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 , ( SpARCS ) , and confirmed through Keck-MOSFIRE spectroscopy .
The rest-frame optical richness of N _ { \mathrm { gal } } ( 500kpc ) = 30 \pm 8 implies a total halo mass , within 500kpc , of \sim 3.8 \pm 1.2 \times 10 ^ { 14 } M _ { \odot } , 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 ( HST ) .
The mid/far-infrared ( M/FIR ) data detect an Ultra-luminous Infrared Galaxy spatially coincident with the central galaxy , with L _ { \mathrm { IR } } = 6.2 \pm 0.9 \times 10 ^ { 12 } L _ { \odot } .
The detection of polycyclic aromatic hydrocarbons ( PAHs ) 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 \sim 860 \pm 130 M _ { \odot } yr ^ { -1 } .
The optical source corresponding to the IR emission is likely a chain of 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 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 .