Recovering physical parameters from galaxy spectra using MOPED

We derive physical parameters of galaxies from their observed spectrum, using MOPED, the optimized data compression algorithm of Heavens, Jimenez & Lahav (2000). Here we concentrate on parametrising galaxy properties, and apply the method to the NGC galaxies in Kennicutt’s spectral atlas. We focus on deriving the star formation history, metallicity and dust content of galaxies. The method is very fast, taking a few seconds of CPU time to estimate ∼ 17 parameters, and so specially suited to study of large data sets, such as the AngloAustralian 2 degree field galaxy survey and the Sloan Digital Sky Survey. Without the power of MOPED, the recovery of star formation histories in these surveys would be impractical. In the Kennicutt atlas, we find that for the spheroidals a small recent burst of star formation is required to provide the best fit to the spectrum. There is clearly a need for theoretical stellar atmospheric models with spectral resolution better than 1Å if we are to extract all the rich information that large redshift surveys contain in their galaxy spectra.