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Session 79 - Star Clusters in Other Galaxies.
Display session, Friday, January 09
We have identified 1057 globular cluster candidates in a WFPC2 image of the inner region of M87. The Globular Cluster Luminosity Function (GCLF) of these clusters can be well fit by a Gaussian profile with a mean value of m_v^0=23.67\pm0.07 mag and \sigma=1.39\pm0.06 mag. The GCLF in five radial bins is found to be statistically the same at all points, showing no clear evidence of dynamical destruction processes based on the luminosity function. There is also no obvious trend between the effective radius of the clusters and the galactocentric radius. However, the core radius of the globular cluster density distribution is calculated to be R_c=56.2'', considerably larger than the core of the stellar halo (R_c=6.8''). We believe that this may primarily be a relic of the formation and/or accretion history of the clusters since neither the luminosity function, nor the size distribution show clear evidence of destruction processes. The color distribution of the clusters was found to be bimodal in all five radial bins with a blue peak at V-I=0.95 mag, a red peak at V-I=1.20 mag, and a mean color of V-I=1.09 mag. The red population is only 0.1 magnitude bluer than the underlying galaxy, indicating that these clusters may have formed late in the metal enhancement history of the galaxy. This is consistent with the theory that they may have been created in a burst of star/cluster formation roughly 9 Gyr ago during a major merger event. We also find tentative evidence for the red clusters being more centrally concentrated (a prediction of the merger hypothesis) and 10% smaller than the blue clusters.
Program listing for Friday