Cold versus Warm Dark Matter simulations of a galaxy group

TL;DR

This study compares cold and warm dark matter simulations of galaxy group formation, revealing that WDM fails to produce a Local Group-like structure and results in less concentrated baryons and different disk properties.

Contribution

It provides the first detailed comparison showing WDM's inability to form a realistic Local Group and highlights differences in baryon concentration and disk properties.

Findings

CDM forms a Local Group-like structure; WDM does not.

WDM results in a more diffuse, expanding galaxy group.

Baryon concentration and disk properties differ between CDM and WDM.

Abstract

The differences between cold (CDM) and warm (WDM) dark matter in the formation of a group of galaxies is examined by running two identical simulations where in the WDM case the initial power spectrum has been altered to mimic a 1keV dark matter particle. The CDM initial conditions were constrained to reproduce at z = 0 the correct local environment within which a "Local Group" (LG) of galaxies may form. Two significant differences between the two simulations are found. While in the CDM case a group of galaxies that resembles the real LG forms, the WDM run fails to reproduce a viable LG, instead forming a diffuse group which is still expanding at z = 0. This is surprising since, due to the suppression of small scale power in its power spectrum, WDM is naively expected to only affect the collapse of small haloes and not necessarily the dynamics on a scale of a group of galaxies. Furthermore the concentration of baryons in halo center's is greater in CDM than in WDM and the properties of the disks differ.