The CMB optical depth constrains the duration of reionization
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| Autores principales: | , , , , , |
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| Formato: | Preprint |
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2025
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| _version_ | 1866918029927907328 |
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| author | Cain, Christopher Van Engelen, Alexander Croker, Kevin S. Kramer, Darby D'Aloisio, Anson Lopez, Garett |
| author_facet | Cain, Christopher Van Engelen, Alexander Croker, Kevin S. Kramer, Darby D'Aloisio, Anson Lopez, Garett |
| contents | Recently, it was pointed out that invoking a large value of the CMB optical depth, $τ_{\rm CMB} = 0.09$, could help resolve tensions between DESI DR2 BAO data and the CMB. This is larger than the value of $τ_{\rm CMB} = 0.058$ measured from the Planck low-$\ell$ polarization data. Traditionally, $τ_{\rm CMB}$ is thought of as a constraint on reionization's midpoint. However, recent observations and modeling of the Ly$α$ forest of high-$z$ quasars at $5 < z < 6$ have tightly constrained the timing of the last $10-20\%$ of reionization, adding nuance to this interpretation. Here, we point out that fixing reionization's endpoint, in accordance with the latest Ly$α$ forest constraints, renders $τ_{\rm CMB}$ a sensitive probe of the duration of reionization, as well as its midpoint. We compare low and high values of $τ_{\rm CMB}$ to upper limits on the patchy kinematic Sunyaev-Zeldovich (pkSZ) effect, another CMB observable that constrains reionization's duration, and find that a value of $τ_{\rm CMB} = 0.09$ is in $\approx 2σ$ tension with existing limits on the pkSZ from the South Pole Telescope. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2505_15899 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The CMB optical depth constrains the duration of reionization Cain, Christopher Van Engelen, Alexander Croker, Kevin S. Kramer, Darby D'Aloisio, Anson Lopez, Garett Cosmology and Nongalactic Astrophysics Astrophysics of Galaxies Recently, it was pointed out that invoking a large value of the CMB optical depth, $τ_{\rm CMB} = 0.09$, could help resolve tensions between DESI DR2 BAO data and the CMB. This is larger than the value of $τ_{\rm CMB} = 0.058$ measured from the Planck low-$\ell$ polarization data. Traditionally, $τ_{\rm CMB}$ is thought of as a constraint on reionization's midpoint. However, recent observations and modeling of the Ly$α$ forest of high-$z$ quasars at $5 < z < 6$ have tightly constrained the timing of the last $10-20\%$ of reionization, adding nuance to this interpretation. Here, we point out that fixing reionization's endpoint, in accordance with the latest Ly$α$ forest constraints, renders $τ_{\rm CMB}$ a sensitive probe of the duration of reionization, as well as its midpoint. We compare low and high values of $τ_{\rm CMB}$ to upper limits on the patchy kinematic Sunyaev-Zeldovich (pkSZ) effect, another CMB observable that constrains reionization's duration, and find that a value of $τ_{\rm CMB} = 0.09$ is in $\approx 2σ$ tension with existing limits on the pkSZ from the South Pole Telescope. |
| title | The CMB optical depth constrains the duration of reionization |
| topic | Cosmology and Nongalactic Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2505.15899 |