Sursauts radio rapides : le spectre de puissance angulaire comme sonde cosmologique ✛

Résumé original

tel que rédigé par les auteurs, en anglais arXiv:2607.04106v1

Fluctuations in the cosmic electron density are imprinted on the dispersion measures (DMs) of fast radio bursts (FRBs), making DMs a promising probe of cosmology and the spatial distribution of ionized baryons. In this work, we present the first measurement of the angular auto-power spectrum of FRB DMs, using 3455 apparently non-repeating bursts from the CHIME/FRB Catalog 2. We detect an angular correlation signal at $$>3\sigma$$ significance, associated with large-scale electron-density fluctuations. By fitting the measured spectrum to theoretical models, we constrain two key parameter combinations: $$\Omega_{\rm b}h^2$$-$$H_0$$, which probes the cosmic baryon density and expansion rate, and $$\Omega_{\rm b}h^2$$-$$f_{\rm d}$$, which traces the baryon fraction in cosmic large-scale structure (LSS). We further assess the robustness of the power-spectrum method against systematic uncertainties arising from the assumed FRB redshift distribution and from the DM contributions of host galaxies ($${\rm DM}_{\rm host}$$), the Galactic halo ($${\rm DM}^{\rm MW}_{\rm halo}$$), and the Milky Way interstellar medium ($${\rm DM}^{\rm MW}_{\rm ISM}$$), using mock samples. Our results demonstrate that the angular power spectrum is largely insensitive to uncorrelated DM components such as $${\rm DM}_{\rm host}$$, thereby effectively mitigating the impact of poorly constrained host-galaxy systematics. In contrast to the traditional $${\rm DM}_{\rm LSS}$$-$$z$$ relation, this method does not require individual redshift measurements--it relies only on the overall redshift distribution--and it partially breaks the parameter degeneracies in the $$\Omega_{\rm b}h^2$$-$$H_0$$ and $$\Omega_{\rm b}h^2$$-$$f_{\rm d}$$ planes. These findings establish the DM angular power spectrum as a robust cosmological probe and a powerful baryon tracer.