Physics Help Forum Redshift at recombination
 Mar 23rd 2009, 09:30 PM #1 Junior Member   Join Date: Mar 2009 Posts: 1 Redshift at recombination We are to assume the recombination happens at redshift $\displaystyle z_{rec}$ when the number density of photons $\displaystyle n_{\gamma}(z_{rec})$ capable of ionizing hydrogen is exactly equal to the number density of baryons $\displaystyle n_{b}(z_{rec})$. Use the measured number density of baryons, the temperature of the CMB and the blackbody radiation to find out at what redshift $\displaystyle z_{rec}$ we have $\displaystyle n_{\gamma}(z_{rec}) = n_{b}(z_{rec}).$ Proposed Solution: Sorry I don't have time to write in detail what I have so far. But basically I come down to $\displaystyle \Omega_{\gamma}E_{bary} \over hf_{mean}\Omega_{bary}$ $\displaystyle = 1$ However this doesnt make use of blackbody radation, or the temperature of the CMB, if I'm supposed to equate $\displaystyle \Omega_{\gamma}$ to Temperature of the CMB, then I'm not sure how to do that step. Thanks