Stellar population synthesis at the resolution of 2003

TL;DR

Bruzual and Charlot (2003) develop a high-resolution stellar population synthesis model that computes spectral evolution from 100,000 years to 20 Gyr at 3 Å resolution over 3200–9500 Å (and broader, lower-resolution coverage to 160 μm). By integrating a flexible set of stellar evolution tracks with a multi-library spectral database (BaSeL, STELIB, Pickles) and a careful TP-AGB treatment, the model reproduces color-magnitude diagrams of Galactic clusters, the integrated colors of Magellanic clusters under stochastic sampling, and detailed SDSS EDR galaxy spectra including absorption-line indices. It enables robust SFH, metallicity, and dust inferences from spectral fits (via MOPED) and identifies composite indices (eg MgFe') that are largely insensitive to abundance ratio variations. The work provides a practical, high-fidelity tool for interpreting large spectroscopic surveys and for breaking age-metallicity degeneracies in galaxies across all ages.

Abstract

We present a new model for computing the spectral evolution of stellar populations at ages between 100,000 yr and 20 Gyr at a resolution of 3 A across the whole wavelength range from 3200 to 9500 A for a wide range of metallicities. These predictions are based on a newly available library of observed stellar spectra. We also compute the spectral evolution across a larger wavelength range, from 91 A to 160 micron, at lower resolution. The model incorporates recent progress in stellar evolution theory and an observationally motivated prescription for thermally-pulsing stars on the asymptotic giant branch. The latter is supported by observations of surface brightness fluctuations in nearby stellar populations. We show that this model reproduces well the observed optical and near-infrared colour-magnitude diagrams of Galactic star clusters of various ages and metallicities. Stochastic fluctuations in the numbers of stars in different evolutionary phases can account for the full range of observed integrated colours of star clusters in the Magellanic Clouds. The model reproduces in detail typical galaxy spectra from the Early Data Release (EDR) of the Sloan Digital Sky Survey (SDSS). We exemplify how this type of spectral fit can constrain physical parameters such as the star formation history, metallicity and dust content of galaxies. Our model is the first to enable accurate studies of absorption-line strengths in galaxies containing stars over the full range of ages. Using the highest-quality spectra of the SDSS EDR, we show that this model can reproduce simultaneously the observed strengths of those Lick indices that do not depend strongly on element abundance ratios [abridged].

Figures (22)

• Figure 1: Evolution of the $B\!-\!V$ and $V\!-\!K$ colours and stellar mass-to-light ratio $M/L_V$ of simple stellar populations for different metallicities, $Z=0.004$ (dotted line), $Z=Z_{\sun}=0.02$ (solid line) and $Z=0.05$ (dashed line), for the standard model of Section 3. All models have the 2003PASPchab IMF truncated at $0.1\,M_\odot$ and $100\,M_\odot$ (see equation \ref{['imf']}).
• Figure 2: Evolution of the $B\!-\!V$ and $V\!-\!K$ colours and stellar mass-to-light ratio $M/L_V$ of simple stellar populations of solar metallicity computed using the Geneva (dotted line), Padova 1994 (standard model; solid line) and Padova 2000 (dashed line) stellar evolution prescriptions and the STELIB/BaSeL 3.1 spectral calibration. All models have the 2003PASPchab IMF truncated at $0.1\,M_\odot$ and $100\,M_\odot$ (see equation \ref{['imf']}).
• Figure 3: Evolution of the $B\!-\!V$ and $V\!-\!K$ colours and stellar mass-to-light ratio $M/L_V$ of simple stellar populations of solar metallicity computed using the Padova 1994 stellar evolution prescription and the BaSeL 3.1 (dotted line), STELIB/BaSeL 1.0 (short-dashed line), STELIB/BaSeL 3.1 (standard model; solid line) and Pickles (long-dashed line) spectral calibrations. All models have the 2003PASPchab IMF truncated at $0.1\,M_\odot$ and $100\,M_\odot$ (see equation \ref{['imf']}).
• Figure 4: Evolution of the $B\!-\!V$ and $V\!-\!K$ colours and stellar mass-to-light ratio $M/L_V$ of simple stellar populations of solar metallicity computed using the Padova 1994 stellar evolution prescription and the STELIB/BaSeL 3.1 spectral calibration, for different IMFs: 2003PASPchab, 2001MNRAS.322..231K, 1955ApJ...121..161S and 1998simf.conf..201S. All IMFs are truncated at $0.1\,M_\odot$ and $100\,M_\odot$.
• Figure 5: Evolution of the $B\!-\!V$ and $V\!-\!K$ colours and stellar mass-to-light ratio $M/L_V$ of simple stellar populations of solar metallicity computed using our model (with the Padova 1994 stellar evolution prescription and the STELIB/BaSeL 2.2 spectral calibration; solid line), the 1997AA...326..950F P ÉGASE version 2.0 model (dotted line) and the 2002AA...391..195G model (dashed line). All models have the 2001MNRAS.322..231Kpresent-day IMF truncated at $0.01\,M_\odot$ and $100\,M_\odot$.