PI: Felipe Menanteau, University of Illinois, email@example.com
Address: National Center for Supercomputing Applications, 1205 W. Clark St., Urbana, IL 61801, USA
CoI: John P. Hughes, Rutgers University
CoI: Felipe Barrientos, P. Universidad Catolica de Chile
CoI: Leopoldo Infante, P. Universidad Catolica de Chile
Title: Is ``El Gordo'' the fattest cluster in the Universe?
Abstract: We propose to use optical and near-infrared (NIR) imaging to unveil \em all of the most massive clusters in the observable Universe. We start from the all-sky Planck Sunyaev-Zel'dovich (SZ) catalog, which contains 130 high significance (S/N>5) unconfirmed cluster candidates. Since SZ selection favors high mass clusters and the Planck confirmation process favored low redshift systems, the highest significance unconfirmed candidates are, therefore, likely massive clusters (M_500> 5\times 10^14 M_\odot) at relatively high redshift (z>0.5). Our proposed observations, using the SOAR Optical Imager and Spartan IR Camera and MOSAIC and NEWFIRM on Mayall, are designed to confirm the presence of a brightest cluster galaxy and red sequence of accompanying cluster members to z~1.5. This combination of optical and NIR bands ensures detectability of the red sequence across the full expected redshift range of the SZ clusters and will provide photometric redshifts accurate enough to get an initial mass estimate from the Planck SZ signal. The proposed observations represent the first step required to provide a complete all-sky census throughout the observable Universe of the most massive, high redshift clusters (like ``El Gordo'''). Their expected high redshift and high mass make the unconfirmed Planck clusters, arguably, the most important available sample for probing deviations from (Lambda)CDM and defining the high- mass end of the cluster mass function.
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