The Disruption Time of Clusters in Selected Regions of Four Galaxies

Abstract.

If the cluster formation rate is constant and the disruption time of clusters depends on their initial mass as $t_{\rm dis} = t_4 \times (M_{\rm cl}/10^4 M_\odot)^\gamma$, the values of t ₄ and $\gamma$ can be derived in a very simple way from the age and mass histograms of large homogeneous samples of clusters with reliable age and/or mass determinations. We demonstrate the method and derive the values of t ₄ and $\gamma$ from cluster samples in selected fields of four galaxies: M51, M33, SMC and the solar neighbourhood. The values of $\gamma$ are the same within their uncertainties in the four galaxies with $< \gamma > = 0.62 \pm 0.06$. However, the disruption time t ₄ of clusters of $10^4 M_\odot$ is very different in the different locations. It is shortest in the inner region of M51 ( t ₄ = 4 x 10⁷ yrs) and highest in the SMC ( t ₄ = 4 x 10⁹ yrs).