Surprising Increase of Electron Temperature in Metal-Rich Star-Forming Regions

Surprising Increase of Electron Temperature in Metal-Rich Star-Forming Regions | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Surprising Increase of Electron Temperature in Metal-Rich Star-Forming Regions Renbin Yan, Ziming Peng, Zesen Lin, Xihan Ji, Man-Yin Leo Lee, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7292848/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Measuring gas-phase metallicity, the relative abundance of elements heavier than helium to the abundance of hydrogen, is essential for constraining the chemical evolution of galaxies. The electron temperature is a crucial parameter for the determination of metallicity as the strongest emission lines from metal ions are all collisionally excited, which depends sensitively on temperature. Electron temperatures can be measured by comparing the strengths of two emission lines of the same ion that originate from two different upper levels, which are usually referred to as auroral-to-strong line ratios. Low electron temperature is theoretically expected for metal-rich star-forming regions, as metal ions in high metallicity gas provide efficient cooling through collisional excitation and radiative de-excitation. In this work, we report the discovery that temperature, as measured through auroral-to-strong line ratios of O + , trends in reverse directions at supersolar metallicities. This trend remains consistent regardless of the emission line fitting method employed and is not attributable to contamination or dust attenuation correction. Notably, this phenomenon is not observed in other low-ionization ions, such as S + and N + , which also probe electron temperature. The results are verified in two independent datasets. This finding challenges the fundamental principles of the direct T e method for metallicity measurement, warranting further investigation into its physical interpretation. Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Interstellar medium Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Galaxies and clusters Full Text Additional Declarations There is NO Competing Interest. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7292848","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":518709638,"identity":"97c56f2f-0a04-44cd-8f13-3f46266e4030","order_by":0,"name":"Renbin 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The electron temperature is a crucial parameter for the determination of metallicity as the strongest emission lines from metal ions are all collisionally excited, which depends sensitively on temperature. Electron temperatures can be measured by comparing the strengths of two emission lines of the same ion that originate from two different upper levels, which are usually referred to as auroral-to-strong line ratios. Low electron temperature is theoretically expected for metal-rich star-forming regions, as metal ions in high metallicity gas provide efficient cooling through collisional excitation and radiative de-excitation. \r\nIn this work, we report the discovery that temperature, as measured through auroral-to-strong line ratios of O\u003csup\u003e+\u003c/sup\u003e, trends in reverse directions at supersolar metallicities. This trend remains consistent regardless of the emission line fitting method employed and is not attributable to contamination or dust attenuation correction. Notably, this phenomenon is not observed in other low-ionization ions, such as S\u003csup\u003e+\u003c/sup\u003e and N\u003csup\u003e+\u003c/sup\u003e, which also probe electron temperature. The results are verified in two independent datasets. This finding challenges the fundamental principles of the direct T\u003csub\u003ee\u003c/sub\u003e method for metallicity measurement, warranting further investigation into its physical interpretation.","manuscriptTitle":"Surprising Increase of Electron Temperature in Metal-Rich Star-Forming Regions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-23 10:11:34","doi":"10.21203/rs.3.rs-7292848/v1","editorialEvents":[{"type":"communityComments","content":2}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a2fb25b8-d7d5-44c9-b0fd-1afa533cb059","owner":[],"postedDate":"September 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":55118102,"name":"Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Interstellar medium"},{"id":55118103,"name":"Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Galaxies and clusters"}],"tags":[],"updatedAt":"2025-10-27T14:16:13+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-23 10:11:34","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7292848","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7292848","identity":"rs-7292848","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}