The Lumina Project: Morphology of Ionized Bubbles and Neutral Islands
Abstract
The Epoch of Reionization is characterized by the nucleation, expansion, and percolation of ionized bubbles in the intergalactic medium. Interpreting emerging multi-wavelength observations from facilities such as JWST and next-generation 21 cm interferometers requires a detailed theoretical understanding of the 3D morphology of these HII regions and of the residual neutral structures that survive near the end of reionization. We analyze the geometry and physical properties of ionized bubbles and late-time neutral islands in the large-volume 500 Mpc3 radiation-hydrodynamics simulation Lumina. We identify discrete structures with a 3D watershed method and measure their volumes, shape tensors, and internal gas properties. The volume-weighted bubble size distributions evolve substantially across the EoR: characteristic radii shift from Reff~1 cMpc at z>10 to Reff>100 cMpc by z< 6, while watershed-derived sizes exceed line-of-sight mean-free-path measurements by roughly a factor of 3 at intermediate redshifts. The bulk bubble population is predominantly prolate through most of the EoR. By z~6, however, the volume-weighted distribution of the triaxiality parameter T, which distinguishes flattened from elongated structures, becomes bimodal in the fiducial segmentation, with a sharp oblate peak near T~0.25 associated with a small number of very large bubbles during late percolation. The properties of bubble interiors are consistent with inside-out reionization, with median gas overdensities within bubbles decreasing from δ~1 at z=15 toward the cosmic mean by z=6. Beyond a minimum near the resolution scale, the median internal UV radiation energy density increases with bubble size. The residual neutral islands at z< 6 peak in volume-weighted size near Reff~10 cMpc and remain predominantly prolate, consistent with anisotropic residual neutral structure near the end of reionization.
Related
- Impact of Residual Gain Errors on the Detectability of Ionized Bubbles during Reionization with SKA 21-cm observations
- Observing Co-Located Neutral and Ionized Gas-Phase Iron Depletion in the Magellanic Clouds
- Observing Colocated Neutral and Ionized Gas-phase Iron Depletion in the Magellanic Clouds
- The VariableTNG project: Mass-dependent regulation of galaxy morphology by baryonic feedback
- The Neutral Atomic Hydrogen in the solar neighborhood (NeAtHood) project
BibTeX
@misc{neyer2026lumina,
title = {{The Lumina Project: Morphology of Ionized Bubbles and Neutral Islands}},
author = {Meredith Neyer and Aaron Smith and Ali Sadain and Oliver Zier and Mark Vogelsberger and Teodora-Elena Bulichi and Xuejian Shen and Sonja M. Koehler and Volker Springel and Rahul Kannan and Rongrong Liu and Lars Hernquist and Changhyun Cho},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.28390},
eprint = {2609.28390},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.28390},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The Lumina Project: Morphology of Ionized Bubbles and Neutral Islands
AU - Meredith Neyer
AU - Aaron Smith
AU - Ali Sadain
AU - Oliver Zier
AU - Mark Vogelsberger
AU - Teodora-Elena Bulichi
AU - Xuejian Shen
AU - Sonja M. Koehler
AU - Volker Springel
AU - Rahul Kannan
AU - Rongrong Liu
AU - Lars Hernquist
AU - Changhyun Cho
PY - 2026
DA - 2026/09/23
PB - arXiv
DO - 10.48550/arxiv.2609.28390
UR - https://arxiv.org/abs/2609.28390
AB - The Epoch of Reionization is characterized by the nucleation, expansion, and percolation of ionized bubbles in the intergalactic medium. Interpreting emerging multi-wavelength observations from facilities such as JWST and next-generation 21 cm interferometers requires a detailed theoretical understanding of the 3D morphology of these HII regions and of the residual neutral structures that survive near the end of reionization. We analyze the geometry and physical properties of ionized bubbles and late-time neutral islands in the large-volume 500 Mpc^3 radiation-hydrodynamics simulation Lumina. We identify discrete structures with a 3D watershed method and measure their volumes, shape tensors, and internal gas properties. The volume-weighted bubble size distributions evolve substantially across the EoR: characteristic radii shift from Reff~1 cMpc at z>10 to Reff>100 cMpc by z< 6, while watershed-derived sizes exceed line-of-sight mean-free-path measurements by roughly a factor of 3 at intermediate redshifts. The bulk bubble population is predominantly prolate through most of the EoR. By z~6, however, the volume-weighted distribution of the triaxiality parameter T, which distinguishes flattened from elongated structures, becomes bimodal in the fiducial segmentation, with a sharp oblate peak near T~0.25 associated with a small number of very large bubbles during late percolation. The properties of bubble interiors are consistent with inside-out reionization, with median gas overdensities within bubbles decreasing from δ~1 at z=15 toward the cosmic mean by z=6. Beyond a minimum near the resolution scale, the median internal UV radiation energy density increases with bubble size. The residual neutral islands at z< 6 peak in volume-weighted size near Reff~10 cMpc and remain predominantly prolate, consistent with anisotropic residual neutral structure near the end of reionization.
ER -