{"acknowledgement":"We thank the referee for their constructive comments that helped to improve the paper. We thank Junyao Li for sharing model output shown in Figure 13, Rob Crain for sharing results from the ONLYAGN EAGLE model shown in Figure 15, and Adi Zitrin for comments. This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with programs # 3516. Funded by the European Union (ERC, AGENTS, 101076224). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. We acknowledge funding from JWST program GO-3516. Support for this work was provided by NASA through the NASA Hubble Fellowship grant HST-HF2-51515.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS 5-26555. A.A. acknowledges support by the Swedish research council Vetenskapsrådet (2021-05559).","status":"public","date_published":"2025-07-29T00:00:00Z","file_date_updated":"2026-02-09T08:20:14Z","quality_controlled":"1","abstract":[{"lang":"eng","text":"JWST observations have unveiled faint active galactic nuclei (AGNs) at high redshift that provide insights into the formation of supermassive black holes (SMBHs). However, disentangling their stellar from AGN light is challenging. Here, we use an empirical approach to infer the average stellar mass of five faint broad-line (BL) Hα emitters at z = 4–5 with BH masses ≈6 × 10^6 M⊙, with a method independent of their spectral energy distribution (SED). We use the deep JWST/NIRcam grism survey “All the Little Things” to measure the overdensities around BL-Hα emitters and around a spectroscopic reference sample of ∼300 galaxies. In our reference sample, we find that megaparsec-scale overdensity correlates with stellar mass. Their large-scale environments suggest that BL-Hα emitters are hosted by galaxies with stellar masses ≈5 × 10^7 M⊙, ≈40 times lower than those inferred from galaxy-only SED fits. Adding measurements around more luminous z ≈ 6 AGNs, we find tentative correlations between line width, BH mass, and the overdensity, suggestive of a steep BH to halo mass relation. The main implications are (1) when BH masses are taken at face value, we confirm extremely high BH to stellar mass ratios of ≈10%, (2) the galaxies of low stellar mass that host growing SMBHs are in tension with typical hydrodynamical simulations, except those without feedback, (3) a 1% duty cycle implied by the host mass hints at super-Eddington accretion, (4) the masses are at odds with an interpretation of the line broadening in terms of high stellar density, (5) our results imply a luminosity-dependent diversity of galaxy masses, environments, and SEDs among AGN samples."}],"OA_type":"gold","OA_place":"publisher","month":"07","title":"Environmental evidence for overly massive Black Holes in low-mass galaxies and a Black Hole–Halo mass relation at z ∼ 5","language":[{"iso":"eng"}],"oa":1,"arxiv":1,"ddc":["520"],"_id":"21062","citation":{"short":"J.J. Matthee, R.P. Naidu, G. Kotiwale, L.J. Furtak, I. Kramarenko, R. Mackenzie, J. Greene, A. Adamo, R.J. Bouwens, C. Di Cesare, A.-C. Eilers, A. de Graaff, K.E. Heintz, D. Kashino, M.V. Maseda, S. Tacchella, A. Torralba Torregrosa, The Astrophysical Journal 988 (2025).","chicago":"Matthee, Jorryt J, Rohan P. Naidu, Gauri Kotiwale, Lukas J. Furtak, Ivan Kramarenko, Ruari Mackenzie, Jenny Greene, et al. “Environmental Evidence for Overly Massive Black Holes in Low-Mass Galaxies and a Black Hole–Halo Mass Relation at z ∼ 5.” <i>The Astrophysical Journal</i>. IOP Publishing, 2025. <a href=\"https://doi.org/10.3847/1538-4357/ade886\">https://doi.org/10.3847/1538-4357/ade886</a>.","ama":"Matthee JJ, Naidu RP, Kotiwale G, et al. Environmental evidence for overly massive Black Holes in low-mass galaxies and a Black Hole–Halo mass relation at z ∼ 5. <i>The Astrophysical Journal</i>. 2025;988(2). doi:<a href=\"https://doi.org/10.3847/1538-4357/ade886\">10.3847/1538-4357/ade886</a>","mla":"Matthee, Jorryt J., et al. “Environmental Evidence for Overly Massive Black Holes in Low-Mass Galaxies and a Black Hole–Halo Mass Relation at z ∼ 5.” <i>The Astrophysical Journal</i>, vol. 988, no. 2, 246, IOP Publishing, 2025, doi:<a href=\"https://doi.org/10.3847/1538-4357/ade886\">10.3847/1538-4357/ade886</a>.","ieee":"J. J. Matthee <i>et al.