Letter to the Editor

How universal are the two young cluster sequences?^*

The cases of the LMC, SMC, M 83, and the Antennae

¹ Physikalisches Institut, University of Cologne, Zülpicher Str. 77, 50937 Cologne, Germany e-mail: pfalzner@ph1.uni-koeln.de
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Received: 9 July 2009
Accepted: 7 October 2009

Abstract

Aims. Recently a new analysis of cluster observations in the Milky Way found evidence that clustered star formation may work under tight constraints with respect to cluster size and density, implying that only two sequences exist. Our aim is to investigate whether similar sequences can be found in other nearby galaxies.

Methods. This is done using data of cluster properties from the literature.

Results. For the extragalactic young stellar clusters we detect an overall trend in the cluster-density scaling that is comparable to the relation obtained for Galactic clusters, although differences may exist. For the LMC and SMC clusters, the densities are below the Galactic data points and/or the core radii are smaller than those of data points with comparable density. For M 83 and the Antenna clusters, the core radii are possibly comparable to the Galactic clusters but it is unclear whether they have similar expansion speeds. These findings should serve as an incentive to performing more systematic observations and analysis to answer the question of why there may be a similarity between young Galactic and extragalactic star cluster sequences.