Sunyaev-Zeldovich detection of hot intracluster gas at redshift 4.3.
basic_science · Level V
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- Record sourced from PubMed, PMID 41491262.
- Also identified by DOI 10.1038/s41586-025-09901-3.
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Abstract
Most baryons in present-day galaxy clusters exist as hot gas (≳10<sup>7</sup> K), forming the intracluster medium (ICM)<sup>1</sup>. Cosmological simulations predict that the mass and temperature of the ICM decline towards earlier times, as intracluster gas in younger clusters is still assembling and being heated<sup>2-4</sup>. To date, hot ICM has been securely detected only in a few systems at or above z ≈ 2, leaving the timing and mechanism of ICM assembly uncertain<sup>5-7</sup>. Here we report the direct observation of hot intracluster gas via its thermal Sunyaev-Zeldovich signature in the protocluster SPT2349-56 with the Atacama Large Millimeter/submillimeter Array. SPT2349-56 hosts a large molecular gas reservoir and three radio-loud active galactic nuclei (AGN) within an approximately 100-kpc region at z = 4.3 (refs. <sup>8-11</sup>). The measurement implies a thermal energy of about 10<sup>61</sup> erg in the core, about 10 times more than gravity alone should produce. Contrary to current theoretical expectations<sup>3,4,12</sup>, the hot ICM in SPT2349-56 demonstrates that substantial heating can occur very early in cluster assembly, depositing enough energy to overheat the nascent ICM well before mature clusters become common at z ≈ 2.