The THESAN project: Lyman-alpha intensity mapping of cosmic reionization
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| Format: | Preprint |
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2025
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| _version_ | 1866908695387963392 |
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| author | Almualla, Mouza Smith, Aaron Kannan, Rahul Hernquist, Lars Garaldi, Enrico Lidz, Adam Lorinc, Kevin Chan, Jennifer Yik Ham Vogelsberger, Mark |
| author_facet | Almualla, Mouza Smith, Aaron Kannan, Rahul Hernquist, Lars Garaldi, Enrico Lidz, Adam Lorinc, Kevin Chan, Jennifer Yik Ham Vogelsberger, Mark |
| contents | Line Intensity Mapping (LIM) has garnered attention as a powerful cosmological probe, with next-generation instruments such as SPHEREx preparing to map the evolution of large-scale structure during the Epoch of Reionization (EoR). Lyman-alpha emission in the EoR is strongly shaped by resonant absorption from neutral hydrogen in the diffuse intergalactic medium (IGM), which transforms galactic sources into a low surface-brightness background. In this work, we leverage the state-of-the-art THESAN cosmological simulations to produce high-resolution theoretical predictions for future Lyman-alpha LIM studies, constructing continuous light cones for line-of-sight cosmological integrations. We assess the contributions of recombination, collisional excitation, and unresolved HII regions to the total Lyman-alpha spectral intensity. In addition, we explore the IGM in absorption at different redshifts using damping wing analysis. We produce channel maps exploring spatial fluctuations across redshift bands probe-able by LIM instruments. We find that the slope of the absorption-included Lyman-alpha fluctuation power spectrum at smaller scales (k > 10^(-2) 1/arcsec) steepens toward lower redshift, and that our emission-only Lyman-alpha power spectrum lies above the SPHEREx sensitivity, whereas the absorption-included signal is ~4 orders of magnitude lower--providing a conservative lower limit on inhomogeneity signatures and highlighting the importance of including resonant scattering in our model in the future. We also find that including outflows in a simple toy model boosts power by four orders of magnitude. We identify limitations in our analysis and propose next steps, including incorporating the effects of resonant Lyman-alpha scattering and line interlopers, as well as larger simulation volumes. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2512_06085 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The THESAN project: Lyman-alpha intensity mapping of cosmic reionization Almualla, Mouza Smith, Aaron Kannan, Rahul Hernquist, Lars Garaldi, Enrico Lidz, Adam Lorinc, Kevin Chan, Jennifer Yik Ham Vogelsberger, Mark Cosmology and Nongalactic Astrophysics Line Intensity Mapping (LIM) has garnered attention as a powerful cosmological probe, with next-generation instruments such as SPHEREx preparing to map the evolution of large-scale structure during the Epoch of Reionization (EoR). Lyman-alpha emission in the EoR is strongly shaped by resonant absorption from neutral hydrogen in the diffuse intergalactic medium (IGM), which transforms galactic sources into a low surface-brightness background. In this work, we leverage the state-of-the-art THESAN cosmological simulations to produce high-resolution theoretical predictions for future Lyman-alpha LIM studies, constructing continuous light cones for line-of-sight cosmological integrations. We assess the contributions of recombination, collisional excitation, and unresolved HII regions to the total Lyman-alpha spectral intensity. In addition, we explore the IGM in absorption at different redshifts using damping wing analysis. We produce channel maps exploring spatial fluctuations across redshift bands probe-able by LIM instruments. We find that the slope of the absorption-included Lyman-alpha fluctuation power spectrum at smaller scales (k > 10^(-2) 1/arcsec) steepens toward lower redshift, and that our emission-only Lyman-alpha power spectrum lies above the SPHEREx sensitivity, whereas the absorption-included signal is ~4 orders of magnitude lower--providing a conservative lower limit on inhomogeneity signatures and highlighting the importance of including resonant scattering in our model in the future. We also find that including outflows in a simple toy model boosts power by four orders of magnitude. We identify limitations in our analysis and propose next steps, including incorporating the effects of resonant Lyman-alpha scattering and line interlopers, as well as larger simulation volumes. |
| title | The THESAN project: Lyman-alpha intensity mapping of cosmic reionization |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2512.06085 |