The Star Formation Histories of Galaxies: A tour through the STARLIGHT-SDSS database

Abstract

Retrieving the Star Formation History (SFH) of a galaxy out of its integrated spectrum is the central goal of stellar population synthesis. Recent advances in evolutionary synthesis models have given new breath to this old field of research. Modern spectral synthesis techniques incorporating these advances now allow the fitting of galaxy spectra on an Å-by-Å. These detailed fits are useful for a number of studies, like emission line, stellar kinematics, and specially galaxy evolution. Applications of this semi-empirical approach to mega data sets are teaching us a lot about the lives of galaxies. The STARLIGHT spectral synthesis code is one of the tools which allows one to harness this favorable combination of plentifulness of data and models. To illustrate this, we show how SFHs vary across classical emission line diagnostic diagrams. Systematic trends are present along both the star-forming and active-galaxy sequences. We also briefly describe experiments with new versions of evolutionary synthesis models. Last but not least, we announce the public availability of both STARLIGHT and a database of detailed spectral fits and related products for over half a million galaxies from the SDSS. This facility allows more physically inspired explorations of the parameter space than is possible in terms of raw observed properties, offering new ways to navigate through the realm of galaxies.

Resumen

Recuperar la SFH de una galaxia a partir de su espectro integrado es el objetivo central de la síntesis de poblaciones estelares. Recientes avances en los modelos de síntesis evolutiva han dado un nuevo aliento a este campo de investigación, permitiendo el ajuste del espectro de una galaxia ̊A-por- ̊A. Estos ajustes detallados sonútiles para estudios de líneas de emisión, cinemática estelar y evolución de galaxias. El código de síntesis espectral STARLIGHT es una herramienta que permite explotar esta combinación favorable de datos y modelos. A manera de ilustración, mostramos como la SFH varía para galaxias en distintas regiones de un diagrama de diagnóstico clásico. Se detectan fuertes tendencias sistemáticas a lo largo de las secuencias de formación estelar y galaxias activas. Se describen brevemente eperimentos realizados con nuevas versiones de modelos de síntesis.