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Unveiling chemical patterns in galaxies through Bayesian spectral fitting

Grant number: 13/11837-9
Support type:Scholarships in Brazil - Post-Doctorate
Effective date (Start): November 01, 2013
Effective date (End): April 30, 2014
Field of knowledge:Physical Sciences and Mathematics - Astronomy - Extragalactic Astrophysics
Principal Investigator:Paula Rodrigues Teixeira Coelho
Grantee:Jacopo Chevallard
Home Institution: Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG). Universidade de São Paulo (USP). São Paulo , SP, Brazil


The chemical composition of stars in a galaxy encloses valuable information about the past history of star formation and chemical enrichment. This depends on the complex interplay between infall of pristine gas and its consumption by star formation, heavy element production, and the potential ejection of metal-enriched gas from the galaxy, for example by supernova explosions and active galactic nuclei. As these processes depend themselves on local galaxy environment and, on a larger scale, on the way in which baryons assemble in a hierarchical universe, the chemical composition of stellar populations provides important constraints on galaxy evolution scenarios.The most direct way to constrain the chemical composition of stars in external galaxies is to interpret the absorption-line signatures of metals in observed spectra. We have started to develop a new approach to efficiently interpret these signatures, which fully exploits the information available in each spectral pixel. This approach combines a Bayesian analysis of galaxy spectra with a classification and interpretation of the fit residuals. To achieve this, we combine the latest version of the population synthesis code of Bruzual & Charlot (2003) with the models for non-scaled solar abundance ratios of Coelho et al. (2007, 2011). The main two adjustable parameters are the overall metallicity (Z) and the ratio of alpha-elements to iron ([alpha/Fe]). We will use this approach to study the integrated spectra of a carefully selected sample of star clusters in the Galaxy and the Magellanic Clouds, and of galaxies of different spectral types. A PCA-based analysis of the fit residuals will allow us to separate these spectra into different `residual classes', related to different chemical abundance variations. This project will provide new insight into the variation of chemical abundances of stars in galaxies, building the basis for a future, physically motivated development of theoretical models with multiple chemical parameters.

Scientific publications
(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)
CHEVALLARD, JACOPO; CHARLOT, STEPHANE. Modelling and interpreting spectral energy distributions of galaxies with BEAGLE. Monthly Notices of the Royal Astronomical Society, v. 462, n. 2, p. 1415-1443, OCT 21 2016. Web of Science Citations: 43.

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