Color gradients in galactic spheroids. II - Gradient as a function of luminosity and morphology

Wirth, A. & Shaw, R. 1983. A. J. 88, 171.

Photoelectric surface photometry is presented for the stellar spheroids of galaxies covering a wide range in both luminosity and morphological type. Combining these data with those previously published has yielded a large, uniform sample of stellar spheroids with accurately measured color gradients. It is found that the bulges of spiral galaxies tend to have considerably larger color gradients perpendicular to their disks than pure spheroids of similar luminosity. These may be interpreted as metallicity gradients produced by the classical, gas dynamical disk galaxy formation picture. Pure spheroidal galaxies show small radial color gradients, perhaps indicative of a fairly homogeneous stellar population. There is some indication that the colors of the outer parts of low-luminosity ellipticals may be correlated with the compactness of the galaxy. The colors of a composite stellar system may be perturbed in either direction by the presence of a young population.