An extreme starburst in the core of a rich galaxy cluster at z = 1.7

Tracy Webb, Allison Noble, Andrew Degroot, Gillian Wilson, Adam Muzzin, Nina Bonaventura, Mike Cooper, Anna Delahaye, Ryan Foltz, Chris Lidman, Jason Surace, H. K.C. Yee, Scott Chapman, Loretta Dunne, James Geach, Brian Hayden, Hendrik Hildebrandt, Jiasheng Huang, Alexandra Pope, Matthew W.L. SmithSaul Perlmutter, Alex Tudorica

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


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 Ngal (500 kpc) = 30 8 implies a total halo mass, within 500 kpc, of ∼3.8 1.2 1014 Mo, 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 LIR = 6.2 0.9 1012 Lo. 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 Mo 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.

Original languageEnglish (US)
Article number173
JournalAstrophysical Journal
Issue number2
StatePublished - Aug 20 2015
Externally publishedYes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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