Astronomy Unit, Department of Physics, University of Trieste, Trieste, Italy.
INAF - Osservatorio Astronomico di Trieste, Trieste, Italy.
Nature. 2023 Mar;615(7954):809-812. doi: 10.1038/s41586-023-05761-x. Epub 2023 Mar 29.
Galaxy clusters are the most massive gravitationally bound structures in the Universe, comprising thousands of galaxies and pervaded by a diffuse, hot intracluster medium (ICM) that dominates the baryonic content of these systems. The formation and evolution of the ICM across cosmic time is thought to be driven by the continuous accretion of matter from the large-scale filamentary surroundings and energetic merger events with other clusters or groups. Until now, however, direct observations of the intracluster gas have been limited only to mature clusters in the later three-quarters of the history of the Universe, and we have been lacking a direct view of the hot, thermalized cluster atmosphere at the epoch when the first massive clusters formed. Here we report the detection (about 6σ) of the thermal Sunyaev-Zeldovich (SZ) effect in the direction of a protocluster. In fact, the SZ signal reveals the ICM thermal energy in a way that is insensitive to cosmological dimming, making it ideal for tracing the thermal history of cosmic structures. This result indicates the presence of a nascent ICM within the Spiderweb protocluster at redshift z = 2.156, around 10 billion years ago. The amplitude and morphology of the detected signal show that the SZ effect from the protocluster is lower than expected from dynamical considerations and comparable with that of lower-redshift group-scale systems, consistent with expectations for a dynamically active progenitor of a local galaxy cluster.
星系团是宇宙中最大的引力束缚结构，包含数千个星系，并且弥漫着一种弥散的、热的星系团内介质（ICM），它主导着这些系统的重子含量。ICM 在宇宙时间内的形成和演化被认为是由来自大尺度丝状环境的物质连续吸积以及与其他星系团或星系群的能量合并事件驱动的。然而，直到现在，对星系内气体的直接观测仅限于宇宙历史后四分之三的成熟星系团，并且我们一直缺乏对第一个大质量星系团形成时的热、热化星系团大气的直接观察。在这里，我们报告了在一个原星系团方向上探测到热 Sunyaev-Zeldovich（SZ）效应（约 6σ）。实际上，SZ 信号以对宇宙学变暗不敏感的方式揭示了 ICM 的热能量，使其成为追踪宇宙结构热历史的理想选择。这一结果表明，在 Spiderweb 原星系团中存在一个初生的 ICM，其红移 z=2.156，大约在 100 亿年前。探测到的信号的幅度和形态表明，原星系团的 SZ 效应低于动力学考虑所预期的，与较低红移的星系团尺度系统相当，这与本地星系团的动态活跃祖星系的预期一致。
