A sample of 109 fast radio bursts with measured redshifts and dispersion measures is allowing scientists to map fluctuations in baryon density, revealing how energy injected during galaxy formation suppresses the clustering of matter within galaxy groups and clusters ranging from 10^(13)-10^(15) M_⊙. The work demonstrates that FRB data reduces the posterior variance at k~ 1 h Mpc-1 by a factor of approximately eight relative to the prior. Kritti Sharma of the California Institute of Technology and colleagues established fast radio bursts as a sensitive probe of feedback-regulated structure formation, and larger samples will further refine constraints on baryonic physics.
Fast Radio Bursts Probe Suppressed Matter Clustering
This improvement in precision stems from the unique ability of FRB dispersion measures to trace the integrated column density of free electrons along a sightline, offering an unbiased view of cosmic baryons. Unlike X-ray or Sunyaev-Zel’dovich effect measurements, FRB data is not significantly affected by cosmic infrared background contamination, allowing for a clearer signal of baryon distribution. Published FRBs with confident host associations, those with a host probability of 90 percent or greater, and spectroscopic redshifts were central to this analysis.
These bursts, represented as blue points on the derived p(DM_(exgal)|z_s) distribution, provide important data points for the halo model prescription used to infer gas profiles. “Together, these considerations underscore both the promise and the complexity of joint lensing-baryon analyses,” the authors write, highlighting the need for continued development of these complementary observational techniques to refine our understanding of cosmological parameters.
Baryon Distribution & Cosmological Information Encoding
Large-scale structure surveys, including those planned with the Vera Rubin Observatory and Euclid, aim to map cosmic matter distribution with percent-level precision via weak gravitational lensing. However, interpreting these measurements is complicated by the suppression of matter clustering caused by energy feedback during galaxy formation. Fast radio bursts now offer a complementary approach, providing a baryon distribution probe largely independent of the systematic errors affecting X-ray and thermal Sunyaev-Zel’dovich effect measurements.
Equations establishing the relationship between mean extragalactic dispersion measure and redshift, alongside the scatter in extragalactic dispersion measure at a given redshift, reveal valuable cosmological and astrophysical information. Bayesian inference, utilizing the assumption of independent FRB observations, defines the posterior probability for parameters governing feedback processes and host galaxy properties. This posterior is proportional to the product of likelihood functions, quantifying the agreement between observed dispersion measures and model predictions, multiplied by the prior distribution on free parameters.
The ability to constrain these parameters represents an advance in understanding how feedback regulates galaxy growth. This research demonstrates that FRB data can refine cosmological measurements by providing an independent assessment of baryon distribution.
FRB Dispersion Measures as a Baryon Probe
Fast radio bursts offer a unique advantage over existing methods for mapping cosmic baryons by remaining unbiased regarding density and temperature. This characteristic positions FRBs as a complementary tool to X-ray and Sunyaev-Zel’dovich effect measurements, both of which face limitations in fully quantifying feedback’s impact on the matter power spectrum. Current cosmic shear measurements demand precise knowledge of baryon distribution within halos of approximately 10^(13)-10^(15) M_⊙, a requirement that restricts reliable interpretation to scales of k~ 0.1-3 h Mpc⁻¹.
Sensitivity calculations reveal how FRB observations compare to conventional baryon probes, highlighting their potential to probe halo mass and redshift with distinct characteristics. The observed variance in FRB dispersion measures provides insight into the distribution of baryons, as illustrated by heatmap representations of best-fit distributions inferred from halo model prescriptions with flexible gas profiles.
Published FRBs, identified by confident host associations and spectroscopic redshifts, are shown as blue points on these maps, demonstrating the observational basis for this new probe. This work showcases the ability of FRBs to investigate the M_(200) > 10^(13) M_⊙ halo mass regime, an important area for understanding the suppression of matter power spectrum at scales of approximately 0.1-3 h Mpc⁻¹.
