SPT-CLJ2040-4451: An SZ-Selected Galaxy Cluster at z = 1.478 With Significant Ongoing Star Formation
Abstract
SPT-CLJ2040-4451 -- spectroscopically confirmed at z = 1.478 -- is the highest redshift galaxy cluster yet discovered via the Sunyaev-Zel'dovich effect. SPT-CLJ2040-4451 was a candidate galaxy cluster identified in the first 720 deg2 of the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey, and confirmed in follow-up imaging and spectroscopy. From multi-object spectroscopy with Magellan-I/Baade+IMACS we measure spectroscopic redshifts for 15 cluster member galaxies, all of which have strong [O II] 3727 emission. SPT-CLJ2040-4451 has an SZ-measured mass of M500,SZ = 3.2 +/- 0.8 X 1014 MSun/h70, corresponding to M200,SZ = 5.8 +/- 1.4 X 1014 MSun/h70. The velocity dispersion measured entirely from blue star forming members is sigmav = 1500 +/- 520 km/s. The prevalence of star forming cluster members (galaxies with > 1.5 MSun/yr) implies that this massive, high-redshift cluster is experiencing a phase of active star formation, and supports recent results showing a marked increase in star formation occurring in galaxy clusters at z >1.4. We also compute the probability of finding a cluster as rare as this in the SPT-SZ survey to be >99%, indicating that its discovery is not in tension with the concordance Lambda-CDM cosmological model.
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