Year: 2026
Type: preprint
Abstract: Cosmic filaments connect the nodes of the large-scale web and are thought to harbour a substantial fraction of the low-z baryon budget, yet a physically motivated framework for organising their diverse gas properties has been lacking. Here we show that the linear mass density $Λ$ = M_gas/L_fil, measured within the entropy radius r_K (the peak of the radial gas entropy profile) plays this role, analogous to mass in halo physics. Using TNG300-1 at z=0, we characterise the structural, thermodynamic, and chemical properties of 5637 filaments spanning more than two decades in $Λ$. Filaments form a continuous thermodynamic sequence with $Λ$, ranging from long, thin, cool, metal-poor structures to shorter, wider, hotter, and more enriched ones, with core temperatures spanning two orders of magnitude across the full WHIM window. The ratio of mass- to volume-weighted temperature reveals a shift in heat distribution: low-$Λ$ filaments have their hotter gas preferentially associated with denser material, whereas in high-$Λ$ filaments the hotter gas is diffuse. Well-defined scaling relations connect $Λ$ to temperature, electron density, pressure, entropy, and metallicity, with the T-$Λ$ scaling qualitatively consistent with gravitational heating. We present the first measurement of the gaseous linear mass density function, revealing a broad distribution with a flat low-$Λ$ regime and a steep exponential decline at high $Λ$, analogous to the halo mass function. The integrated Compton-y parameter $Y^{\rm int}$ scales systematically with $Λ$, providing a tSZ proxy accessible to current surveys. Finally, galaxy richness per unit length correlates tightly with $Λ$ (Pearson r=0.80), enabling $Λ$-based classification of filaments from spectroscopic surveys alone and guiding targeted searches for the missing baryons in the cosmic web.
Source: arXiv (Cornell University)
Institutions: Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo, Yale University, Centre National de la Recherche Scientifique, Université Paris Sciences et Lettres, Observatoire de Paris, Sorbonne Université, Université Paris-Saclay, Institut d'Astrophysique Spatiale
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7223070337