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Published August 20, 2015 | Published
Journal Article Open

An Extreme Starburst in the Core of a Rich Galaxy Cluster at z = 1.7


We have discovered an optically rich galaxy cluster at z = 1.7089 with star formation occurring in close proximity to the central galaxy. The system, SpARCS104922.6+564032.5, was detected within the Spitzer Adaptation of the red-sequence Cluster Survey, and confirmed through Keck-MOSFIRE spectroscopy. The rest-frame optical richness of N_(gal) (500 kpc) = 30 ± 8 implies a total halo mass, within 500 kpc, of ~3.8 ± 1.2 × 10^(14) M⊙, comparable to other clusters at or above this redshift. There is a wealth of ancillary data available, including Canada–France–Hawaii Telescope optical, UKIRT-K, Spitzer-IRAC/MIPS, and Herschel-SPIRE. This work adds submillimeter imaging with the SCUBA2 camera on the James Clerk Maxwell Telescope and near-infrared imaging with the Hubble Space Telescope. The mid/far-infrared (M/FIR) data detect an Ultra-luminous Infrared Galaxy spatially coincident with the central galaxy, with L_(IR) = 6.2 ± 0.9 × 10^(12) L⊙. The detection of polycyclic aromatic hydrocarbons at z = 1.7 in a Spitzer-IRS spectrum of the source implies the FIR luminosity is dominated by star formation (an Active Galactic Nucleus contribution of 20%) with a rate of ~860 ± 130 M⊙ yr^(−1). The optical source corresponding to the IR emission is likely a chain of >10 individual clumps arranged as "beads on a string" over a linear scale of 66 kpc. Its morphology and proximity to the Brightest Cluster Galaxy (BCG) imply a gas-rich interaction at the center of the cluster triggered the star formation. This system indicates that wet mergers may be an important process in forming the stellar mass of BCGs at early times.

Additional Information

© 2015 The American Astronomical Society. Received 2015 February 17; accepted 2015 July 2; published 2015 August 21. 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. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Financial support for this work was provided by NASA through program GO-13677 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. This material is based upon work supported in part by the US Department of Energy, Office of Science, Office of High Energy Physics, under contract No. AC02-05CH11231. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. L.D. acknowledges support from European Research Council Advanced Grant: cosmicism. T.M.A.W. acknowledges the support of an NSERC Discovery Grant. Financial support for this work was provided by NASA through programs GO-13306, GO-13677, GO-13747, GO-13845, and GO-14327 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. Facilities: HST (WFC3) - Hubble Space Telescope satellite, Spitzer - Spitzer Space Telescope satellite, JCMT - James Clerk Maxwell Telescope, Keck:I - , Herschel - European Space Agency's Herschel space observatory, CFHT - Canada-France-Hawaii Telescope, UKIRT - United Kingdom Infrared Telescope.

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August 20, 2023
August 20, 2023