The COpernicus COmplexio: Statistical Properties of Warm Dark Matter Haloes

TL;DR

This paper investigates the properties of warm dark matter haloes formed in high-resolution cosmological simulations, revealing differences in structure, abundance, and evolution compared to cold dark matter haloes, especially at dwarf galaxy scales.

Contribution

It provides detailed simulation-based analysis of 7 keV sterile neutrino dark matter haloes, highlighting their structural and evolutionary differences from cold dark matter haloes.

Findings

Fewer low-mass haloes in WDM compared to CDM.

WDM haloes have lower concentrations on dwarf galaxy scales.

Halo shapes are similar, but smallest WDM haloes rotate more slowly.

Abstract

The recent detection of a 3.5 keV X-ray line from the centres of galaxies and clusters by Bulbul et al. (2014a) and Boyarsky et al. (2014a) has been interpreted as emission from the decay of 7 keV sterile neutrinos which could make up the (warm) dark matter (WDM). As part of the COpernicus COmplexio (COCO) programme, we investigate the properties of dark matter haloes formed in a high-resolution cosmological $N$-body simulation from initial conditions similar to those expected in a universe in which the dark matter consists of 7 keV sterile neutrinos. This simulation and its cold dark matter (CDM) counterpart have $\sim13.4$bn particles, each of mass $\sim 10^5\, h^{-1} M_\odot$, providing detailed information about halo structure and evolution down to dwarf galaxy mass scales. Non-linear structure formation on small scales ($M_{200}\, \leq\, 2 \times 10^9\,h^{-1}\,M_\odot$) begins slightly later in COCO-Warm than in COCO-Cold. The halo mass function at the present day in the WDM model begins to drop below its CDM counterpart at a mass $\sim 2 \times 10^{9}\,h^{-1}\,M_\odot$ and declines very rapidly towards lower masses so that there are five times fewer haloes of mass $M_{200}= 10^{8}\,h^{-1}\,M_\odot$ in COCO-Warm than in COCO-Cold. Halo concentrations on dwarf galaxy scales are correspondingly smaller in COCO-Warm, and we provide a simple functional form that describes its evolution with redshift. The shapes of haloes are similar in the two cases, but the smallest haloes in COCO-Warm rotate slightly more slowly than their CDM counterparts.