Analysing multi-wavelength data, collected/produced in ByoPiC, with novel statistical tools, we detected and characterised the ionised hot baryons in the comic web (CW) from the densest environments (galaxy clusters/groups) to the least dense ones (filaments).
The detection/characterisation of the ionised hot/warm gas content of the CW using the Planck SZ map and X-ray surveys was the heart of ByoPiC. Ever since the 90s, simulations showed that the missing baryons, constituting about half the ordinary matter, should be mainly in the filaments of the CW. ByoPiC hence focused on these environments to find evidence for the missing baryons. After the first significant detection of SZ signal in bridges between cluster-pairs, we focused on large (>30Mpc) filaments detected in the SDSS galaxy survey. We performed the very first detection of their stacked SZ signal, and hence their ionised gas content and we characterised the associated overdensity thanks to the analysis of the lensing maps from Planck. In the same filaments, we also measured for the very first time the X-ray emission from hot/warm ionised gas using ROSAT X-ray survey data, providing the first unambiguous evidence of missing hot/warm baryons in cosmic filaments. We confirmed this discovery using the early release data from the new generation X-ray survey eROSITA..
Based on publicly available hydrodynamic simulations, we have conducted detailed and comprehensive study of the matter distribution around filaments of the cosmic web. We showed for the first time the presence of two extreme populations of filaments: Short filaments short tracing dense environments, containing hot gas and connecting massive haloes and long filaments tracing lower-density environments, filled with warmer and connecting low-mass haloes. We derived the thermodynamic properties of the different gas phases in the short and long filaments and showed that the expected SZ signal in these cosmic web elements agrees with the one we measured in the actual SZ data from Planck.
We performed a systematic investigation of the interplay between filaments and galaxy clusters/groups (i.e. nodes of the CW). It necessitated the development of novel statistical estimators of the anisotropic matter distribution and of innovative filament detection methods. We have shown that the low density environment around clusters where they connect to the CW exhibits a significant anisotropic distribution of matter due to the filamentary pattern. With a harmonic decomposition, we studied the azimuthal distribution of galaxies and identified angular symmetries around clusters/groups, with our new filament detection method we estimated the connectivity to the CW. We found that cluster outskirts are dominated by a quadrupole configuration. We also found that highly connected clusters are more elliptical and grow faster than low-connectivity clusters. We also found that the warm/hot gas in filaments around clusters could explain the soft X-ray excess observed in the ROSAT data.
We unveiled the cosmological information in CW elements. The matter distribution in the universe is the result of the growth of initial density perturbations and their organisation in the cosmic web. The cosmological model governs this evolution and hence cosmological parameters can be inferred from the matter distribution. Using a suite of 44,000 publicly available numerical simulations spanning hundreds of cosmological models, we partitioned the cosmic web into all its elements (nodes, filaments, voids, walls) and performed the very first comprehensive analysis of their cosmological information content. We showed that determining the cosmological parameters from the combination of the CW environments improves the constraints by up to a factor ten.
