SPT-CL J2040–4451: An SZ-selected Galaxy Cluster at z = 1.478 with Significant Ongoing Star Formation

Creators: Bayliss, M. B.; Lueker, M.; Padin, S.; Shirokoff, E.; Vieira, J. D.

Abstract

SPT-CL J2040–4451—spectroscopically confirmed at z = 1.478—is the highest-redshift galaxy cluster yet discovered via the Sunyaev-Zel'dovich effect. SPT-CL J2040–4451 was a candidate galaxy cluster identified in the first 720 deg^2 of the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey, and has been 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] λλ3727 emission. SPT-CL J2040–4451 has an SZ-measured mass of M_(500, SZ) = 3.2 ± 0.8 × 10^(14) M_☉ h^(-1)_(70), corresponding to M_(200, SZ) = 5.8 ± 1.4 × 10^(14) M_☉ h^(-1)_(70). The velocity dispersion measured entirely from blue star-forming members is σ_v = 1500 ± 520 km s^(–1). The prevalence of star-forming cluster members (galaxies with >1.5 M_☉ yr^(–1)) 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 ΛCDM cosmological model.

Additional Information

© 2014 The American Astronomical Society. Received 2013 July 9; accepted 2014 August 6; published 2014 September 18. The South Pole Telescope program is supported by the National Science Foundation through grant ANT-0638937. Partial support is also provided by the NSF Physics Frontier Center grant PHY-0114422 to the Kavli Institute of Cosmological Physics at the University of Chicago, the Kavli Foundation, and the Gordon and Betty Moore Foundation. Galaxy cluster research at Harvard is supported by NSF grant AST-1009012. Galaxy cluster research at SAO is supported in part by NSF grants AST-1009649 and MRI-0723073. The McGill group acknowledges funding from the National Sciences and Engineering Research Council of Canada, Canada Research Chairs program, and the Canadian Institute for Advanced Research. X-ray research at the CfA is supported through NASA Contract NAS 8-03060. The Munich group acknowledges support from the Excellence Cluster Universe and the DFG research program TR33. This work is based in part on observations obtained with the Spitzer Space Telescope (PID 60099), which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. Additional data were obtained with the 6.5 m Magellan Telescopes located at the Las Campanas Observatory, Chile and the Blanco 4 m Telescope at Cerro Tololo Interamerican Observatories in Chile. R.J.F. is supported by a Clay Fellowship. B.A.B is supported by a KICP Fellowship, M. Bautz acknowledges support from contract 2834-MIT-SAO-4018 from the Pennsylvania State University to the Massachusetts Institute of Technology. M.D. acknowledges support from an Alfred P. Sloan Research Fellowship, W.F. and C.J. acknowledge support from the Smithsonian Institution. This research used resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy under contract No. DE-AC02-05CH11231. The authors also thank the referee, B. Lemaux, for his comments that improved the quality of this paper.

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