Cosmic Reionization on Computers: The Evolution of the Ionizing Background and Mean Free Path
Observations of the end stages of reionization indicate that at z ≈ 5–6, the ionizing background is not uniform and the mean free path (MFP) changes drastically. As the MFP is closely related to the distribution of Lyman-limit systems (LLSs) and damped Ly α absorbers, it is important to understand...
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IOP Publishing
2025-01-01
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| Online Access: | https://doi.org/10.3847/1538-4357/ada1d3 |
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| author | Jiawen Fan Huanqing Chen Camille Avestruz Affan Khadir |
| author_facet | Jiawen Fan Huanqing Chen Camille Avestruz Affan Khadir |
| author_sort | Jiawen Fan |
| collection | DOAJ |
| description | Observations of the end stages of reionization indicate that at z ≈ 5–6, the ionizing background is not uniform and the mean free path (MFP) changes drastically. As the MFP is closely related to the distribution of Lyman-limit systems (LLSs) and damped Ly α absorbers, it is important to understand them. In this study, we utilize the Cosmic Reionization on Computers (CROC) simulations, which have both sufficient spatial resolution to resolve galaxy formation and LLSs alongside a fully coupled radiative transfer, to simulate the reionization processes. We analyze two CROC boxes with distinct reionization histories and find that the distributions of the ionizing background in both simulations display significant skewness. Further, the ionizing background in the late-reionization box still displays significant fluctuations (∼40%) at z ≈ 5. We also measure the MFP along sightlines that center on potential quasar hosting halos. The evolution of the MFP measured from these sightlines exhibits a break that coincides with the disappearance of all the neutral islands in the reionization history of each box. In the absence of LLSs, the MFP will be biased high by ≈20% at z ≈ 5. We also compare the MFPs measured in random sightlines. We find that at z ≈ 5, the MFPs measured in sightlines that start from massive halos are systematically smaller by ≈10% compared with the MFPs measured in random sightlines. We attribute this difference to the concentration of dense structures within 1 pMpc of massive halos. Our findings highlight the importance of high-fidelity models in the interpretation of observational measurements. |
| format | Article |
| id | doaj-art-4574484e45324499bfe4b692355d2c9f |
| institution | Kabale University |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal |
| spelling | doaj-art-4574484e45324499bfe4b692355d2c9f2025-01-23T08:14:03ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01979215010.3847/1538-4357/ada1d3Cosmic Reionization on Computers: The Evolution of the Ionizing Background and Mean Free PathJiawen Fan0https://orcid.org/0009-0002-9477-886XHuanqing Chen1https://orcid.org/0000-0002-3211-9642Camille Avestruz2https://orcid.org/0000-0001-8868-0810Affan Khadir3https://orcid.org/0009-0001-2196-8251Department of Physics, University of Michigan , Ann Arbor, MI 48109, USA ; johnfan@umich.eduAugustana Campus, University of Alberta , Camrose, AB T4V 2R3, Canada ; hqchen@cita.utoronto.ca; Canadian Institute for Theoretical Astrophysics, University of Toronto , Toronto, ON M5R 2M8, CanadaDepartment of Physics, Leinweber Center for Theoretical Physics, University of Michigan , Ann Arbor, MI 48109, USADepartment of Physics, University of Toronto , Toronto, ON M5R 2M8, CanadaObservations of the end stages of reionization indicate that at z ≈ 5–6, the ionizing background is not uniform and the mean free path (MFP) changes drastically. As the MFP is closely related to the distribution of Lyman-limit systems (LLSs) and damped Ly α absorbers, it is important to understand them. In this study, we utilize the Cosmic Reionization on Computers (CROC) simulations, which have both sufficient spatial resolution to resolve galaxy formation and LLSs alongside a fully coupled radiative transfer, to simulate the reionization processes. We analyze two CROC boxes with distinct reionization histories and find that the distributions of the ionizing background in both simulations display significant skewness. Further, the ionizing background in the late-reionization box still displays significant fluctuations (∼40%) at z ≈ 5. We also measure the MFP along sightlines that center on potential quasar hosting halos. The evolution of the MFP measured from these sightlines exhibits a break that coincides with the disappearance of all the neutral islands in the reionization history of each box. In the absence of LLSs, the MFP will be biased high by ≈20% at z ≈ 5. We also compare the MFPs measured in random sightlines. We find that at z ≈ 5, the MFPs measured in sightlines that start from massive halos are systematically smaller by ≈10% compared with the MFPs measured in random sightlines. We attribute this difference to the concentration of dense structures within 1 pMpc of massive halos. Our findings highlight the importance of high-fidelity models in the interpretation of observational measurements.https://doi.org/10.3847/1538-4357/ada1d3ReionizationIntergalactic medium |
| spellingShingle | Jiawen Fan Huanqing Chen Camille Avestruz Affan Khadir Cosmic Reionization on Computers: The Evolution of the Ionizing Background and Mean Free Path The Astrophysical Journal Reionization Intergalactic medium |
| title | Cosmic Reionization on Computers: The Evolution of the Ionizing Background and Mean Free Path |
| title_full | Cosmic Reionization on Computers: The Evolution of the Ionizing Background and Mean Free Path |
| title_fullStr | Cosmic Reionization on Computers: The Evolution of the Ionizing Background and Mean Free Path |
| title_full_unstemmed | Cosmic Reionization on Computers: The Evolution of the Ionizing Background and Mean Free Path |
| title_short | Cosmic Reionization on Computers: The Evolution of the Ionizing Background and Mean Free Path |
| title_sort | cosmic reionization on computers the evolution of the ionizing background and mean free path |
| topic | Reionization Intergalactic medium |
| url | https://doi.org/10.3847/1538-4357/ada1d3 |
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