Galaxies as Laboratories for Studying Stellar Evolution
Claus Leitherer

Modeling the spectral energy distributions of galaxies requires assumptions on input parameters ranging laboratory astrophysics (such as dust properties), star-formation processes (such as the stellar IMF), stellar model atmospheres, or the star-formation histories. In this talk I will concentrate on an often neglected aspect: stellar evolution. The two most important components of a typical galaxy population in terms of their luminosity contribution are AGB and OB stars. Yet their physics is still poorly understood. I will show new results related to these (and other stars) and how they affect the interpretation of galaxy SEDs. The processes I will address are stochastic biases and their effects on synthetic populations, short eruptive evolutionary phases, and stellar rotation. I will discuss how neglecting these processes can lead to serious biases in the derived galaxy properties, such as the IMF, the number of ionizing photons, or the M/L ratio.