The Filament Rift: ΛCDM’s Structural Challenge against Observation

Abstract This study presents the first extended comparison of cosmic filaments identified in Sloan Digital Sky Survey (SDSS) DR10 observations ( z < 0.05) and the IllustrisTNG300-1 ΛCDM simulation ( z = 0), utilizing the novel GrAviPaSt filament-finder method. The analyses are performed on both macro and microfilaments, each characterized by their length, thickness, and contrast in mass density. In addition to total sample comparisons, two subcategories of microfilaments, linking pairs of galaxy groups (GG) and linking pairs of galaxy clusters (CC), are introduced to further analyze discrepancies between the ΛCDM model and observation. While ΛCDM produces extended macrofilaments, such structures are largely absent from SDSS, and where present, they exhibit higher densities than their simulated counterparts. Microfilaments also show notable density discrepancies: at fixed length and thickness, observational filaments are significantly denser than those in the simulation. Employing radial density profiles reveal that microfilaments in the ΛCDM simulation exhibit higher contrasts in mass density relative to the background compared to their observational counterparts. Notably, CC-type microfilaments displayed enhanced density contrasts over GG types in the simulation, while observational data showed the opposite trend. Furthermore, SDSS galaxies in both GG and CC microfilaments exhibit lower specific star formation rates and older stellar populations, while TNG300-1 microfilaments host more actively star-forming galaxies within the intermediate stellar mass range. These results reveal persistent discrepancies between observational data and the ΛCDM reconstruction of cosmic filaments, pointing to possible tensions in our current understanding of large-scale structures and their environmental effects on galaxy evolution.