The Cosmic Baryon Census, Updated: Reservoir-by-Reservoir Accounting and Closure by Fast Radio Burst Dispersion Measures

The total density of ordinary (baryonic) matter is measured precisely at early times, but the inventory of that matter in the nearby universe was long incomplete. We present an updated low-redshift census in the tradition of Fukugita and Peebles (2004), using the reservoir fractions of Shull, Smith and Danforth (2012) as cited inputs and performing all derived arithmetic in an accompanying reproducible script. The Planck value Omega_b h^2 = 0.0224 +- 0.0001, with H_0 = 67.4 +- 0.5 km s^-1 Mpc^-1, gives Omega_b = 0.04931 +- 0.00076 and a mean baryon density today of 4.21 x 10^-31 g cm^-3, corresponding to a hydrogen number density of 1.89 x 10^-7 cm^-3. Summing six reservoirs - stars in galaxies (7 +- 2 per cent), cold gas (1.7 +- 0.4 per cent), hot intracluster gas (4.0 +- 1.5 per cent), the circumgalactic medium (5 +- 3 per cent), the photoionized Lyman-alpha forest (28 +- 11 per cent), and the warm-hot intergalactic medium traced by O VI and broad Lyman-alpha absorption (25 +- 8 per cent) - accounts for 70.7 +- 14.2 per cent of the baryons, leaving a residual of 29.3 per cent. This reproduces, within rounding, the 29 +- 13 per cent shortfall quoted by Shull et al. (2012), and it lies inside the classic missing-baryon range of roughly 30 to 50 per cent discussed in the literature. Adding the hotter warm-hot phase at T >= 10^6 K, estimated at about 15 per cent from simulations and bracketed at 9 to 40 per cent by O VII absorption results, raises the accounted fraction to 85.7 per cent nominally (79.7 to 110.7 per cent over that bracket), leaving a nominal residual of 14.3 per cent. Independently, dispersion measures of localized fast radio bursts measure the total ionized baryon column directly: Macquart et al. (2020) obtained a cosmic baryon density whose ratio to the Planck value is 1.074, with a 95 per cent range of 0.548 to 1.516 for their sample, and a later 22-burst analysis gives a ratio of 1.072 with a range of 1.000 to 1.151. The dispersion-measure accounting therefore closes the historical gap in the sense that its nominal total equals or exceeds the early-universe total, with no statistically required residual, while a direct reservoir-by-reservoir sum still leaves about 14 per cent nominally unattributed to a specific detected phase. Ranges are carried as ranges throughout; no reservoir fraction is collapsed beyond what its source states.