THE CATERPILLAR PROJECT: A LARGE SUITE OF MILKY WAY SIZED HALOS

ABSTRACT We present the largest number of Milky Way sized dark matter halos simulated at very high mass (∼104 /particle) and temporal resolution (5 Myr/snapshot) done to date, quadrupling what is currently available in the literature. This initial suite consists of the first 24 halos of the Caterpillar Project whose project goal of 60-70 halos will be made public when complete. We do not bias our halo selection by the size of the Lagrangian volume. We resolve ∼20,000 gravitationally bound subhalos within the virial radius of each host halo. Improvements were made upon current state-of-the-art halo finders to better identify substructure at such high resolutions, and on average we recover ∼4 subhalos in each host halo above 108 which would have otherwise not been found. The density profiles of relaxed host halos are reasonably fit by Einasto profiles ( = 0.169 0.023) with dependence on the assembly history of a given halo. Averaging over all halos, the substructure mass fraction is , and mass function slope is dN/d . We find concentration-dependent scatter in the normalizations at fixed halo mass. Our detailed contamination study of 264 low-resolution halos has resulted in unprecedentedly large high-resolution regions around our host halos for our fiducial resolution (sphere of radius Mpc). This suite will allow detailed studies of low mass dwarf galaxies out to large galactocentric radii and the very first stellar systems at high redshift (z 15).