Studies On The Methodology For Galaxy Physical Parameter Estimation

We use the single stellar population of Bruzual & Charlot (2003) to generate a library of model spectra with a broad range of star forming histories (SFHs), metallicities, dust extinctions and stellar velocity dispersion. The principle component analysis method (PCA) is run on this library to identify its principle components over the rest-frame wavelength range 3700～5500A. We demonstrate that linear combinations of these components can recover information equivalent to traditional spectral indices such as the 4000A break strength and HδA.In addition, the method is able to recover physical parameters such as stellar mass-to-light ratio, star formation rate and dust extinction. We examine in detail the sensitivity of our output galaxy physical parameters to the distribution of the input parameters in our model library as well as the signal-to-noise ratio of the observed spectra in detail. One is the effect of different prior distribution of τv on calculating galaxy parameters. We build model libraries with different prior distribution of τv to calculate galaxy parameters and find distribution of output τv deviate from input when the prior distribution of τv is Gaussian. The other one is the effect of observations’ signal-to-noise ratio (SNR) on calculating galaxy parameters. We obtained the relationship between dispersion of SFR/M*, M*/Lz, τV and SNR respectively by the derived parameters of simulated galaxies which are assigned with different level of noise. Finally, we compare the derived τV of galaxies in SDSS DR7 and with the former theoretical result. We find τv calculated by continuum and absorption line is about 0.5dex smaller thanτV calculated by nebulae emission line systematically. The reason is τV calculated by nebulae emission line stand for τV in star forming region of galaxy and τV calculated by continuum and absorption line is produced by interstellar medium that is outside of star forming region.