  The galaxy distribution in dark matter-dominated halos is expected to
approximately trace the details of the underlying dark matter substructure. In
this paper we introduce halo `core-tracking' as a way to efficiently follow the
small-scale substructure in cosmological simulations and apply the technique to
model the galaxy distribution in observed clusters. The method relies on
explicitly tracking the set of particles identified as belonging to a halo's
central density core, once a halo has attained a certain threshold mass. The
halo cores are then followed throughout the entire evolution of the simulation.
The aim of core-tracking is to simplify substructure analysis tasks by avoiding
the use of subhalos and, at the same time, to more easily account for the
so-called ``orphan'' galaxies, which have lost substantial dark mass due to
tidal stripping. We show that simple models based on halo cores can reproduce
the number and spatial distribution of galaxies found in optically-selected
clusters in the Sloan Digital Sky Survey. We also discuss future applications
of the core-tracking methodology in studying the galaxy-halo connection.