FRB Data Constrains Matter Power Spectrum at k~0.1-3 Mpc⁻¹
Measurements of matter distribution reveal the impact of energy release during galaxy formation, with new fast radio burst (FRB) data providing a particularly precise view at scales of k~ 0.1-3~h Mpc⁻¹. Analyses fixed cosmological parameters to the Planck18 TT,TE,EE+lowE+lensing model, alongside parameters defining baryon condensation and ejection (BCEmu) during galaxy evolution, to assess sensitivity of the measured matter power spectrum suppression.
Testing a shift to the DES-Y3 cosmology, with Ω_m = 0. 293 and σ_8 = 0. 764, showed changes in matter power spectrum suppression attributable to alterations in the universe’s baryon fraction, Ω_b/Ω_m. Exploring extreme scenarios, researchers found that a lack of feedback mechanisms favored minimal suppression of the matter power spectrum alongside higher gas mass fractions, demonstrating the current FRB sample possesses the ability to differentiate between these contrasting cases.
The constraining power of the data was quantified using the Kullback-Leibler (KL) divergence, measuring information gained relative to prior distributions; at a scale of k~ 1~h Mpc⁻¹, FRB data reduces the posterior variance by a factor of ~ 8 relative to the prior. This scale-dependent assessment of constraining power remains independent of arbitrary parameter normalization choices, offering a robust measure of data informativeness.
Parameters governing the halo gas profile, including log M_c, θ(ej), μβ, and δ, strongly influence both matter power spectrum suppression and gas fractions within R_(200). This finding confirms that both metrics serve as reliable indicators of gas physics at play within these structures.
Supplementary analysis evaluated the impact of stellar initial mass function on matter power spectrum suppression, utilizing observed stellar-to-halo mass relation data, further refining the understanding of these complex interactions. “Using the matter power spectrum suppression prior and posterior samples from observed FRBs, we find that the FRB data contribute an information gain of ~ 15 bits at scale k~ 1~h Mpc⁻¹,” the researchers report, highlighting the precision now achievable in mapping the distribution of matter across vast cosmic distances.
FRB Precision Matches Existing Baryon Tracers
Fast radio burst data is now achieving precision comparable to established methods for mapping cosmic structure, reducing the posterior variance at k~ 1 h Mpc⁻¹ by a factor of ~ 8 relative to the prior. This level of statistical power, derived from analysis of 109 fast radio bursts, positions FRBs as a complementary probe to existing baryon tracers despite utilizing a different redshift range.
The improved precision allows for more robust exclusion of extreme scenarios in galaxy formation simulations, specifically ruling out models like Illustris and OWLS-AGN at a confidence level of approximately 2σ. The influence of feedback processes on matter clustering is most pronounced within halos exceeding 10^(13)-10^(15) M_⊙, impacting the matter power spectrum at scales of roughly 0.1-3 h Mpc⁻¹.
Published FRBs, identified through confident host associations (with a host probability exceeding 0.9) and spectroscopic redshifts, are visually represented as blue points on heatmaps detailing inferred dispersion measure distributions. Current data suggests two robust and unbiased probes of feedback strength dominate the field: halo gas mass fractions within R₂₀₀ and matter power spectrum suppression at intermediate scales, both demonstrating relative insensitivity to uncertainties in stellar physics. “Together, these complementary tracers will, over the coming decade, bridge the longstanding divide between precision cosmology and the physics of galaxy formation,” the study notes.
Hydrodynamical Simulations & Feedback Model Uncertainties
Comparisons between inferred matter suppression and hydrodynamical simulations reveal notable discrepancies. The current work finds consistency, within one sigma, with simulations like BAHAMAS, SIMBA, and FLAMINGO, but diverges from results produced by Illustris, OWLS-AGN, and IllustrisTNG by 1. 4 to 2. 6 sigma. These variations highlight the challenges in accurately modeling active galactic nuclei (AGN) feedback and its complex interplay with other physical processes influencing the matter power spectrum.
