Satellite survival in cold dark matter cosmology.pdfVIP

a r X i v : 0 7 0 5 .2 5 5 6 v 1 [ a s t r o - p h ] 1 7 M a y 2 0 0 7 Satellite Survival in CDM Cosmology C. M. Boily1 Observatoire astronomique, 11 rue de l’Universite?, F-67000 Strasbourg, France cmb@astro.u-strasbg.fr N. Nakasato2 Department of Astronomy, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan and R. Spurzem T. Tsuchiya3 Astronomisches Rechen-Institut, Mo?nchhofstrasse 12-14, D-69120 Heidelberg, Germany ABSTRACT We study the survival of sub-structures (clumps) within larger self-gravitating dark matter haloes. Building on scaling relations obtained from N -body calculations of violent relaxation, we argue that the tidal field of galaxies and haloes can only destroy sub-structures if spherical symmetry is imposed at formation. We explore other mechanisms that may tailor the number of halo sub-structures during the course of virialisation. Unless the larger halo is built up from a few large clumps, we find that clump-clump encounters are unlikely to homogenise the halo on a dynamical timescale. Phase-mixing would proceed faster in the inner parts and allow for the secular evolution of a stellar disc. 1. Introduction High-resolution simulations of structure forma- tion in an ΛCDM cosmogony have revealed a large number of substructures within dark mat- ter haloes (e.g. Ghigna et al. 2000; Moore 2001). The mass function of these dark clumps (Moore et al. 1999a; de Lucia et al. 2004) n(m) ∝ m?2 (1) in the mass range 108 to 1011 solar masses. These orbiting self-bound dark matter satellites would drag along baryonic matter to a non-negligible fraction of their mass. Consequently galaxies should harbour a large number of dwarf galaxies, 1Corresponding author 2Current address: Institute of Advanced Physical Chemical Research, 2-1 Hirosawa, Wako-shi, Saitama 351- 019, Japan 3Now at SGI Japan, Ltd., Ebisu Garden Place Tower 31F, 4-20-3 Ebisu, Shibuya-ku, Tokyo 150-6031, Japan when only a handful are found (Kauffmann et al. 1993; Moore et al. 1999a;