Multimass spherical structure models for N-body simulations

TL;DR

This paper introduces a multimass spherical modeling method for N-body simulations, significantly reducing computational time and enabling higher resolution studies of dark matter halo mergers and their core/cusp density evolution.

Contribution

The paper presents a new multimass technique for spherical models that enhances resolution and efficiency in N-body simulations, allowing detailed analysis of merger processes.

Findings

Models with up to 1.68 billion particles are stable over cosmological timescales.

In mergers, the steepest progenitor's cusp is preserved, confirming Dehnen's prediction.

Central density increases differ between core-core and cusp-cusp mergers, with cores being more protected.

Abstract

We present a simple and efficient method to set up spherical structure models for N-body simulations with a multimass technique. This technique reduces by a substantial factor the computer run time needed in order to resolve a given scale as compared to single-mass models. It therefore allows to resolve smaller scales in N-body simulations for a given computer run time. Here, we present several models with an effective resolution of up to 1.68 x 10^9 particles within their virial radius which are stable over cosmologically relevant time-scales. As an application, we confirm the theoretical prediction by Dehnen (2005) that in mergers of collisonless structures like dark matter haloes always the cusp of the steepest progenitor is preserved. We model each merger progenitor with an effective number of particles of approximately 10^8 particles. We also find that in a core-core merger the central density approximately doubles whereas in the cusp-cusp case the central density only increases by approximately 50%. This may suggest that the central region of flat structures are better protected and get less energy input through the merger process.