Clusters in the solar neighbourhood: How are they destroyed?

Abstract

We predict the survival time of initially bound star clusters in the solar neighbourhood taking into account: (1) stellar evolution, (2) tidal stripping, (3) shocking by spiral arms and (4) encounters with giant molecular clouds. We find that the predicted dissolution time is tdis = 1.7(M i/104 M⊙)0.67 Gyr for clusters in the mass range of 102 < Mi < 105 M⊙. The resulting predicted shape of the logarithmic age distribution agrees very well with the empirical one, derived from a complete sample of clusters in the solar neighbourhood within 600 pc. The required scaling factor implies a star formation rate of 4 × 102 M ⊙ Myr-1 within 600 pc from the Sun or a surface formation rate of 3.5 × 10-10 M⊙ yr -1 pc-2 for stars in bound clusters with an initial mass in the range of 102 to 3 × 104 M⊙. © ESO 2006.