# $\Omega_{r}$ from WMAP results?

To do some Friedmann-Lemaître cosmology calculations, I would like to know an estimation of $\Omega_{r_0}$ ($\Omega$ radiation today). WMAP 7 give estimation of $\Omega_{b}$, $\Omega_{c}$ and $\Omega_{\Lambda}$ but nothing about $\Omega_{r}$ : http://lambda.gsfc.nasa.gov/product/map/dr4/best_params.cfm Where can I find the best value of $\Omega_{r}$ available today ?

Thank you very much.

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## 2 Answers

Have you tried looking at these: http://arxiv.org/find/astro-ph/1/au:+Larson_D/0/1/0/all/0/1 (Seven year analysis of WMAP data)?

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Perfect. I didn't know that $z_{eq}$ was the redshift of matter-radiation equality. After some calculation for a Friedmannian Universe, we can find that $\Omega_{r_0} = \frac{\Omega_{m_0}}{1+z_{eq}} \approx \frac{0.272}{1+3232} \approx 8.413 \times 10^{-5}$ –  Vincent Jul 1 '12 at 14:03
Glad I could help :) –  dingo_d Jul 1 '12 at 19:40

According to Hyperphysics $\Omega_{rel} = 8.24 \times 10^{-5}$. The article references Carroll, Bradley W. and Ostlie, Dale A., An Introduction to Modern Astrophysics. I don't have this book so I can't comment on how authoritative this figure is.

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