SCYON Abstract

Received on May 8 2006

The radii of thousands of star clusters in M51 with HST/ACS

AuthorsR.A. Scheepmaker (1)
M. Gieles (1)
M.R. Haas (2)
N. Bastian (2)
S.S. Larsen (1)
H.J.G.L.M. Lamers (1,3)
(1) Astronomical Institute, Utrecht University, Princetonplein 5, NL-3584 CC Utrecht, The Netherlands
(2) Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, United Kingdom
(3) SRON Laboratory for Space Research, Sorbonnelaan 2, NL-3584 CA Utrecht, The Netherlands
To appear inThe proceedings of the conference, "Globular Clusters: Guides to Galaxies", held in Concepcion, 06/03 - 10/03/2006, ESO/Springer, eds. T. Richtler & S. S. Larsen


We exploit the superb resolution of the new HST/ACS mosaic image of M51 to select a large sample of young (<1 Gyr) star clusters in the spiral disk, based on their sizes. The image covers the entire spiral disk in B, V, I and Hα, at a resolution of 2 pc per pixel. The surface density distribution of 4357 resolved clusters shows that the clusters are more correlated with clouds than with stars, and we find a hint of enhanced cluster formation at the corotation radius. The radius distribution of a sample of 769 clusters with more accurate radii suggests that young star clusters have a preferred effective radius of ~3 pc, which is similar to the preferred radius of the much older GCs. However, in contrast to the GCs, the young clusters in M51 do not show a relation between radius and galactocentric distance. This means that the clusters did not form in tidal equilibrium with their host galaxy, nor that their radius is related to the ambient pressure.