The splashback radius of halos from particle dynamics. I. The SPARTA algorithm

Understand

Motivated by the recent proposal of the splashback radius as a physical boundary of dark matter halos, we present a parallel computer code for Subhalo and PARticle Trajectory Analysis (SPARTA).

• The code analyzes the orbits of all simulation particles in all host halos, billions of orbits in the case of typical cosmological N-body simulations.
• Within this general framework, we develop an algorithm that accurately extracts the location of the first apocenter of particles after infall into a halo, or splashback.
• We define the splashback radius of a halo as the smoothed average of the apocenter radii of individual particles.