Color and spectral synthesis of disk galaxies

Models of the integrated colors and spectra of disk galaxies are constructed and used to investigate the effect of the star formation history and the initial mass function on the observational properties of galaxies. The models are constructed using evolutionary synthesis techniques. The selection of the components comprising the stellar populations and the parameters of galactic evolution are presented and described. The difficulties and problems of synthesizing composite stellar systems that include very young populations are discussed. Variations of the synthetic broad-band colors and line strengths are used to study different star-formation scenarios and different forms of the initial mass function. Three different star-formation histories are studied: an exponentially decreasing star-formation rate, star formation that is cut off or truncated, and bursts of star formation superimposed on an old, existing population. Three forms of the initial mass function are used in the models: a power law, a function with a single peak, and a bimodal function. The models are compared to observed nearby galaxies and to galaxies in the distant cluster Cl 1446+2619