A Hubble Space Telescope/WFPC2 Survey of Bright Young Clusters in M31. III. Structural Parameters
Surface brightness profiles for 23 M31 star clusters were measured using images from the Wide Field Planetary Camera 2 on the Hubble Space Telescope, and fitted to two types of models to determine the clusters' structural properties. The clusters are primarily young (~10^8 yr) and massive (~10^(4.5) M_⊙), with median half-light radius 7 pc and dissolution times of a few Gyr. The properties of the M31 clusters are comparable to those of clusters of similar age in the Magellanic Clouds. Simulated star clusters are used to derive a conversion from statistical measures of cluster size to half-light radius so that the extragalactic clusters can be compared to young massive clusters in the Milky Way. All three sets of star clusters fall approximately on the same age-size relation. The young M31 clusters are expected to dissolve within a few Gyr and will not survive to become old, globular clusters. However, they do appear to follow the same fundamental plane (FP) relations as old clusters; if confirmed with velocity dispersion measurements, this would be a strong indication that the star cluster FP reflects universal cluster formation conditions.
Additional Information© 2009 The American Astronomical Society. Received 2009 July 31; accepted 2009 September 15; published 2009 October 30. We thank D.E. McLaughlin for the use of the GRIDFIT software. P.B. acknowledges research support through a Discovery Grant from the Natural Sciences and Engineering Research Council of Canada and an Ontario Early Researcher Award. S.P. and M.B. acknowledge the financial support of INAF through PRIN 2007 grant No. CRA 1.06.10.04: "The local route to galaxy formation." J.G.C. acknowledges support from NASA from grant GO-10818. T.H.P acknowledges support through the Plaskett Research Fellowship at the Herzberg Institute of Astrophysics.
Published - Barmby2009p6479Astron_J.pdf
Accepted Version - 0909.4053.pdf