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An X-ray-Emitting Proto-Cluster at $z\approx5.7$ Reveals Rapid Structure Growth

Cosmology and Nongalactic Astrophysics 2026-01-29 v1 Astrophysics of Galaxies High Energy Astrophysical Phenomena

Abstract

Galaxy clusters are the most massive gravitationally bound structures in the universe and serve as tracers of the assembly of large-scale structure. Studying their progenitors, proto-clusters, sheds light on the earliest stages of cluster formation. Yet, detecting proto-clusters is demanding: their member galaxies are loosely bound and the emerging hot intracluster medium (ICM) may only be in the initial stages of virialization. Recent JWST observations located several proto-cluster candidates by identifying overdensities of z5z\gtrsim5 galaxies. However, none of these candidates was detected by X-ray observations, which offer a powerful way to unveil the hot ICM. Here, we report the combined Chandra and JWST detection of a proto-cluster, JADES-ID1, at z5.68z\approx5.68, merely one billion years after the Big Bang. We measure a bolometric X-ray luminosity of Lbol=(1.50.6+0.5)×1044 erg s1L_{\rm bol} = (1.5^{+0.5}_{-0.6}) \times10^{44} \ \rm{erg \ s^{-1}} and infer a total gravitating mass of M500=(1.80.7+0.6)×1013 MM_{500}= (1.8^{+0.6}_{-0.7}) \times 10^{13} \ \rm{M_{\odot}}, making this system a progenitor of today's most massive galaxy clusters. The detection of extended, shock-heated gas indicates that substantial ICM heating can occur in massive halos as early as z5.7z\approx5.7. In addition, given the limited survey volume, the discovery of such a massive cluster is statistically unlikely, implying that the formation of the large-scale structure must have occurred more rapidly in some regions of the early universe than standard cosmological models predict.

Keywords

Cite

@article{arxiv.2601.19978,
  title  = {An X-ray-Emitting Proto-Cluster at $z\approx5.7$ Reveals Rapid Structure Growth},
  author = {Akos Bogdan and Gerrit Schellenberger and Qiong Li and Christopher J. Conselice},
  journal= {arXiv preprint arXiv:2601.19978},
  year   = {2026}
}

Comments

Accepted for publication in Nature