On the origin of the clumpy streams of Palomar 5

In this paper we report a study (see Mastrobuono-Battisti et al., 2012) about the formation and characteristics of the tidal tails around Palomar 5 along its orbit in the Milky Way potential, by means of direct N-body simulations and simplified numerical models. Unlike previous findings, we are able to reproduce the substructures observed in the stellar streams of this cluster, without including any lumpiness in the dark matter halo. We show that overdensities similar to those observed in Palomar 5 can be reproduced by the epicyclic motion of stars along its tails, i.e. a simple local accumulation of orbits of stars that escaped from the cluster with very similar positions and velocities. This process is able to form stellar clumps at distances of several kiloparsecs from the cluster, so it is not a phenomenon confined to the inner part of Palomar 5's tails, as previously suggested.
Comment: 4 pages, 3 figures. To appear in the proceedings of the conference 'Reading the book of globular clusters with the lens of stellar evolution', Rome, Nov. 26-28, 2012, to be published in Memorie della Societa Astronomica Italiana, Eds. Paolo Ventura and Corinne Charbonnel