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

Bakos, Judit; Trujillo, I.; Pohlen, Michael
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The Astrophysical Journal, Volume 683, Issue 2, pp. L103-L106.

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We have explored radial color and stellar surface mass density profiles for a sample of 85 late-type spiral galaxies with deep (down to ~27 mag arcsec-2) SDSS g'- and r'-band surface brightness profiles. About 90% of the light profiles have been classified as broken exponentials, exhibiting either 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 now resemble 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 with 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 Msolar pc-2 and for the antitruncated ones is 9.9+/-1.3 Msolar pc-2. We estimate that the fraction of stellar mass outside the break radius is ~15% for truncated galaxies and ~9% for antitruncated galaxies.
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Traces of Galaxy Formation: Stellar populations, Dynamics and Morphology

We are a large, diverse, and very active research group aiming to provide a comprehensive picture for the formation of galaxies in the Universe. Rooted in detailed stellar population analysis, we are constantly exploring and developing new tools and ideas to understand how galaxies came to be what we now observe.

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