A gas-rich cosmic web revealed by the partitioning of the missing baryons
Creators
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Connor, Liam1, 2
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Ravi, Vikram2
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Sharma, Kritti2
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Ocker, Stella Koch2, 3
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Faber, Jakob2
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Hallinan, Gregg2
- Harnach, Charlie2
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Hellbourg, Greg2
- Hobbs, Rick2
- Hodge, David2
- Hodges, Mark2
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Kosogorov, Nikita2
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Lamb, James2
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Law, Casey2
- Rasmussen, Paul2
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Sherman, Myles2
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Somalwar, Jean2
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Weinreb, Sander2
- Woody, David2
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Konietzka, Ralf M.1
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1.
Harvard-Smithsonian Center for Astrophysics
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2.
California Institute of Technology
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3.
Carnegie Observatories
Abstract
Approximately half of the Universe’s dark matter resides in collapsed halos; significantly less than half of the baryonic matter (protons and neutrons) remains confined to halos. A small fraction of baryons are in stars and the interstellar medium within galaxies. The majority are diffuse (<10−3 cm−3) and ionized (neutral fraction <10−4), located in the intergalactic medium (IGM) and in the halos of galaxy clusters, groups and galaxies. This diffuse ionized gas is notoriously difficult to measure, but has wide implications for galaxy formation, astrophysical feedback and precision cosmology. Recently, the dispersion of extragalactic fast radio bursts (FRBs) has been used to measure the total content of cosmic baryons. Here we present a large cosmological sample of FRB sources localized to their host galaxies. We have robustly partitioned the missing baryons into the IGM, galaxy clusters and galaxies, providing a late-Universe measurement of the cosmic baryon abundance, x03A9bh70 = 0.051^(+0.006)_(-0.006) where Ωb is the baryon density parameter and h70 is the scaled Hubble constant. Our results indicate efficient feedback processes that can deplete galaxy halos and enrich the IGM (total baryon fraction in the IGM is f_(IGM) = 0.76^(+0.10_(-0.11)), agreeing with the baryon-rich cosmic web scenario seen in cosmological simulations. Our results may reduce the ‘S8 tension’ in cosmology, as strong feedback leads to suppression of the matter power spectrum.
Copyright and License
© The Author(s), under exclusive licence to Springer Nature Limited 2025.
Acknowledgement
We thank F. Walter, X. Prochaska and M. Oei for informative conversations. We also thank D. Nelson and C. Walker for their considerable help with IllustrisTNG.
Data Availability
The FRB data presented here are publicly available in a CSV file (Supplementary Data 1) and at the following link: https://github.com/liamconnor/frb_baryon_connor2024/blob/main/data/frbsample_connor0924.csv.
Code Availability
We have created a reproduction package for our work that includes all code used for our data analysis and the production of each figure. We have placed this code on GitHub at https://github.com/liamconnor/frb_baryon_connor2024.
Supplemental Material
Supplementary Figs. 1 and 2, Discussion on ‘comparison with simulations’, and Table 1 with extra information on the optical FRB host galaxies.
Properties of the FRBs used in this work.
Extended data:
Extended Data Fig. 1 Optical/IR images of nine DSA-110 discovered FRB fields
Extended Data Fig. 2 The DM and total baryon distributions in IllustrisTNG
Extended Data Fig. 4 A direct measurement of the diffuse gas content
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Additional details
Dates
- Accepted
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2025-04-28
- Available
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2025-06-16Published online