[Previous] | [Session 47] | [Next]
R. de Grijs, R.W. O'Connell (Astronomy Department, University of Virginia), J.S. Gallagher, III (Astronomy Department, University of Wisconsin)
We present high-resolution optical and near-infrared HST observations of two adjacent regions in the fossil starburst region in M82, M82 B. These observations allow us to study the evolved young cluster population associated with the fossil starburst. The presence of both the active and the fossil starburst in M82 provides a unique physical environment to study the stellar and dynamical evolution of such star cluster systems.
Age estimates based on theoretical modeling date the cluster population in the fossil starburst between ~2 \times 108 and ~109 years, assuming solar metallicity, with a peak in the distribution near the upper age limit. This implies that M/LV ~1.0, which leads to cluster mass estimates of ~104 - 105 M\odot, peaking near ~104 M\odot; extinction effects can shift the peak of the mass distribution to ~3 \times 104 M\odot.
The majority of the more extended sources in M82 B are characterized by 2.34 \le R\rm eff \le 8.4 pc, or 0.5 \le R\rm core \le 1.6 pc (with \langle R\rm core \rangle \approx 1.2 pc), with a wing extending to larger sizes, consistent with the Galactic globular cluster size distribution. It thus appears that the population of star cluster candidates in M82 B resembles the Galactic globular cluster population at a younger age. The radial luminosity profiles of the brightest clusters are more closely approximated by power laws than by a Gaussian model, in particular in their wings, which favors a slow star formation scenario.
RdeG was supported by NASA grants NAG 5-3428 and NAG 5-6403.