Warmth Elevating the Depths: Shallower Voids with Warm Dark Matter

TL;DR

This study investigates how warm dark matter influences the structure of cosmic voids and the cosmic web, revealing that increased warmth results in shallower voids, fewer subvoids, and smoother filaments, which could help constrain dark matter properties.

Contribution

It demonstrates the impact of warm dark matter on void density profiles and substructure, providing new observational probes for dark matter characteristics.

Findings

Void density minima become shallower with increased WDM warmth.

Number of subvoids decreases as WDM particle mass decreases.

Filaments and walls become smoother with less substructure.

Abstract

Warm dark matter (WDM) has been proposed as an alternative to cold dark matter (CDM), to resolve issues such as the apparent lack of satellites around the Milky Way. Even if WDM is not the answer to observational issues, it is essential to constrain the nature of the dark matter. The effect of WDM on haloes has been extensively studied, but the small-scale initial smoothing in WDM also affects the present-day cosmic web and voids. It suppresses the cosmic "sub-web" inside voids, and the formation of both void haloes and subvoids. In $N$-body simulations run with different assumed WDM masses, we identify voids with the ZOBOV algorithm, and cosmic-web components with the ORIGAMI algorithm. As dark-matter warmth increases (i.e., particle mass decreases), void density minima grow shallower, while void edges change little. Also, the number of subvoids decreases. The density field in voids is particularly insensitive to baryonic physics, so if void density profiles and minima could be measured observationally, they would offer a valuable probe of the nature of dark matter. Furthermore, filaments and walls become cleaner, as the substructures in between have been smoothed out; this leads to a clear, mid-range peak in the density PDF.