We thank A. Bosma and the referee, A. Romeo, for their helpful comments. We also wish to thank Lars Hernquist for kindly providing us with the vectorised version of the treecode, and the "Institut de développement et des resources en informatique scientifique, Orsay, France (I.D.R.I.S.)" for the allocation of computer time. Part of this work was supported by the Dirección General de Investigación y Tecnologa under contract PB 93-0824-C02-02.
© European Southern Observatory (ESO) 1997
Online publication: April 6, 1998