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Published August 1, 2015 | Submitted + Published
Journal Article Open

A Massive, Distant Proto-Cluster at z = 2.47 Caught in a Phase of Rapid Formation


Numerical simulations of cosmological structure formation show that the universe's most massive clusters, and the galaxies living in those clusters, assemble rapidly at early times (2.5 < z < 4). While more than 20 proto-clusters have been observed at z ≳ 2 based on associations of 5–40 galaxies around rare sources, the observational evidence for rapid cluster formation is weak. Here we report observations of an asymmetric filamentary structure at z = 2.47 containing 7 starbursting, submillimeter-luminous galaxies and 5 additional active galactic nuclei (AGNs) within a comoving volume of 15,000 Mpc3. As the expected lifetime of both the luminous AGN and starburst phase of a galaxy is ~100 Myr, we conclude that these sources were likely triggered in rapid succession by environmental factors or, alternatively, the duration of these cosmologically rare phenomena is much longer than prior direct measurements suggest. The stellar mass already built up in the structure is ~10^(12) M⊙ and we estimate that the cluster mass will exceed that of the Coma supercluster at z ~ 0. The filamentary structure is in line with hierarchical growth simulations that predict that the peak of cluster activity occurs rapidly at z > 2.

Additional Information

© 2015 The American Astronomical Society. Received 2015 May 8; accepted 2015 June 4; published 2015 July 24. We thank the anonymous referee for constructive comments which have improved the manuscript. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration and made possible by financial support of the W. M. Keck Foundation. We also thank the Joint Astornomy Centre (run by STFC, NSERC, and NOSR) for operation of the JCMT and SCUBA-2 instrument. Mahalo nui loa to the kama'aina of Hawai'i for use of the cultural site of Maunakea for astronomical observing. Based in part on NASA/ESA HST data, operated by STScI of AURA Inc, under NASA contract NAS 5-26555. Other observations obtained from the European Southern Observatory, Chile. C.M.C. acknowledges generous support of a McCue Fellowship from the UC Irvine Center for Cosmology. A.C. and C.M.C. acknowledge support from NSF AST-1313319, NSF CAREER 0645427, and NASA Herschel Science Center.

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Published - 2041-8205_808_2_L33.pdf

Submitted - 1506.01715v2.pdf


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