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Abstract:
We analyse the IllustrisTNG simulations to study the mass, volume fraction, and phase distribution of gaseous baryons embedded in the knots, filaments, sheets, and voids of the Cosmic Web from redshift z = 8 to redshift z = 0. We find that filaments host more star-forming gas than knots, and that filaments also have a higher relative mass fraction of gas in this phase than knots. We also show that the cool, diffuse intergalactic medium [IGM; T<10 5 K, n H <10 −4 (1+z)cm −3 ] and the warm-hot intergalactic medium [WHIM; 10 5 <T<10 7 K, n H <10 -4 (1+z)cm -3 ] constitute ∼39 and ∼46 per cent of the baryons at redshift z = 0, respectively. Our results indicate that the WHIM may constitute the largest reservoir of missing baryons at redshift z = 0. Using our Cosmic Web classification, we predict the WHIM to be the dominant baryon mass contribution in filaments and knots at redshift z = 0, but not in sheets and voids where the cool, diffuse IGM dominates. We also characterize the evolution of WHIM and IGM from redshift z = 4 to redshift z = 0, and find that the mass fraction of WHIM in filaments and knots evolves only by a factor of ∼2 from redshift z = 0 to 1, but declines faster at higher redshift. The WHIM only occupies 4−11 per cent of the volume at redshift 0 ≤ z ≤ 1. We predict the existence of a significant number of currently undetected O vii and Ne ix absorption systems in cosmic filaments, which could be detected by future X-ray telescopes like Athena.