</i>, “Environmental evidence for overly massive Black Holes in low-mass galaxies and a Black Hole–Halo mass relation at z ∼ 5,” <i>The Astrophysical Journal</i>, vol. 988, no. 2. IOP Publishing, 2025.","ista":"Matthee JJ, Naidu RP, Kotiwale G, Furtak LJ, Kramarenko I, Mackenzie R, Greene J, Adamo A, Bouwens RJ, Di Cesare C, Eilers A-C, de Graaff A, Heintz KE, Kashino D, Maseda MV, Tacchella S, Torralba Torregrosa A. 2025. Environmental evidence for overly massive Black Holes in low-mass galaxies and a Black Hole–Halo mass relation at z ∼ 5. The Astrophysical Journal. 988(2), 246.","apa":"Matthee, J. J., Naidu, R. P., Kotiwale, G., Furtak, L. J., Kramarenko, I., Mackenzie, R., … Torralba Torregrosa, A. (2025). Environmental evidence for overly massive Black Holes in low-mass galaxies and a Black Hole–Halo mass relation at z ∼ 5. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ade886\">https://doi.org/10.3847/1538-4357/ade886</a>"},"issue":"2","file":[{"content_type":"application/pdf","date_created":"2026-02-09T08:20:14Z","file_id":"21168","date_updated":"2026-02-09T08:20:14Z","file_name":"2025_AstrophysicalJournal_Matthee.pdf","success":1,"creator":"dernst","access_level":"open_access","file_size":6237415,"relation":"main_file","checksum":"a49fbed72f2ff9c0b13129acb6f44f9d"}],"article_number":"246","project":[{"name":"Young galaxies as tracers and agents of cosmic reionization","grant_number":"101076224","_id":"bd9b2118-d553-11ed-ba76-db24564edfea"}],"tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"external_id":{"arxiv":["2412.02846"]},"PlanS_conform":"1","DOAJ_listed":"1","year":"2025","has_accepted_license":"1","oa_version":"Published Version","corr_author":"1","publisher":"IOP Publishing","author":[{"last_name":"Matthee","first_name":"Jorryt J","id":"7439a258-f3c0-11ec-9501-9df22fe06720","orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J"},{"last_name":"Naidu","first_name":"Rohan P.","full_name":"Naidu, Rohan P."},{"full_name":"Kotiwale, Gauri","id":"1438afc8-1ff6-11ee-9fa6-cd4a75d66875","first_name":"Gauri","last_name":"Kotiwale"},{"first_name":"Lukas J.","last_name":"Furtak","full_name":"Furtak, Lukas J."},{"full_name":"Kramarenko, Ivan","orcid":"0000-0001-5346-6048","id":"9a9394cb-3200-11ee-973b-f5ba2a8b16e4","first_name":"Ivan","last_name":"Kramarenko"},{"full_name":"Mackenzie, Ruari","first_name":"Ruari","last_name":"Mackenzie"},{"full_name":"Greene, Jenny","last_name":"Greene","first_name":"Jenny"},{"full_name":"Adamo, Angela","first_name":"Angela","last_name":"Adamo"},{"last_name":"Bouwens","first_name":"Rychard J.","full_name":"Bouwens, Rychard J."},{"id":"2d002343-372f-11ef-98ec-a164d20427cb","first_name":"Claudia","last_name":"Di Cesare","full_name":"Di Cesare, Claudia"},{"last_name":"Eilers","first_name":"Anna-Christina","full_name":"Eilers, Anna-Christina"},{"full_name":"de Graaff, Anna","last_name":"de Graaff","first_name":"Anna"},{"last_name":"Heintz","first_name":"Kasper E.","full_name":"Heintz, Kasper E."},{"full_name":"Kashino, Daichi","first_name":"Daichi","last_name":"Kashino"},{"full_name":"Maseda, Michael V.","last_name":"Maseda","first_name":"Michael V."},{"last_name":"Tacchella","first_name":"Sandro","full_name":"Tacchella, Sandro"},{"full_name":"Torralba Torregrosa, Alberto","last_name":"Torralba Torregrosa","first_name":"Alberto","id":"018f0249-0e87-11f0-b167-cbce08fbd541","orcid":"0000-0001-5586-6950"}],"day":"29","intvolume":"       988","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","article_processing_charge":"Yes","publication":"The Astrophysical Journal","type":"journal_article","doi":"10.3847/1538-4357/ade886","department":[{"_id":"JoMa"}],"volume":988,"date_updated":"2026-02-09T08:22:01Z","date_created":"2026-01-28T15:25:42Z","publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]},"scopus_import":"1","publication_status":"published","article_type":"original"}