Core Tracking with Massless-Aggregation-Particles (MAPs)
Alexander Johnson, Harvard University
We introduce the concept of massless-aggregation-particles (MAPs) to track the cores of dark matter halos in large N-body simulations. MAPs are massless particles which shadow the dark-matter in a simulation and are capable of inelastically colliding according to a prescribed set of phase-space criteria. By being massless, the particles simulate baryons tracking the distribution of dark matter and by inelastically colliding the particles simulate a faux "cooling" process through the loss of kinetic energy. The phase-space criteria are constructed so that groups of particles satisfying tcool < tH0 inelastically collide to form "cooled" cores. These cores represent galaxy formation sites and are subsequently capable of accreting more MAPs and/or merging with other cores, thereby simulating the process of structure formation. The resulting set of MAPs then corresponds a distribution of halo/galaxy sites which is more realistic than those determined from typical methods such as friends-of-friends (FOF) because it includes additional information such as the details of the formation history and "effective" radiative cooling. We show that these MAPs can be used to make more effective mock catalogs to compare with future observations of the LSS.