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Cosmological Parameters from WMAP and SDSS

February 22, 2005. WMAP

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Cosmological Parameters from WMAP and SDSS

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    1. February 22, 2005 WMAP & SDSS Cosmology 1 Cosmological Parameters from WMAP and SDSS Greg Thompson Astronomy Bag Lunch February 22, 2005

    2. February 22, 2005 WMAP & SDSS Cosmology 2 Outline In the beginning … The Cosmological Parameters The CMB and Temperature Fluctuations The WMAP Results Large Scale Structure (LSS) The SDSS Power Spectrum Combining the WMAP and SDSS results

    3. February 22, 2005 WMAP & SDSS Cosmology 3 In the beginning… There was something … and then something happened and our universe was “born”. This birth happened in an explosion of space called the “big bang.” The very early universe was in an ultra-hot and dense state and radiated as a blackbody. As the universe expanded, it cooled and the once very hot blackbody radiation was redshifted into the microwave regime at T ~ 2.7 K. While in its hot, dense state the universe consisted of photons and baryons coupled together in a photon-baryon fluid. At z = 3600 or tmr = 50,000 yrs the radiation and matter densities were equal. Prior to that time, the universe was radiation dominated. After that time, the universe became matter dominated. At z = 1400 or trec = 250,000 yrs electrons combined with baryons to form neutral matter for the first time.

    4. February 22, 2005 WMAP & SDSS Cosmology 4 At z = 1100 or tdec = 350,000 yrs the photons are decoupled from the matter and are free to travel to us to be observed. These will be the CMB photons. The sphere from which we observe these photons is called the last scattering surface. Any inhomogeneities in the universe at the time of last scattering will leave their imprint in the CMB. What are the cosmological parameters? a(t) - the scale factor - a dimensionless function that describes how distances in a homogeneous, isotropic universe expand or contract with time. Normalized so that at the current time, t0, a(t0) = 1. H(t) - the Hubble parameter - characterizes the rate of expansion and has units of km s-1 Mpc-1. Defined as:

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