Intensity profiles and color distributions in the nonnuclear regions of Sb galaxies.

Intensity profiles, isophotes, and color distributions for a sample of four nearby Sb galaxies indicate: (1) The "exponential disk" in this type of object is uniform in color out to a radius of 15 kpc, where it appears to either change abruptly or merge into the halo. (2) The color indices and outer isophotes of the regions beyond this "merger point" are consistent with a metal-poor "halo" population enriched with BHB stars and possibly some M dwarfs. (3) Observed "red excesses" in the outer regions of one of these spiral galaxies may conceivably be explained by tidal interaction with nearby galaxies.