Differences in baryonic and dark matter scaling relations of galaxy clusters: A comparison between IllustrisTNG simulations and observations

We compare the self-similar baryonic mass fraction scaling relations between galaxy clusters from the South Pole Telescope Sunyaev–Zel’dovich (SPT-SZ) survey and the IllustrisTNG state-of-the-art magnetohydrodynamical cosmological simulations. Using samples of 218 (TNG100) and 1605 (TNG300) friends-of-friends (FoF) haloes within 0.0≤z≤1.5 and M200c≥7×1013 M⊙, we fit the scaling relations using Simple Power Law (SPL), Broken Power Law (BPL), and General Double Power Law (GDPL) models through non-linear least squares regression. The SPL model reveals null slopes for the baryonic fraction as a function of redshift, consistent with self-similarity. Observations and simulations agree within 1−2σ, suggesting comparable baryonic scaling slopes. We identify ∼13.8−14.1 per cent of baryons as “missing”, primarily in the form of intracluster light (ICL) across all halo masses and warm gas in low-mass haloes. High-mass haloes (log10(M500c/M⊙)≥14) adhere to self-similarity, while low-mass haloes exhibit deviations, with the breakpoint occurring at log10(M500c/M⊙)∼14, where baryons are redistributed to the outskirts. Our findings suggest that the undetected warm-hot intergalactic medium (WHIM) and baryon redistribution by feedback mechanisms are complementary solutions to the “missing baryon” problem.