NOAO >   Observing Info >   Approved Programs >   2015A-0121

# Program Information for 2015A-0121

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

CoI: Steven Allen, Stanford U.
CoI: Adam Mantz, U. of Chicago
CoI: Douglas Applegate, Universitat Bonn
CoI: Patrick Kelly, UC Berkeley
CoI: Glenn Morrison, Stanford U.
CoI: David Rapetti, Dark Cosmology Center

Title: Weighing the f_ 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 dominant 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 unknown 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 precision on the weak-lensing mass normalization of relaxed clusters is 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.

Program Type: Long Term/Extragalactic

Scheduled Nights:
Run 1 (2015A):  CT-4m/DECam -- 2.5n on Mar 19 - Mar 23 2015
Run 1 (2016A):  CT-4m/DECam -- 1.5n on Mar 08 - Mar 10 2016

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

 NOAO >   Observing Info >   Approved Programs >   2015A-0121