MACHOs in dark matter haloes

Abstract

Using eight dark matter haloes extracted from fully-self consistent cosmological N-body simulations, we perform microlensing experiments. A hypothetical observer is placed at a distance of 8.5 kpc from the centre of the halo measuring optical depths, event durations and event rates towards the direction of the Large Magellanic Cloud. We simulate 1600 microlensing experiments for each halo. Assuming that the whole halo consists of MACHOs, f = 1.0, and a single MACHO mass is m_M = 1.0 Msun, the simulations yield mean values of tau = 4.7^{+5.0}_{-2.2} 10^{-7} and Gamma = 1.6^{+1.3}_{-0.6} 10^{-6} events/star/year. We find that triaxiality and substructure can have major effects on the measured values so that tau and Gamma values of up to three times the mean can be found. If we fit our values of tau and Gamma to the MACHO collaboration observations (Alcock et al. 2000), we find f = 0.23^{+0.15}_{-0.13} and m_M = 0.44^{+0.24}_{-0.16}. Five out of the eight haloes under investigation produce f and m_M values mainly concentrated within these bounds.