The Lumina Project: Intergalactic Clumping and Recombination Sinks
Abstract
Recombinations during the Epoch of Reionization are intrinsically inhomogeneous, with different regions of the intergalactic medium contributing unevenly depending on their density, temperature, ionization state, and spatial patchiness. We combine the high- and medium-resolution 95.5 cMpc Thesan-1 andh Thesan-2 runs with the significantly larger 500 cMpc Lumina simulation to measure clumping factors and recombination rates consistently across different resolutions and box sizes. We consider the standard ionized hydrogen clumping factor, CHII ≡ ⟨ nHII2⟩/⟨ nHII⟩2, and a recombination-weighted clumping factor, Crec. Despite differences in resolution, volume, and reionization history, the simulations show an approximately universal clumping evolution at the 10-20% level when parametrized by the global ionized fraction xHII rather than by redshift. Across all simulations, Crec remains systematically below CHII, with the discrepancy increasing toward lower redshift as photoheating suppresses recombinations. In \lumina, the density-only prescription overpredicts the instantaneous recombination rate by factors of 1.29 at z≈8 and 1.84 at z≈5, and the cumulative recombination count by a factor of 1.45 by z≈5. Mapping the recombination budget in the joint overdensity-temperature plane reveals that the dominant recombination ridges closely follow simple analytic thermal equilibrium bands. Finally, we introduce a phase-space recombination integral and define a phase-space clumping factor, Cps(Δ,T), which isolates the intrinsic recombination enhancement associated with ionization structure and thermal state at fixed overdensity and temperature.
Versions
Related
- Introducing the Lumina project: large-volume radiation-hydrodynamic simulations of the epochs of hydrogen and helium reionization
- The Lumina Project: Morphology of Ionized Bubbles and Neutral Islands
- The Lumina Project: The Demographics of Active Galactic Nuclei from Quasars to Little Red Dots at z ≥ 3
- The Predicament of Absorption-dominated Reionization. II. Observational Estimate of the Clumping Factor at the End of Reionization
- The phase diagram of the intergalactic medium and the entropy floor of groups and clusters: are clusters born warm?
BibTeX
@misc{sadain2026lumina,
title = {{The Lumina Project: Intergalactic Clumping and Recombination Sinks}},
author = {Ali Sadain and Aaron Smith and Oliver Zier and Hyunbae Park and Teodora-Elena Bulichi and Xuejian Shen and Rahul Kannan and Rongrong Liu and Yuan Bian and Volker Springel and Mark Vogelsberger and Sonja M. Koehler and Lars Hernquist},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2606.18382},
eprint = {2606.18382},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.18382},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The Lumina Project: Intergalactic Clumping and Recombination Sinks
AU - Ali Sadain
AU - Aaron Smith
AU - Oliver Zier
AU - Hyunbae Park
AU - Teodora-Elena Bulichi
AU - Xuejian Shen
AU - Rahul Kannan
AU - Rongrong Liu
AU - Yuan Bian
AU - Volker Springel
AU - Mark Vogelsberger
AU - Sonja M. Koehler
AU - Lars Hernquist
PY - 2026
DA - 2026/10/12
PB - arXiv
DO - 10.48550/arxiv.2606.18382
UR - https://arxiv.org/abs/2606.18382
AB - Recombinations during the Epoch of Reionization are intrinsically inhomogeneous, with different regions of the intergalactic medium contributing unevenly depending on their density, temperature, ionization state, and spatial patchiness. We combine the high- and medium-resolution 95.5 cMpc Thesan-1 andh Thesan-2 runs with the significantly larger 500 cMpc Lumina simulation to measure clumping factors and recombination rates consistently across different resolutions and box sizes. We consider the standard ionized hydrogen clumping factor, C_HII ≡ ⟨ n_HII^2⟩/⟨ n_HII⟩^2, and a recombination-weighted clumping factor, C_rec. Despite differences in resolution, volume, and reionization history, the simulations show an approximately universal clumping evolution at the 10-20% level when parametrized by the global ionized fraction x_HII rather than by redshift. Across all simulations, C_rec remains systematically below C_HII, with the discrepancy increasing toward lower redshift as photoheating suppresses recombinations. In \lumina, the density-only prescription overpredicts the instantaneous recombination rate by factors of 1.29 at z≈8 and 1.84 at z≈5, and the cumulative recombination count by a factor of 1.45 by z≈5. Mapping the recombination budget in the joint overdensity-temperature plane reveals that the dominant recombination ridges closely follow simple analytic thermal equilibrium bands. Finally, we introduce a phase-space recombination integral and define a phase-space clumping factor, C_ps(Δ,T), which isolates the intrinsic recombination enhancement associated with ionization structure and thermal state at fixed overdensity and temperature.
ER -