Cosmic Web Dissection in Fuzzy Dark Matter Cosmologies

Abstract

On large cosmological scales, anisotropic gravitational collapse is manifest in the dark cosmic web. Its statistical properties are little known for alternative dark matter models such as fuzzy dark matter (FDM). In this work, we assess for the first time the relative importance of cosmic nodes, filaments, walls and voids in a cosmology with primordial small-scale suppression of power. We post-process $N$-body simulations of FDM-like cosmologies with varying axion mass $m$ at redshifts $z\sim 1.0-5.6$ using the NEXUS+ Multiscale Morphology Filter technique at smoothing scale $Δx = 0.04 \ h^{-1}$Mpc. The formation of wall and void halos is more suppressed than naively expected from the half-mode mass $M_{1/2}$. Also, we quantify the mass and volume filling fraction of cosmic environments and find that 2D cosmic sheets host a larger share of the matter content of the Universe as $m$ is reduced, with an $\sim 8-12$\% increase for the $m=7 \times 10^{-22}$ eV model compared to CDM. We show that in FDM-like cosmologies, filaments, walls and voids are cleaner and more pronounced structures than in CDM, revealed by a strong mid-range peak in the conditioned overdensity PDFs $P(δ)$. At high redshift, low-density regions are more suppressed than high-density regions. Furthermore, skewness estimates $S_3$ of the total overdensity PDF in FDM-like cosmologies are consistently higher than in CDM, especially at high redshift $z\sim 5.6$ where the $m=10^{-22}$ eV model differs from CDM by $\sim 6 σ$. Accordingly, we advocate for the usage of $P(δ)$ as a testbed for constraining FDM and other alternative dark matter models.