While brief - well in reducing the problem to approximate...

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While brief, the epoch of recombination did have a nonzero duration, which translates into a finite thickness in redshift. As set out by Jones and Wyse (1985 A&A 149, 144), the cosmological dependences cancel almost perfectly giving an optical-depth function τ( z ) = 0.37 ( z /1000) 14.25 . Thus the distribution of last-scattering redshift (specifically e dτ/dz ) is strongly peaked, almost Gaussian with mean of z =1065 and standard deviation σ z = 80. (WMAP data give z rec = 1089 ± 97). This will modify the spectrum slightly with respect to a perfect single- temperature blackbody, and will be manifested by damping out irregularities due to structure which is smaller than the comoving depth of this apparent shell. Details of the recombination process have been recently re-examined by Seager, Sasselov, and Scott (2000, ApJS 128, 431) using full radiative transfer codes and sophisticated models for all the relevant ions, who found that Peebles (1968 ApJ 153, 1) and Zel'dovich et al. (1968 JETP Lett. 28, 146) did remarkably
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Unformatted text preview: well in reducing the problem to approximate differental equations. Further details exist, but at about the level of uncertainty in some of the relevant reaction rates. In evaluating the spectrum of the background radiation, it is noteworthy (see the treatment by Peacock, for example) that the thermal form of the radiation spectrum was established when brehmsstrahlung was active at redshift of order 10 6 and no major additional input between then and recombination is allowed by the existing limits on departures from a Planck form. Further developments should come fast, with NASA's Wilkinson Microwave Anisotropy Probe (WMAP) still operating in the L2 region and and ESA's Planck in the pipeline. These should yield significant measurements of high-order harmonics in the fluctuation spectrum sufficient to measure the basic cosmological parameters by themselves....
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This note was uploaded on 11/10/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.

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