Wednesday, May 13, 2009 - 3:15pm
Carlo Giocoli (ITA):
"Hierarchical Clustering: Subhalo Population in Dark Matter Haloes: gamma-ray detectability"
Abstract. Using a cosmological N-Body simulation I followed the hierarchical growth of dark matter haloes along the cosmic time. The progenitor haloes accreted by the main halo have been followed until the present time and their mass loss rate has been studied and modeled. I find that the average, specific mass-loss rate of dark matter subhaloes depends mainly on redshift, with only a very weak dependence on the instantaneous ratio between the mass of the subhalo, msb, and that of the host halo at that time Mv. In fact, to good approximation, subhalo masses `decay' exponentially, with a decay time that is proportional to the instantaneous dynamical time of the host halo. Combined with the fact that more massive haloes assemble later, these results suggest a pleasingly simple picture for the evolution and mass dependence of the evolved subhalo mass function. This model can be applied to semi-analytical methods of galaxy formation, to accurately follow the time evolution of subhalo masses. As an application I will show how the subhalo population of dark matter haloes can be constructed using Monte-Carlo technique and the mass loss rate recipe measured in the simulation. Using a modified version the Sheth & Lemson 1999 algorithm for a lambda cold dark matter power spectrum, I model the growth of a Milky Way sized halo with microsolar mass resolution, corresponding to the typical Jeans mass for a dark matter Weakly Interacting Massive Particle with mass of 100 GeV. I then study the effect on the Fermi Large Area Telescope (GLAST) detectability for both subhaloes in the Milky Way and in Draco, and I show how subhaloes cannot be responsible for the boost factor needed for detection.