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					Using Lyman beta Gunn-Peterson
           Trough

           Xiaohui Fan
            Jan, 2004
• Total Observed Transmitted Flux:

• It is related to optical depth as:




  due the non-uniformity of IGM, one has to include
  the density distribution function, typically from
  simulation
• In case of Ly beta transition:

• One has to consider foreground Ly alpha as well:
• Because of the non-uniform density distribution of
  the IGM, Ly beta is not exactly 5.27 times more
  efficient than Ly alpha. It turns out to be actually
  about 3 times more efficient. I.e., the same optical
  depth one puts on Ly beta (after correct for the
  foreground) corresponds to about three times
  higher neutral hydrogen fraction.
    Strong Evolution of
Gunn-Peterson Optical Depth




                     Transition at z~6?




           Fan et al. 2004
Without correcting foreground
Ly beta alone:
    Converting Beta to Alpha
(factor of three, instead of 5.27)




                        Transition at z~6?




              Fan et al. 2004

				
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