A large thermal energy reservoir in the nascent intracluster medium at a redshift of 4.3

A large thermal energy reservoir in the nascent intracluster medium at a redshift of 4.3 | 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 Physical Sciences - Article A large thermal energy reservoir in the nascent intracluster medium at a redshift of 4.3 Dazhi Zhou, Scott Chapman, Manuel Aravena, Pablo Araya-Araya, and 20 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7127690/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 05 Jan, 2026 Read the published version in Nature → Version 1 posted You are reading this latest preprint version Abstract Most baryons in present-day galaxy clusters exist as hot gas (≳10^7K), forming the intracluster medium (ICM) [1]. Cosmological simulations predict that the mass and temperature of the ICM rapidly decrease with increasing cosmological redshift, as intracluster gas in younger clusters is still accumulating and being heated [2–4]. The thermal Sunyaev-Zeldovich (tSZ) effect arises when cosmic microwave background (CMB) photons are scattered to higher energies through interactions with energetic electrons in hot ICM, leaving a localized decrement in the CMB at a long wavelength [5, 6]. The depth of this decrement is a measure of the thermal energy and pressure of the gas [7]. To date, the effect has been detected in only three systems at or above z~2, when the Universe was 4 billion years old, making the time and mechanism of ICM assembly uncertain [8–10]. Here, we report observations of this effect in the protocluster SPT2349−56 with Atacama Large Millimeter/submillimeter Array (ALMA). SPT2349−56 contains a large molecular gas reservoir, with at least 30 dusty star-forming galaxies (DSFGs) and three radio-loud active galactic nuclei (AGN) in a 100-kpc region at z=4.3, corresponding to 1.4 billion years after the Big Bang [11–14]. The observed tSZ signal implies a thermal energy of 10^61 erg, exceeding the possible energy of a virialized ICM by an order of magnitude. Contrary to current theoretical expectations [3, 4, 15], the strong tSZ decrement in SPT2349−56 demonstrates that substantial heating can occur and deposit a large amount of thermal energy within growing galaxy clusters, overheating the nascent ICM in unrelaxed structures, two billion years before the first mature clusters emerged at z 2. Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Galaxies and clusters Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Early universe Full Text Additional Declarations There is NO Competing Interest. Cite Share Download PDF Status: Published Journal Publication published 05 Jan, 2026 Read the published version in Nature → 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-7127690","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Physical Sciences - Article","associatedPublications":[],"authors":[{"id":486243470,"identity":"10a070dc-55d2-4f2d-9da6-3cee66f97a73","order_by":0,"name":"Dazhi 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