  Using subspace methods, we study the distribution of physical components of
galaxies in wavelength space. We find that it is valid to assume that the
stellar and the gaseous components of galaxies span complementary subspaces. To
first order, stellar and gaseous spectral features can be extracted from galaxy
spectra through a simple matrix multiplication. By comparing the stellar
continua obtained respectively using the model-based and the empirical approach
through a commonality measure, we conclude that the latter may lose
higher-order spectral features.
