Empirical Modeling of the Stellar Spectrum of Galaxies

Abstract

An empirical method of modeling the stellar spectrum of galaxies is proposed, based on two successive applications of principal component analysis (PCA). PCA is first applied to the newly available stellar library STELIB, supplemented by the J, H, and K s magnitudes taken mainly from the Two Micron All Sky Survey. Next, the resulting eigenspectra are used to fit the observed spectra of a sample of 1016 galaxies selected from the Sloan Digital Sky Survey Data Release 1 (SDSS DR1). PCA is again applied to the fitted spectra to construct the eigenspectra of galaxies with zero velocity dispersion. The first nine galactic eigenspectra so obtained are then used to model the stellar spectrum of the galaxies in SDSS DR1 and synchronously to estimate the stellar velocity dispersion, the spectral type, the near-infrared spectral energy distribution, and the average reddening. Extensive tests show that the spectra of different types of galaxies can be modeled quite accurately using these eigenspectra. The method can yield stellar velocity dispersion with accuracies better than 10% for the spectra of typical signalto-noise ratios in SDSS DR1.

Ensemble Learning for Independent Component Analysis of Normal Galaxy Spectra

“…This slope is much flatter than that of Calzetti et al (1994), who obtained a value of 0.5. Stellar velocity dispersion.-As in Li et al (2005), the stellar velocity dispersion, Ã , can be given directly by the fit (Fig. 8, top right).…”

Oxygen abundance in the Sloan Digital Sky Survey

“…In this paper we use the method developed by Li et al (2005) to subtract the underlying starlight. Briefly, a set of absorption-line templates with zero velocity dispersion is constructed, on the basis of two successive applications of the technique of Principal Component Analysis (PCA), first to 204 stars in the stellar library STELIB (Le Borgne et al 2003), then to a uniform sample of galaxies selected from SDSS DR1.…”

Spectrum Fitting Code for LAMOST ExtraGAlactic Surveys (LEGAS)

“…Because only few galaxies can be resolved into individual stars, population synthesis method is often used to analyze stellar population of galaxy and to subtract underlying stellar absorption from nebular emission lines. In our Center (Center for astrophysics, USTC), since 1999, we have used and developed different population synthesis methods, which are used to analyze the spectral properties for galaxies (Kong & Cheng 1999;Kong et al 2000, Kong et al 2003, Li et al 2005, Lu et al 2005. In Figure 2, as an example, we show the spectral fitting results for two galaxies in Kong et al (2003).…”

“…Firstly, to reduce the input spectral templates, and then can improve the fitting efficiency, independent component analysis method and principal component analysis method were used recently by Li et al (2005) and Lu et al (2006), respectively. These methods can sufficiently compress the synthetic galaxy spectral library to less then 10 principal components or independent components, which be used as input templates for spectral fitting.…”