The Lumina Project: CMB Optical Depth Fluctuations from Patchy Reionization
Fuente:
arXiv
Saved in:
| Main Authors: | , , , , , , , , , , |
|---|---|
| Format: | Preprint |
| Published: |
2026
|
| Subjects: | |
| Online Access: | |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| _version_ | 1866916024610193408 |
|---|---|
| author | Smith, Aaron Zier, Oliver Kannan, Rahul Shen, Xuejian Liu, Rongrong Vogelsberger, Mark Springel, Volker Pakmor, Ruediger Koehler, Sonja M. Hernquist, Lars Neyer, Meredith |
| author_facet | Smith, Aaron Zier, Oliver Kannan, Rahul Shen, Xuejian Liu, Rongrong Vogelsberger, Mark Springel, Volker Pakmor, Ruediger Koehler, Sonja M. Hernquist, Lars Neyer, Meredith |
| contents | Patchy reionization couples the ionized-bubble morphology to the underlying density field, making the CMB Thomson optical depth sensitive to both the global ionization history and anisotropic fluctuations on the sky. Using the large-volume radiation-hydrodynamical Lumina simulation, we compute $τ_{\rm CMB}$ in two ways: (i) from global volume- and mass-weighted ionization histories, and (ii) from explicit line-of-sight integrations through on-the-fly light cones. We find that the sightline-averaged optical depth in the light cone, $\langle τ_{\rm LOS} \rangle = 0.0550$, exceeds the value inferred from a global volume-weighted history, $τ_{{\rm CMB},V} = 0.0515$, by $\approx 7\%$. This enhancement is largely captured by the global mass-weighted prediction, $τ_{{\rm CMB},m} = 0.0544$, indicating that precision comparisons to CMB optical-depth constraints should use mass-weighted electron fractions or explicit light-cone integration rather than volume-weighted ionized fractions alone. The excess optical depth accumulates primarily near $z_{\rm LOS} = 8.0^{+1.9}_{-1.3}$, where the combination of high physical density and strong ionization-field patchiness is greatest. The resulting $τ_{\rm LOS}$ field is non-Gaussian and exhibits $\gtrsim 5\%$ sightline-to-sightline scatter, with fluctuations tracing rare early-ionized overdensities and large-scale structure. Coarse-graining experiments show that smoothing the ionization field on $\gtrsim 3 {\rm cMpc}$ scales suppresses the density-ionization correlation and biases $τ_{\rm CMB}$ low relative to the resolved calculation. Finally, angular power spectra and real-space correlation functions decomposed into HII, HeII, and HeIII auto- and cross-contributions reveal scale-dependent departures from simple hydrogen-helium co-tracing and evolving characteristic scales with redshift. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_18939 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | The Lumina Project: CMB Optical Depth Fluctuations from Patchy Reionization Smith, Aaron Zier, Oliver Kannan, Rahul Shen, Xuejian Liu, Rongrong Vogelsberger, Mark Springel, Volker Pakmor, Ruediger Koehler, Sonja M. Hernquist, Lars Neyer, Meredith Cosmology and Nongalactic Astrophysics Astrophysics of Galaxies Patchy reionization couples the ionized-bubble morphology to the underlying density field, making the CMB Thomson optical depth sensitive to both the global ionization history and anisotropic fluctuations on the sky. Using the large-volume radiation-hydrodynamical Lumina simulation, we compute $τ_{\rm CMB}$ in two ways: (i) from global volume- and mass-weighted ionization histories, and (ii) from explicit line-of-sight integrations through on-the-fly light cones. We find that the sightline-averaged optical depth in the light cone, $\langle τ_{\rm LOS} \rangle = 0.0550$, exceeds the value inferred from a global volume-weighted history, $τ_{{\rm CMB},V} = 0.0515$, by $\approx 7\%$. This enhancement is largely captured by the global mass-weighted prediction, $τ_{{\rm CMB},m} = 0.0544$, indicating that precision comparisons to CMB optical-depth constraints should use mass-weighted electron fractions or explicit light-cone integration rather than volume-weighted ionized fractions alone. The excess optical depth accumulates primarily near $z_{\rm LOS} = 8.0^{+1.9}_{-1.3}$, where the combination of high physical density and strong ionization-field patchiness is greatest. The resulting $τ_{\rm LOS}$ field is non-Gaussian and exhibits $\gtrsim 5\%$ sightline-to-sightline scatter, with fluctuations tracing rare early-ionized overdensities and large-scale structure. Coarse-graining experiments show that smoothing the ionization field on $\gtrsim 3 {\rm cMpc}$ scales suppresses the density-ionization correlation and biases $τ_{\rm CMB}$ low relative to the resolved calculation. Finally, angular power spectra and real-space correlation functions decomposed into HII, HeII, and HeIII auto- and cross-contributions reveal scale-dependent departures from simple hydrogen-helium co-tracing and evolving characteristic scales with redshift. |
| title | The Lumina Project: CMB Optical Depth Fluctuations from Patchy Reionization |
| topic | Cosmology and Nongalactic Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2605.18939 |