Citation
Grego, Laura (1999) Galaxy cluster gas fractions from interferometric measurements of the SunyaevZel'dovich effect. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:08252010152734353
Abstract
Interferometric measurements of the SunyaevZel'dovich effect toward 18 highly xray luminous galaxy clusters are presented. The observations were made using centimeterwave receivers specifically constructed for these observations. The data were taken with the receivers mounted on the Owens Valley Radio Observatory and BerkeleyIllinoisMaryland Association millimeter arrays between 1994 and 1998. The interferometric data are used to determine the gas mass fraction in these clusters in a uniform method. The inteferometric data contain sufficient spatial information to derive models for the pressure distribution of the cluster gas. From these models, under the assumption that the gas is isothermal, the cluster gas masses are estimated and the total gravitating masses are inferred. The total gravitating mass measurement requires the additional assumption that the gas is in hydrostatic equilibrium with the cluster potential. The cluster gas temperatures are obtained from xray spectral observations or, in the few cases in which spectra were unavailable, estimated from xray luminositytemperature relations in the literature. Since the experiment best measures the gas fraction within a fixed angular radius, the measured gas fractions are extrapolated to a fiducial radius, using a relation derived from published numerical simulations, to facilitate comparisons. The best estimate of the cluster gas fraction at τ_(500), the radius at which the enclosed mean density is 500 times the critical density, is (0.071^(+0.010)_(0.012))h^(1)_(100) at 68% confidence. Under the assumption that clusters are fair samples of the universe, the mass composition in clusters at the virial radius should reflect the universal mass composition. The intracluster gas is the dominant component of a cluster's baryonic mass, and so the gas mass fraction is a good approximation of the baryon mass fraction. The baryon fraction in clusters, f_B, together with the universal baryon mass density, Ω_B, sets a limit on the universal mass density, in the standard cosmological paradigm: Ω_M = Ω_B/ f_B. The cluster gas fraction measurements presented here set an upper limit to the universal mass density: Ω_Mh_(100) ≤ 0.27^(+0.07)_(0.06), at 68% confidence. We make our best estimate of the universal matter density, including with the gas fraction estimates of the baryonic mass contained in galaxies and the baryonic mass which failed to become bound during the cluster formation process: Ω_M = 0.29^(+0.08)_(0.06) at 68% confidence for h = 0.7.
Item Type:  Thesis (Dissertation (Ph.D.)) 

Subject Keywords:  Physics 
Degree Grantor:  California Institute of Technology 
Division:  Physics, Mathematics and Astronomy 
Major Option:  Physics 
Thesis Availability:  Restricted to Caltech community only 
Research Advisor(s): 

Thesis Committee: 

Defense Date:  6 November 1998 
Record Number:  CaltechTHESIS:08252010152734353 
Persistent URL:  http://resolver.caltech.edu/CaltechTHESIS:08252010152734353 
Default Usage Policy:  No commercial reproduction, distribution, display or performance rights in this work are provided. 
ID Code:  6008 
Collection:  CaltechTHESIS 
Deposited By:  Dan Anguka 
Deposited On:  25 Aug 2010 23:02 
Last Modified:  26 Dec 2012 04:29 
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