Color Gradients in M99: Stellar Populations or Dust?
González & Graham (1996a, b) discovered an azimuthal age gradient in the stellar population across one of the arms of M99, in what amounts to the first observational confirmation of a fundamental prediction of spiral density wave theory. A more exhaustive comparison of the color gradient with stellar population synthesis models seems to rule out a wave as old as 1010 yr, in favor of a duration of a few times 108 yr. By using new models that include the effects of mixed-in dust, we confirm that dust plays a minor role in the determination of the azimuthal color changes in this region of M99. We advance some possible new explanations for the overwhelming non-detection of convincing stellar population gradients across spiral arms.
KeywordsStar Formation Stellar Population Young Star Initial Mass Function Color Gradient
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- Charlot, S., Worthey, G., & Bressan, A. 1996, ApJ, 457, in pressGoogle Scholar
- González, R. A., & Graham, J. R. 1996a, ApJ, April 1, in press, “Tracing the Dynamics of Disk Galaxies with Optical and Infrared Surface Photometry: Color Gradients in M99”Google Scholar
- González, R. A., & Graham, J. R. 1996b, in Proc. of Conf. on Spiral Galaxies in the Near IR, Garching, ed. D. Minniti, Springer Verlag, in press, “Azimuthal Color Gradients in M99”Google Scholar
- Van Dyk, S. 1995, private communication.Google Scholar