Cosmic web dissection in fuzzy dark matter cosmologies

Abstract

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 (DM) 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 ∼ 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 M1/2. Also, we quantify the mass- and volume-filling fractions 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 ∼8−12 per cent increase for the m = 7 × 10−22 eV model compared to cold dark matter (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 S3 of the total overdensity PDF in FDM-like cosmologies are consistently higher than in CDM, especially at high redshift z ∼ 5.6 where the m = 10−22 eV model differs from CDM by ∼6σ. Accordingly, we advocate for the usage of P(δ) as a testbed for constraining FDM and other alternative DM models.