We present X-ray and spectroscopic confirmation of a cluster assembling from multiple, distinct galaxy groups at z = 0.371. Initially detected in the Las Campanas Distant Cluster Survey, the structure contains at least four X-ray-detected groups that lie within a maximum projected separation of 4 Mpc and within Δυ — 550 km s~(-1) of one another. Using Chandra imaging and wide-field optical spectroscopy, we show that the individual groups lie on the local σ-T relation and derive a total mass of M ≥ 5 x 10~(14) solar mass for the entire structure. We demonstrate that the groups are gravitationally bound to one another and will merge into a single cluster with about one-third or more the mass of Coma. We also find that although the cluster is in the process of forming, the individual groups already have a higher fraction of passive members than the field. This result indicates that galaxy evolution on group scales is key to developing the early-type galaxies that dominate the cluster population by z ～ 0.
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机译：我们目前的X射线和光谱确认从z = 0.371的多个不同的星系组组装的群集。该结构最初在Las Campanas遥远星团调查中检测到，包含至少四个X射线检测组，它们位于最大投影间隔为4 Mpc且彼此之间Δυ— 550 km s〜（-1）之内。使用钱德拉成像和广域光谱学，我们表明，各个组位于局部σ-T关系上，并得出整个结构的总质量M≥5 x 10〜（14）太阳质量。我们证明了各组在重力上相互绑定，并且将合并成一个具有约三分之一或更多的昏迷质量的群集。我们还发现，尽管集群处于形成过程中，但各个组已拥有比该领域更高比例的被动成员。这一结果表明，群尺度上的星系演化对于发展以z〜0为主导星团种群的早期类型星系至关重要。
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