A Massive Protocluster Anchored by a Luminous Quasar at z = 6.63

Feige Wang, Jinyi Yang, Joseph F. Hennawi, Xiaohui Fan, Minghao Yue, Eduardo Bañados, Shane Bechtel, Fuyan Bian, Sarah Bosman, Jaclyn B. Champagne, Frederick B. Davies, Roberto Decarli, Emanuele Paolo Farina, Chiara Mazzucchelli, Bram Venemans, Fabian Walter

Research output: Contribution to journalArticlepeer-review


Protoclusters, the progenitors of galaxy clusters, trace large scale structures in the early Universe and are important to our understanding of structure formation and galaxy evolution. To date, only a handful of protoclusters have been identified in the Epoch of Reionization. As one of the rarest populations in the early Universe, distant quasars that host active supermassive black holes are thought to reside in the most massive dark matter halos at that cosmic epoch and could thus potentially pinpoint some of the earliest protoclusters. In this Letter, we report the discovery of a massive protocluster around a luminous quasar at z = 6.63. This protocluster is anchored by the quasar and includes three [C ii] emitters at z ∼ 6.63, 12 spectroscopically confirmed Lyα emitters (LAEs) at 6.54 < z ≤ 6.64, and a large number of narrow-band-imaging selected LAE candidates at the same redshift. This structure has an overall overdensity of δ = 3.3 − 0.9 + 1.1 within ∼35 × 74 cMpc2 on the sky and an extreme overdensity of δ > 30 in its central region (i.e., R ≲ 2 cMpc). We estimate that this protocluster will collapse into a galaxy cluster with a mass of 6.9 − 1.4 + 1.2 × 10 15 M ⊙ at the current epoch, more massive than the most massive clusters known in the local Universe such as Coma. In the quasar vicinity, we discover a double-peaked LAE, which implies that the quasar has a UV lifetime greater than 0.8 Myrs and has already ionized its surrounding intergalactic medium.

Original languageEnglish (US)
Article numberL11
JournalAstrophysical Journal Letters
Issue number1
StatePublished - Feb 1 2024

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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