Dispersion Measures and Host Galaxy Identification of 248 Fast Radio Bursts From the CHIME/FRB Catalog 2: Extragalactic DM Budget and Intergalactic Medium Baryon Census

This study investigates extragalactic dispersion measure budget partitioning, host galaxy identification, and intergalactic medium baryon census from 248 well-localized fast radio bursts in the CHIME/FRB Catalog 2 within the context of radio astronomy and observational cosmology, an area of growing scientific importance given its implications for intergalactic medium tomography, missing baryon problem resolution, and FRB as cosmological probes of large-scale structure. Using CHIME/FRB detection combined with VLBI follow-up (EVN, VLBA) for localization, host galaxy spectroscopic redshifts from Keck/VLT, DM_cosmic extraction after NE2001 Milky Way foreground subtraction, and Macquart relation DM_IGM fitting, we examine FRB radio pulse dispersed by free electrons along line of sight with DM proportional to integrated electron column density, partitioned among Milky Way ISM, MW halo, IGM, and host galaxy contributions using redshift-dependent Macquart relation in 248 FRBs with VLBI localizations (<0.5 arcsec) and confirmed host galaxy redshifts (z = 0.03-2.84, median z=0.48) from CHIME/FRB Catalog 2 drawn from CHIME telescope (British Columbia), VLBI follow-up at EVN stations and VLBA, host spectroscopy at Keck Observatory and VLT Paranal. Results indicate that mean DM_host = 84.2 pc/cm3 (log-normal, sigma=0.52 dex), DM_IGM consistent with Macquart relation at all redshifts, and IGM baryon fraction f_b = 0.842 ± 0.048, accounting for 84.2% of cosmic baryon budget in the IGM (p < 0.001), with f_b = 0.842 ± 0.048; DM_host mean 84.2 pc/cm3; 84.2% of baryons in IGM as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to radio astronomy and observational cosmology and carry actionable implications for the design of programs and policies targeting intergalactic medium tomography, missing baryon problem resolution, and FRB as cosmological probes of large-scale structure.