2025/11/24 by Feng, Bocheng, Nadler, Ethan O., Oh, S. Peng +1
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics of Galaxies (astro-ph.GA) #Cosmology and Gravitation Theories #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena
paper · doi:10.48550/arxiv.2511.19250
openalex publication_date 2025/11/24 · openalex created_date 2025/11/27 · openalex updated_date 2026/07/28
Cosmological N-body simulations have long suggested that the pseudo phase-space density (PPSD), ρ/σ3, of cold dark matter haloes follows the universal relation ρ/σ3 ∝ rχ, with χ≈ -1.875, as predicted by spherical secondary-infall similarity solutions. This power law appears to hold despite the fact that neither the density ρ(r) nor velocity dispersion σ(r) follow universal power law relations individually, even at fixed mass. We analyze 246 host haloes from the Symphony suite of high-resolution cosmological zoom-in simulations, to consistently measure PPSD profiles across host masses from 1011 to 1015 M_\odot. We find that the PPSD systematically deviates from a power law, and that haloes with larger deviations from Jeans equilibrium systematically develop steeper average PPSD slopes. This result suggests that the PPSD is not universal; instead, it is linked to a halo's degree of dynamical equilibrium, which is ultimately set by halo formation history. As a result, we show that secondary halo properties such as concentration and accretion rate inherit significant correlations with the PPSD slope. Moreover, our hosts' PPSD profiles are remarkably consistent with predictions from one-dimensional self-similar fluid collapse models, indicating that three-dimensional structure, velocity anisotropy, and filamentary accretion all play negligible roles in shaping the PPSD. Thus, we argue that the PPSD is shaped by mass assembly alone, and that its non-universality reflects the diversity of halo growth histories.