{"date_created":"2026-01-25T23:01:39Z","volume":545,"oa":1,"ddc":["520"],"_id":"21038","publication":"Monthly Notices of the Royal Astronomical Society","department":[{"_id":"JoMa"}],"arxiv":1,"date_updated":"2026-02-12T12:56:33Z","citation":{"short":"S.J. Chang, M. Gronke, J.J. Matthee, C. Mason, Monthly Notices of the Royal Astronomical Society 545 (2026).","apa":"Chang, S. J., Gronke, M., Matthee, J. J., &#38; Mason, C. (2026). Impact of resonance, Raman, and Thomson scattering on hydrogen line formation in Little Red Dots. <i>Monthly Notices of the Royal Astronomical Society</i>. Oxford University Press. <a href=\"https://doi.org/10.1093/mnras/staf2131\">https://doi.org/10.1093/mnras/staf2131</a>","ama":"Chang SJ, Gronke M, Matthee JJ, Mason C. Impact of resonance, Raman, and Thomson scattering on hydrogen line formation in Little Red Dots. <i>Monthly Notices of the Royal Astronomical Society</i>. 2026;545(4). doi:<a href=\"https://doi.org/10.1093/mnras/staf2131\">10.1093/mnras/staf2131</a>","ieee":"S. J. Chang, M. Gronke, J. J. Matthee, and C. Mason, “Impact of resonance, Raman, and Thomson scattering on hydrogen line formation in Little Red Dots,” <i>Monthly Notices of the Royal Astronomical Society</i>, vol. 545, no. 4. Oxford University Press, 2026.","mla":"Chang, Seok Jun, et al. “Impact of Resonance, Raman, and Thomson Scattering on Hydrogen Line Formation in Little Red Dots.” <i>Monthly Notices of the Royal Astronomical Society</i>, vol. 545, no. 4, staf2131, Oxford University Press, 2026, doi:<a href=\"https://doi.org/10.1093/mnras/staf2131\">10.1093/mnras/staf2131</a>.","chicago":"Chang, Seok Jun, Max Gronke, Jorryt J Matthee, and Charlotte Mason. “Impact of Resonance, Raman, and Thomson Scattering on Hydrogen Line Formation in Little Red Dots.” <i>Monthly Notices of the Royal Astronomical Society</i>. Oxford University Press, 2026. <a href=\"https://doi.org/10.1093/mnras/staf2131\">https://doi.org/10.1093/mnras/staf2131</a>.","ista":"Chang SJ, Gronke M, Matthee JJ, Mason C. 2026. Impact of resonance, Raman, and Thomson scattering on hydrogen line formation in Little Red Dots. Monthly Notices of the Royal Astronomical Society. 545(4), staf2131."},"article_number":"staf2131","file_date_updated":"2026-02-12T12:44:33Z","scopus_import":"1","OA_type":"gold","acknowledgement":"The authorsthank the anonymousreferee for constructive comments, which improved the clarity of this paper. SJC acknowledges support from the ERC synergy grant 101166930 – RECAP. MG thanks the Max Planck Society for support through the Max Planck Research Group, and the European Union forsupport through ERC-2024-STG 101165038 (ReMMU). JM acknowledges funding by the European Union (ERC, AGENTS, 101076224). CAM acknowledges support\r\nby the European Union ERC grant RISES (101163035), Carlsberg Foundation (CF22-1322), and VILLUM FONDEN (37459). Computations were performed on HPC systems Freya and Orion at the Max Planck Computing and Data Facility.","month":"02","has_accepted_license":"1","external_id":{"arxiv":["2508.08768"]},"article_type":"original","status":"public","quality_controlled":"1","abstract":[{"lang":"eng","text":"Little Red Dots (LRDs) are compact sources at z > 5 discovered through James Webb Space Telescope spectroscopy. Their spectra exhibit broad Balmer emission lines (>~1000 km s^−1), alongside absorption features and a pronounced Balmer break – evidence for a dense, neutral hydrogen medium, in which the n = 2 state is significantly populated. When interpreted as arising\r\nfrom active galactic nucleus broad-line regions, inferred black hole masses from local scaling relations exceed expectations given their stellar masses, challenging models of early black hole–galaxy co-evolution. However, radiative transfer effects in dense media may also impact the formation of hydrogen emission lines. We model three scattering processes shaping hydrogen\r\nline profiles: resonance scattering by hydrogen in the n = 2 state, Raman scattering of ultraviolet (UV) radiation by ground-state hydrogen, and Thomson scattering by free electrons. Using 3D Monte Carlo radiative transfer simulations, we examine their imprint on line shapes and ratios. Resonance scattering produces strong deviations from Case B flux ratios, clear differences\r\nbetween Hα and Hβ, and encodes gas kinematics in line profiles but cannot broaden Hβ due to conversion to Paα. While Raman scattering can yield broad wings, scattering of the UV continuum is disfavoured given the absence of strong full width at half-maximum variations across transitions. Raman scattering of higher Lyman-series emission can produce Hα/Hβ wing\r\nwidth ratios of  >~1.28, agreeing with observations. Thomson scattering can reproduce the observed >~ 1000 km s^−1 wings under plausible conditions – e.g. Te ∼ 10^4 K and Ne ∼ 10^24 cm^−2 – and lead to black hole mass overestimates by factors  10. Our results provide a framework for interpreting hydrogen lines in LRDs and similar systems."}],"project":[{"_id":"bd9b2118-d553-11ed-ba76-db24564edfea","name":"Young galaxies as tracers and agents of cosmic reionization","grant_number":"101076224"}],"intvolume":"       545","year":"2026","publisher":"Oxford University Press","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","doi":"10.1093/mnras/staf2131","OA_place":"publisher","language":[{"iso":"eng"}],"author":[{"first_name":"Seok Jun","full_name":"Chang, Seok Jun","last_name":"Chang"},{"last_name":"Gronke","first_name":"Max","full_name":"Gronke, Max"},{"id":"7439a258-f3c0-11ec-9501-9df22fe06720","last_name":"Matthee","first_name":"Jorryt J","full_name":"Matthee, Jorryt J","orcid":"0000-0003-2871-127X"},{"full_name":"Mason, Charlotte","first_name":"Charlotte","last_name":"Mason"}],"file":[{"success":1,"date_updated":"2026-02-12T12:44:33Z","file_id":"21220","relation":"main_file","file_name":"2026_MonthNoticesRAS_Chang.pdf","checksum":"52ba7d7b5b80af0c50f57e4c2acc3930","date_created":"2026-02-12T12:44:33Z","file_size":5600366,"creator":"dernst","content_type":"application/pdf","access_level":"open_access"}],"publication_status":"published","type":"journal_article","issue":"4","tmp":{"short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png"},"title":"Impact of resonance, Raman, and Thomson scattering on hydrogen line formation in Little Red Dots","article_processing_charge":"Yes","PlanS_conform":"1","publication_identifier":{"issn":["0035-8711"],"eissn":["1365-2966"]},"DOAJ_listed":"1","oa_version":"Published Version","date_published":"2026-02-01T00:00:00Z","day":"01"}