Further analysis indicates a slight preference, 0. 6 to 0. 8 sigma, for higher gas mass density within R200 when compared to constraints derived from the kinematic and thermal Sunyaev-Zel’dovich effect. This suggests that feedback mechanisms, as probed by fast radio bursts, may be relatively weaker in the local Universe. However, researchers caution that a single parameter cannot fully capture the scale-dependent complexity of baryonic feedback, and the accuracy of models relies on the specific feedback implementation within simulations like BAHAMAS.
This model serves primarily as a cross-check against baseline results obtained with the BCEmu model, enabling controlled tests of systematic uncertainties related to dark matter contributions from host galaxies. The study utilizes parameters within the hydrodynamical simulations-calibrated halo model, including a log TAGN value fixed at 7. 8, representing the AGN heating temperature calibrated to BAHAMAS simulations.
Flexible analytical gas profiles are also modeled using the BCEmu framework, incorporating parameters like log Mc, a mass scale below which the gas profile deviates from the NFW profile, and μβ, representing the mass dependence of the inner gas profile slope. The posteriors for mock scenarios, including variants of BCEmu, demonstrate that extreme feedback scenarios predict strong suppression and low gas fractions, while scenarios with no feedback predict near-zero suppression and high gas fractions, aligning with expectations.
FRB Data Excludes Extreme Feedback Scenarios (Illustris, OWLS-AGN)
The observed data demonstrably reduces uncertainty in understanding how matter clusters across vast cosmic distances. These simulations, which model the complex interplay of energy and momentum in galaxy evolution, predict significantly different patterns of matter clustering than those indicated by the fast radio burst observations. Validation of the analysis pipeline involved the use of synthetic data, confirming its ability to differentiate between scenarios with varying degrees of feedback.
A comparison with literature values obtained from X-ray observations from surveys like eROSITA reveals consistency with theoretical predictions for FRBs originating in star-forming galaxies. As the researchers note, highlighting the ongoing need for multi-faceted approaches to understanding the universe’s structure.
Weak Lensing Surveys & Small-Scale Structure Challenges
Cosmological simulations model the hydrodynamic evolution of baryons alongside dark matter, providing a framework for studying galaxy formation’s impact on small-scale matter clustering. These simulations demonstrate that stellar and active galactic nucleus feedback redistribute gas within halos and can eject it beyond the virial radius, suppressing matter clustering on scales of roughly 0.1-1 Mpc. This suppression effectively limits the information available from small-scale structure, particularly at k~ 0.1-3 h Mpc-1, where baryonic feedback dominates.
Recent studies have attempted to address this limitation by combining weak lensing with complementary probes, including X-ray observations of galaxy clusters. Exploiting this potential requires ensuring unbiased cosmological inference, and this research provides a physically motivated approach to studying the impact of galaxy formation processes on small-scale matter clustering. Complex astrophysical processes regulate the growth of galaxies by injecting energy and momentum into their surroundings, redistributing baryons across megaparsec scales, and this new method offers a unique window into those processes.
Complementary Probes: X-ray & SZ Effects with FRBs
Joint analyses of weak gravitational lensing with other tracers offer a powerful method to disentangle astrophysical feedback effects from cosmological parameters, and fast radio bursts now provide a novel avenue for this approach. These limitations discard valuable small-scale information at scales of 1-10 h Mpc-1, where baryonic feedback exerts its strongest influence on matter distribution.
The research presented builds on these efforts, demonstrating how fast radio bursts can further refine our understanding of baryon distribution within halos, and thereby constrain feedback processes. Comparisons with literature values obtained from X-ray observations from surveys like eROSITA, as well as kSZ constraints from ACT DR5 stacks, demonstrate the consistency of FRB-derived measurements with existing baryon probes.
The ability of FRBs to probe baryon density fluctuations at specific scales complements existing techniques, offering a unique perspective on the interplay between dark matter and baryonic matter. This multi-messenger approach, combining FRBs with X-ray and Sunyaev-Zel’dovich effect measurements, promises to refine cosmological models and provide a more complete picture of galaxy formation and evolution.
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