In order to connect galaxy clusters to their progenitor protoclusters, we must constrain the star formation histories within their member galaxies and the timescale of virial collapse. In this paper we characterize the complex star-forming properties of a z = 2.5 protocluster in the COSMOS field using ALMA dust continuum and new Very Large Array CO (1–0) observations of two filaments associated with the structure, sometimes referred to as the “Hyperion” protocluster. We focus in particular on the protocluster “core,” which has previously been suggested as the highest-redshift bona fide galaxy cluster traced by extended X-ray emission in a stacked Chandra/XMM image. We reanalyze these data and refute these claims, finding that at least 40% 17% of extended X-ray sources of similar luminosity and size at this redshift arise instead from inverse Compton scattering off recently extinguished radio galaxies rather than intracluster medium. Using ancillary COSMOS data, we also constrain the spectral energy distributions of the two filaments’ eight constituent galaxies from the rest-frame UV to radio. We do not find evidence for enhanced star formation efficiency in the core and conclude that the constituent galaxies are already massive (M _⋆ ≈ 10¹¹ M _⊙), with molecular gas reservoirs >10¹⁰ M _⊙ that will be depleted within 200–400 Myr. Finally, we calculate the halo mass of the nested core at z = 2.5 and conclude that it will collapse into a cluster of (2–9) 10¹⁴ M _⊙, comparable to the size of the Coma Cluster at z = 0 and accounting for at least 50% of the total estimated halo mass of the extended “Hyperion” structure.

为了将星系团与其前身原星系团联系起来，我们必须限制其成员星系内的恒星形成历史和病毒坍缩的时间尺度。在本文中，我们描述了z的复杂恒星形成特性= 2.5 COSMOS 场中的原簇，使用 ALMA 尘埃连续体和新的超大阵列 CO (1-0) 观察与结构相关的两条细丝，有时称为“Hyperion”原簇。我们特别关注原星系团“核心”，它以前被认为是最高红移的真正星系团，由叠加的钱德拉/XMM 图像中的扩展 X 射线发射追踪。我们重新分析了这些数据并反驳了这些说法，发现至少 40% 17% 的扩展 X 射线源在这个红移处具有相似的光度和大小，而不是来自最近熄灭的无线电星系的逆康普顿散射，而不是星团内介质。使用辅助 COSMOS 数据，我们还限制了从静止帧 UV 到无线电的两个细丝的八个组成星系的光谱能量分布。M _⋆ ≈ 10 ¹¹ M _⊙ )，分子气藏 > 10 ¹⁰ M _⊙将在 200-400 Myr 内枯竭。最后，我们计算了z = 2.5处嵌套核心的晕质量，并得出结论，它将坍缩成 (2-9) 10 ¹⁴ M _⊙的星团，与z = 0处的彗发星团的大小相当，并解释了至少 50% 的扩展“Hyperion”结构的总估计晕质量。