{"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/constraining-the-contribution-of-active","title":"Constraining the contribution of active galactic nuclei to reionisation","arxiv_id":"1705.05398","date":"2017-05-15","proceeding":null,"authors":["Sultan Hassan","Romeel Davé","Sourav Mitra","Kristian Finlator","Benedetta Ciardi","Mario G. Santos"],"abstract":"Recent results have suggested that active galactic nuclei (AGN) could provide enough photons to reionise the Universe. We assess the viability of this scenario using a semi-numerical framework for modeling reionisation, to which we add a quasar contribution by constructing a Quasar Halo Occupation Distribution (QHOD) based on Giallongo et al. observations. Assuming a constant QHOD, we find that an AGN-only model cannot simultaneously match observations of the optical depth $\\tau_e$, neutral fraction, and ionising emissivity. Such a model predicts $\\tau_e$ too low by $\\sim 2\\sigma$ relative to Planck constraints, and reionises the Universe at $z\\lesssim 5$. Arbitrarily increasing the AGN emissivity to match these results yields a strong mismatch with the observed ionising emissivity at $z\\sim 5$. If we instead assume a redshift-independent AGN luminosity function yielding an emissivity evolution like that assumed in Madau & Haardt model, then we can match $\\tau_e$ albeit with late reionisation, however such evolution is inconsistent with observations at $z\\sim 4-6$ and poorly motivated physically. These results arise because AGN are more biased towards massive halos than typical reionising galaxies, resulting in stronger clustering and later formation times. AGN-dominated models produce larger ionising bubbles that are reflected in $\\sim\\times 2$ more 21cm power on all scales. A model with equal parts galaxies and AGN contribution is still (barely) consistent with observations, but could be distinguished using next-generation 21cm experiments HERA and SKA-low. We conclude that, even with recent claims of more faint AGN than previously thought, AGN are highly unlikely to dominate the ionising photon budget for reionisation.","url_abs":"https://arxiv.org/abs/1705.05398v2","url_pdf":"https://arxiv.org/pdf/1705.05398v2.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":"constraining-the-contribution-of-active","repo_url":"https://github.com/sultan-hassan/Simfast21_Galaxies_AGN","is_official":0,"mentioned_in_paper":0,"mentioned_in_github":1,"framework":"none","reach":null}],"tasks":[],"methods":[],"datasets_introduced":[],"methods_introduced":[],"results":[],"syntology":{"syntology_url":null,"atlas_url":null,"mcp":null,"developers":"https://syntology.ai/developers"},"arxiv_metadata":null,"syntology_extracted_results":null}