{"about":{"site":"https://codewithpapers.app","non_affiliation":"Code with Papers and Syntology are not affiliated with, endorsed by, or sponsored by Papers with Code, Meta, or the pwc-archive mirror.","licence":"CC BY-SA 4.0","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","attribution":"https://codewithpapers.app/attribution","modified":"archive material modified by Syntology; see the attribution page"},"url":"/paper/a-method-to-determine-the-evolution-history","title":"A method to determine the evolution history of the mean neutral Hydrogen fraction","arxiv_id":"1810.06273","date":"2018-10-15","proceeding":null,"authors":["Rajesh Mondal","Somnath Bharadwaj","Ilian T. Iliev","Kanan K. Datta","Suman Majumdar","Abinash K. Shaw","Anjan K. Sarkar"],"abstract":"The light-cone (LC) effect imprints the cosmological evolution of the redshifted 21-cm signal $T_{\\rm b} ({\\hat{\\bf{n}}}, \\nu)$ along the frequency axis which is the line of sight (LoS) direction of an observer. The effect is particularly pronounced during the Epoch of Reionization (EoR) when the mean hydrogen neutral fraction ${\\bar{x}_{\\rm HI}}(\\nu)$ falls rapidly as the universe evolves. The multi-frequency angular power spectrum (MAPS) ${{\\mathcal C}_{\\ell}}(\\nu_1,\\nu_2)$ quantifies the entire second-order statistics of $T_{\\rm b} ({\\hat{\\bf{n}}}, \\nu)$ considering both the systematic variation along $\\nu$ due to the cosmological evolution and also the statistically homogeneous and isotropic fluctuations along all the three spatial directions encoded in ${\\hat{\\bf{n}}}$ and $\\nu$. Here we propose a simple model where the systematic frequency $(\\nu_1,\\nu_2)$ dependence of ${{\\mathcal C}_{\\ell}}(\\nu_1,\\nu_2)$ arises entirely due to the evolution of ${\\bar{x}_{\\rm HI}}(\\nu)$. This provides a new method to observationally determine the reionization history. Considering a LC simulation of the EoR 21-cm signal, we use the diagonal elements $\\nu_1=\\nu_2$ of ${{\\mathcal C}_{\\ell}}(\\nu_1,\\nu_2)$ to validate our model. We demonstrate that it is possible to recover the reionization history across the entire observational bandwidth provided we have the value ${\\bar{x}_{\\rm HI}}$ at a single frequency as an external input.","url_abs":"http://arxiv.org/abs/1810.06273v3","url_pdf":"http://arxiv.org/pdf/1810.06273v3.pdf","source":{"archive":"pwc-archive (Hugging Face), CC BY-SA 4.0","snapshot":"2025-07-28","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","row_kind":"links_only","authors_date_abstract":"arXiv metadata, CC0 1.0 (https://info.arxiv.org/help/license), from the Kaggle arXiv metadata snapshot of 2026-09-12"},"code_links":[{"paper_slug":"a-method-to-determine-the-evolution-history","repo_url":"https://github.com/rajeshmondal18/MAPS","is_official":1,"mentioned_in_paper":0,"mentioned_in_github":0,"framework":"none","reach":null}],"tasks":[],"methods":[],"datasets_introduced":[],"methods_introduced":[],"results":[],"syntology":{"atlas_url":null,"mcp":null,"developers":"https://syntology.ai/developers"},"arxiv_metadata":null,"syntology_extracted_results":null}