Subhaloes gone Notts: Spin across subhaloes and finders

TL;DR

This study compares the spin distributions of subhaloes in two cosmological simulations using various finders, revealing how spin relates to subhalo location, mass, and the unbinding process.

Contribution

It systematically analyzes how different substructure finders and simulation parameters affect the measured spin distributions of subhaloes.

Findings

Spin distribution indicates the effectiveness of unbinding procedures.

Subhaloes closer to the host halo have lower spin.

Subhaloes are less rotationally supported than field haloes.

Abstract

We present a study of a comparison of spin distributions of subhaloes found associated with a host halo. The subhaloes are found within two cosmological simulation families of Milky Way-like galaxies, namely the Aquarius and GHALO simulations. These two simulations use different gravity codes and cosmologies. We employ ten different substructure finders, which span a wide range of methodologies from simple overdensity in configuration space to full 6-d phase space analysis of particles.We subject the results to a common post-processing pipeline to analyse the results in a consistent manner, recovering the dimensionless spin parameter. We find that spin distribution is an excellent indicator of how well the removal of background particles (unbinding) has been carried out. We also find that the spin distribution decreases for substructure the nearer they are to the host halo's, and that the value of the spin parameter rises with enclosed mass towards the edge of the substructure. Finally subhaloes are less rotationally supported than field haloes, with the peak of the spin distribution having a lower spin parameter.