposed on an old stellar population inthis metallicity range could be regarded as a modeling artifact, if it weighsless than 12% of the optical light, and if no emission lines typical of an HIIregion are present.



Autor: P. Ocvirk

Fuente: https://arxiv.org/







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