Joey Richards

Statistics Department, Carnegie Mellon University

Accurate Parameter Estimation for Star Formation History in Galaxies

Astrostatistics Seminar, Friday, March 20, 2009
1:30 PM, Baker Hall 232Q, CMU

Abstract:

The physics of star formation in galaxies is complicated and poorly understood. To further our knowledge of these physical processes, it is essential that we characterize the formation and evolution of millions of galaxies. The spectral synthesis STARLIGHT code of Cid Fernandes et al. (2001) was designed for this purpose. Results of STARLIGHT are highly dependent on the choice of input basis of simple stellar population (SSP) spectra. Speed of the code, which uses Markov Chain Monte Carlo methods, scales as the square of the number of basis spectra, making it computationally necessary to choose a small number of SSPs on a course grid of age and metallicity. In this talk, we develop methods based on diffusion map (Lafon & Lee, 2006) that, for the first time, choose appropriate bases of prototype SSP spectra from a large set of SSP spectra meant to approximate the continuous grid of age and metallicity of SSP's of which galaxies are truly composed. We show that our techniques achieve better accuracy of physical parameter estimation for both simulated and real galaxies. Specifically, we show that our methods significantly decrease the age-metallicity degeneracity that is common in galaxy population synthesis methods.