Baryonic matter in cosmology
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Baryonic Matter and Its Role in Cosmology
Baryonic matter, which includes ordinary matter such as protons, neutrons, and electrons, plays a crucial role in shaping the universe’s structure and evolution. Understanding its effects is essential for interpreting cosmological observations and for distinguishing between the influences of baryons and dark matter.
Baryonic Feedback and Matter Distribution
Baryonic processes, such as star formation, supernovae, and active galactic nuclei (AGN) feedback, significantly impact the distribution of matter in the universe. These processes alter the amplitude and scale dependence of galaxy clustering and weak lensing observables, especially at separations under 10 Mpc. Accurate cosmological measurements require unbiased models that account for these baryonic effects on the matter power spectrum, $P(k,z)$, across different scales and redshifts 15.
Hydrodynamical simulations show that feedback from supernovae and AGN can cause baryons to spread much further from their initial positions compared to dark matter, with the extent of this spread being highly sensitive to the details of the feedback models used. This spread affects the clustering of matter and the suppression of power on small scales, which must be carefully modeled for precise cosmological studies 35.
Coupling Between Baryonic Feedback and Cosmology
Astrophysical feedback processes are not independent of cosmological parameters. The strength of baryonic feedback can be enhanced in cosmological models that suppress structure formation, such as those with massive neutrinos or decaying dark matter. The combined effect of baryonic and non-baryonic suppression mechanisms can be greater than the sum of their individual effects, influencing the matter power spectrum and potentially resolving tensions in cosmological measurements, such as the S8 tension .
Baryonic Features in the Matter Transfer Function
Baryons introduce distinct features in the matter transfer function, including acoustic oscillations and suppression of power below the sound horizon. These effects are prominent when the baryon fraction is high and must be accurately described to interpret large-scale structure observations. The main effect in standard cosmologies is a sharp suppression in the transfer function at small scales, which cannot be simply modeled by adjusting the shape parameter .
Baryons and Gravitational Lensing
Baryonic matter also affects gravitational lensing statistics. Simulations indicate that baryonic physics enhances the probability of strong lensing events, such as highly magnified objects and multiple images, by increasing the lensing strength of galaxy clusters. This effect is significant and must be considered when analyzing lensing data from large surveys 910.
Baryons in Galaxy Formation and Evolution
At the peak of galaxy formation, about ten billion years ago, observations suggest that many massive galaxies were strongly baryon-dominated in their inner regions, with dark matter playing a smaller role than in the present-day universe. This is inferred from rotation curves that decrease with radius, indicating efficient condensation of baryons at the centers of dark matter halos during periods of high gas fractions and less concentrated dark matter .
Baryon-Dark Matter Interactions
Interactions between baryons and dark matter, such as elastic scattering, can affect the dynamics of density perturbations in the early universe. Cosmological observations, including the cosmic microwave background and Lyman-alpha forest data, place strong constraints on the strength of these interactions. These constraints are important for understanding the thermal history of the universe and for ruling out certain dark matter models 68.
Conclusion
Baryonic matter is a key component in cosmology, influencing the distribution of matter, the formation and evolution of galaxies, and the interpretation of cosmological observables. Accurate modeling of baryonic effects is essential for extracting reliable information about the universe’s structure, the nature of dark matter, and the underlying cosmological parameters. As observational data improve, continued refinement of baryonic models will be critical for advancing our understanding of the cosmos.
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