NOAO >   Observing Info >   Approved Programs >   2014B-0244

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Proposal Information for 2014B-0244


PI: Anja von der Linden, KIPAC, anja@slac.stanford.edu
Address: Stanford University, 452 Lomita Mall, Stanford, CA 94025, USA

CoI: Steven Allen, KIPAC / Stanford University
CoI: Adam Mantz, KICP / U Chicago
CoI: Adam Wright, KIPAC / Stanford University
CoI: Douglas Applegate, U Bonn
CoI: Patrick Kelly, UC Berkeley
CoI: Glenn Morris, KIPAC / Stanford University
CoI: David Rapetti, Dark Cosmology Centre

Title: Weighing the f_\rm gas Giants

Abstract: The most massive clusters of galaxies are expected to provide nearly fair samples of the matter content of the Universe. Since the X-ray- emitting cluster gas is by far the dominant baryonic mass component in clusters, measurements of the gas-to-total mass ratio in dynamically relaxed clusters (f_\rm gas) provide an excellent estimate of \Omega_\rm b/\Omega_\rm m. Employing standard priors on \Omega_\rm b and H_0, these data yield some of the most robust constraints on \Omega_\rm m, largely independent of the assumed cosmological model. The currently largest systematic uncertainty on \Omega_\rm m stems from uncertainties in total cluster mass estimates, jointly due to temperature calibration uncertainties of X-ray telescopes and the uncertain level of non-thermal pressure support in clusters. By comparing X-ray-derived mass estimates with high-quality weak-lensing mass estimates for a subset of f_\rm gas clusters, we can address this uncertainty directly. Currently, the uncertainty on the weak-lensing mass estimates of relaxed clusters are at the 10% level. We here request a modest amount of time to take additional weak lensing observations for a complete subsample of relaxed clusters, which will allow us to cut this uncertainty in half. These observations will enable a 5% precision measurement of \Omega_\rm m - a remarkable prospect for the determination of one of the key cosmological parameters from a single experiment.


National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360



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