Cosmo-26

Deconstructing the missing baryon environment with Fast Radio Bursts

Not scheduled

20m

Gorlaeus gebouw (Leiden University)

Talk Large-Scale Structure

Speaker

Koustav Konar (University of Groningen and Stellenbosch University)

Description

The precise distribution of baryons in the Universe remains an open question in cosmology, as their highly diffuse nature renders direct observation difficult, while being integral in achieving precise cosmological inference in studies of gravitational lensing, galaxy evolution and the cosmic microwave background radiation with the current and upcoming surveys. We use Fast Radio Bursts (FRBs) and their dispersion measures (DMs) to probe and localise this baryon distribution in the large-scale structure (LSS) of the Universe.

Using the IllustrisTNG simulations, we classify the LSS into eight density bins of increasing matter density, analogous to voids, filaments, and haloes. We model the DM contribution from these density environments and compare them to observed DMs to infer the density estimator, defined as the ratio of the electron number density and the total matter density. The solution of such an overdetermined system is carried out within a Bayesian framework with a physics-informed prior model. To demonstrate observational applicability, we create a \textit{Eulcid}-like mock galaxy catalogue and build a density estimator based on luminous matter along the line of sight of an FRB. We apply a bias correction to account for the underlying dark matter distribution and compare the two density estimators to recover the electron number density across the eight density bins.

We show that electrons are mostly localised in low-density regions while accounting for the global theoretical estimate. Combining the density estimators from FRB and galaxies, we recover the baryon density as $\Omega_\mathrm{b} = 0.0472 \pm 0.0032$ (against $0.0486 \pm 0.0005$ as the true value). Our result of bin-wise electron density successfully reproduces the simulation ground truth to within 10 per cent. It showcases the distribution of baryons in three regions of the LSS as $f_\mathrm{gas}^\mathrm{void} = 0.213 \pm 0.023, f_\mathrm{gas}^\mathrm{filament} = 0.182 \pm 0.032$ and $f_\mathrm{gas}^\mathrm{halo} = 0.078 \pm 0.014$ against the ground truth of 0.22, 0.196 and 0.062, respectively.

This framework provides a novel, quantitative approach to addressing the missing baryon problem and offers a new way to constrain baryonic feedback mechanisms in future surveys such as CHORD and Euclid.