Siblings, friends and acquaintances: Testing galaxy association methods

TL;DR

This paper evaluates the limitations of galaxy association methods, specifically the Friends of Friends percolation technique, using cosmological simulation data to identify contamination issues and potential mitigation strategies.

Contribution

It provides an analysis of the Friends of Friends method's limitations in galaxy surveys and suggests thresholds and tests to reduce false positives.

Findings

High contamination for massive halos in dense environments

Thresholds can reduce fake associations

Substructure tests are effective in certain cases

Abstract

In order to constraint the limitations of association methods applied to galaxy surveys, we analysed the catalogue of halos at $z=0$ of a cosmological simulation, trying to reproduce the limitations that an observational survey deal with. We focused in the percolation method, usually called Friends of Friends method, commonly used in literature. The analysis was carried on the dark matter cosmological simulation MDPL2, from the Multidark project. Results point to a large fraction of contaminants for massive halos in high density environments. Thresholds in the association parameters and the subsequent analysis of observational properties can mitigate the occurrence of fake positives. The use of tests for substructures can also be efficient in particular cases.