Lumina Simulation Exposes Why Mass-Weighted Reionization Models Are Essential for CMB Optical Depth Accuracy
Lumina preprint demonstrates patchy reionization boosts CMB tau by 7% via mass-weighted effects and light-cone methods, urging updates to standard analyses for accurate cosmic dawn constraints.
The Lumina Project's radiation-hydrodynamical simulation reveals that patchy reionization produces a 7% excess in line-of-sight CMB optical depth compared to standard volume-weighted estimates, primarily accumulating around z=8 where density and ionization fluctuations peak. This preprint (arXiv:2605.18939) employs explicit light-cone integrations through a large-volume simulation rather than relying solely on global ionization histories, exposing non-Gaussian sightline scatter exceeding 5% that traces rare early overdensities. Original coverage often overlooks how smoothing ionization fields beyond 3 cMpc suppresses density-ionization correlations and biases tau low, a limitation that affects forecasts for next-generation CMB experiments. Cross-referencing with Planck 2018 results (arXiv:1807.06209) shows the mass-weighted tau of 0.0544 aligns better with observed constraints than volume-weighted values, while connections to IllustrisTNG reionization studies highlight evolving scale-dependent HII-HeII contributions missed in power-spectrum-only analyses. These findings underscore that cosmic dawn topology requires resolved, mass-weighted approaches to avoid underestimating the timing of reionization's end stages.
HELIX: Lumina's results imply that current volume-weighted tau assumptions systematically skew reionization timelines, requiring mass-weighted or light-cone methods for reliable cosmic dawn models.
Sources (3)
- [1]Primary Source(https://arxiv.org/abs/2605.18939)
- [2]Planck 2018 Cosmological Parameters(https://arxiv.org/abs/1807.06209)
- [3]Related: IllustrisTNG Reionization Studies(https://arxiv.org/abs/2006.11243)