Color Profiles of Spiral Galaxies: Clues on Outer Disk Formation Scenarios

We have explored radial color and stellar surface mass density profiles for a sample of 85 latetype spiral galaxies with deep (down to ∼27 mag/arcsec) SDSS g’ and r’ band surface brightness profiles. About 90% of the light profiles have been classified as broken exponentials, either exhibiting truncations (Type II galaxies) or antitruncations (Type III galaxies). The color profiles of Type II galaxies show a ’U-shape’ with a minimum of (g− r) = 0.47± 0.02 mag at the break radius. Around the break radius Type III galaxies have a plateau region with a color of (g − r) = 0.57± 0.02. Using the color to calculate the stellar surface mass density profiles reveals a surprising result. The breaks, well established in the light profiles of the truncated galaxies, are almost gone, and the mass profiles resemble now those of the pure exponential (Type I) galaxies. This result suggests that the origin of the break in Type II galaxies is more likely due to a radial change in stellar population than being associated to an actual drop in the distribution of mass. Type III galaxies however seem to preserve their shape in the stellar mass density profiles. We find that the stellar surface mass density at the break for truncated galaxies is 13.6± 1.6 M⊙pc and 9.9± 1.3 M⊙pc for the antitruncated ones. We estimate that the fraction of stellar mass outside the break radius is ∼ 15% for truncated galaxies and ∼ 9% for antitruncated galaxies. Subject headings: Galaxies: Evolution, Galaxies: Formation, Galaxies: Spiral, Galaxies: Structure Galaxies: Photometry