The star cluster population of M 51

III. Cluster disruption and formation history

¹ Astronomical Institute, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands e-mail: gieles@astro.uu.nl
² SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands

Received: 21 February 2005
Accepted: 27 May 2005

Abstract

In this work we concentrate on the evolution of the cluster population of the interacting galaxy M 51 (NGC 5194), more precisely the timescale of cluster disruption and possible variations in the cluster formation rate. We present a method to compare observed age vs. mass number density diagrams with predicted populations including various physical input parameters like the cluster initial mass function, cluster disruption, cluster formation rate and star bursts. If we assume that the cluster formation rate increases at the moments of the encounters with NGC 5195, we find an increase in the cluster formation rate of a factor of , combined with a disruption timescale which is slightly higher than when assuming a constant formation rate ( yr vs.  yr). The measured cluster disruption time is a factor of 5 shorter than expected on theoretical grounds. This implies that the disk of M 51 is not a preferred location for survival of young globular clusters, since even clusters with masses on the order of will be destroyed within a few Gyr.