Haloes gone MAD: The Halo-Finder Comparison Project (1104.0949v1)

Abstract: [abridged] We present a detailed comparison of fundamental dark matter halo properties retrieved by a substantial number of different halo finders. These codes span a wide range of techniques including friends-of-friends (FOF), spherical-overdensity (SO) and phase-space based algorithms. We further introduce a robust (and publicly available) suite of test scenarios that allows halo finder developers to compare the performance of their codes against those presented here. This set includes mock haloes containing various levels and distributions of substructure at a range of resolutions as well as a cosmological simulation of the large-scale structure of the universe. All the halo finding codes tested could successfully recover the spatial location of our mock haloes. They further returned lists of particles (potentially) belonging to the object that led to coinciding values for the maximum of the circular velocity profile and the radius where it is reached. All the finders based in configuration space struggled to recover substructure that was located close to the centre of the host halo and the radial dependence of the mass recovered varies from finder to finder. Those finders based in phase space could resolve central substructure although they found difficulties in accurately recovering its properties. Via a resolution study we found that most of the finders could not reliably recover substructure containing fewer than 30-40 particles. However, also here the phase space finders excelled by resolving substructure down to 10-20 particles. By comparing the halo finders using a high resolution cosmological volume we found that they agree remarkably well on fundamental properties of astrophysical significance (e.g. mass, position, velocity, and peak of the rotation curve).

• The paper presents a systematic evaluation of halo-finding algorithms using controlled tests on both mock and cosmological datasets.
• It demonstrates that phase-space methods excel in recovering subhalo details, effectively detecting structures with as few as 10-20 particles.
• The study shows that the peak of the rotation curve is a stable mass proxy, highlighting the need for refined unbinding procedures in dense environments.

Overview of the Halo-Finder Comparison Project

The paper by Alexander Knebe et al. presents a comprehensive evaluation of dark matter halo finders, focusing on the reproducibility of halo properties in cosmological simulations. This comparison is broken down across various halo-finding methodologies, including friends-of-friends (FOF), spherical-overdensity (SO), and phase-space algorithms, within the context of both mock and cosmological datasets.

Main Objectives

The primary aim of this paper is to assess the consistency and accuracy of different halo finders. The authors introduce a series of structured test scenarios comprising artificially constructed haloes with known properties. This approach allows for a clear evaluation of how different algorithms perform under controlled conditions, measuring properties such as the number of particles, halo centers, bulk velocities, and the peak of rotation curves.

Key Findings

1. Mock Haloes:
   • All halo finders successfully identified mock haloes, with variability noted in the recovery of subhaloes, especially those placed closer to the center of denser host haloes.
   • Phase-space-based halo finders demonstrated superior sensitivity in resolving central substructure, performing well with as few as 10-20 particles.
   • Variations in the identification of subhalo properties were linked to the halo center definition and unbinding procedures.
2. Cosmological Simulation:
   • A substantial agreement between the mass functions derived from different halo finders was observed, though some divergences exist due to distinct methodologies employed by each finder.
   • The two-point correlation function of the halo population showcased consistent recovery of halo positions across different halo finders, reinforcing the reliability of the positional data.
3. Resolution and Radial Dependence Tests:
   • While most methods identified subhaloes down to 30-40 particles, phase-space methods excelled further at detecting smaller subhaloes.
   • The proximity of a subhalo to the host’s center had impacts on the particles recovered, yet the peak of the rotation curve proved to be a stable property less affected by tidal forces.

Implications

This extensive paper provides an important benchmark for halo identification techniques, crucial for comparing results from cosmological simulations. The insights gathered are particularly notable regarding the dependence of halo properties on algorithmic details and environmental context, such as the presence of larger host haloes.

The findings highlight the utility of using the peak of the rotation curve as a mass proxy over other common metrics, such as the number of enclosed particles. The results also underscore the necessity of sophisticated unbinding procedures, especially for subhaloes deeply embedding in larger structures.

Future Directions

This paper sets the stage for further refinement of halo-finding algorithms, emphasizing the need for improved methodologies in detecting subhaloes and ensuring the accurate assignment of particles. Future developments could focus on integrating more complex baryonic processes and exploring the intersection of cosmological simulation data with observational metrics.

Overall, the Halo-Finder Comparison Project makes a significant contribution to the field of cosmological simulations, providing a framework for the systematic analysis and improvement of halo finder algorithms.