Dr. Ricardo Piorno Schiavon
University of Virginia

University of Florida Astronomy Colloquium - Nov 2nd, 2005

Stellar Population Synthesis in the Blue, from Galactic Clusters, through Nearby Galaxies, to the Distant Universe

Stellar population synthesis provides us with the only possible means to discern the stellar content of distant, unresolved galaxies. Perusal of the recent literature on the field, even by a non-expert, reveals two pieces of common sense: 1) There is general agreement, at least in principle, that any application of stellar population synthesis models to unresolved systems should be preceded by extensive testing against local, resolved, and better-understood templates, such as Galactic clusters; 2) Stellar population synthesis models are plagued by substantial uncertainties, mostly due to calibration difficulties and to innate degeneracies in the response of the observables to fundamental stellar parameters. In this talk I will present my stellar population synthesis models and will describe the efforts that I and my collaborators have spent in the last few years to better understand the complexities inherent to an accurate modelling of stellar population spectra. Strong emphasis will be put on the blue spectral region, due to its importance for distant galaxy work. I will discuss why the use of globular clusters as benchmarks for stellar population synthesis models has turned out to be far more complicated a problem than initially thought. I will show that painstaking calibration efforts and resort to a wide base line can significantly ameliorate the model uncertainties and degeneracies. To end on a further optimistic note, I will show promising results from an application of my models to estimate the mean light-weighted ages and metal abundances of stars in galaxies at z ~ 1, as a part of the DEEP collaboration (see http://deep.ucolick.org/).