Probe the missing baryons in cosmic filaments with Fast Radio Bursts

Cosmic filaments are thought to host a substantial fraction of the missing baryons at redshifts $z<2$. In this study, we probe the baryonic content of these filaments using localized Fast Radio Bursts (FRBs). Filaments are identified from the galaxy distribution in the Dark Energy Spectroscopic Instrument (DESI) imaging surveys using the DisPerSe algorithm. We find tentative evidence ($\sim 3 σ$ significance) for a divergence in the relationship between the dispersion measure (DM) contributed by the intergalactic medium and redshift for FRBs whose signals intersect cosmic filaments compared to those that do not, suggesting excess baryons in the filamentary structures. Assuming an isothermal $β$-model gas profile with $β=2/3$, this discrepancy is best explained by a central baryon overdensity of $δ= 20.78$, broadly consistent with previous simulation and observational results. The inferred baryon fraction residing in filaments decreases with redshift, from approximately $0.25-0.30\,Ω_b$ at $z=0.02$ to $0.15-0.30\,Ω_b$ at $z=0.5$, and $0.03-0.04\,Ω_b$ at $z=0.8$. These estimates are likely lower bounds, particularly at $z>0.5$, due to the limited number of identified filaments and localized FRBs at higher redshifts. We also examine various factors that may affect the statistical significance of our results. Our method offers an independent approach to tracing baryons in cosmic filaments and underscores the importance of expanding localized FRB samples and deepening galaxy surveys, which are key steps toward refining these estimates and addressing the missing baryon problem.