Effect of Radiative Feedbacks for Resonant Transitions during Cosmological Recombination

Understand

The inhibition of the total HI $n\leftrightarrow 1$ transition rate by delayed resonant reabsorption of HI $(n+1)\to 1$ photons by HI $n\to 1$ line which is possible due to cosmological redshift is considered semi-analytically.

• The method taking into account this effect in the frame of simple three-level approximation model of recombination is suggested.
• It is confirmed that the resonant feedbacks affect ionization fraction at the level about 0.2% for the epoch of last scattering.
• Similar consideration of HeI $2^1P\leftrightarrow 1^1S$ $\Rightarrow$ HeI $2^3P\leftrightarrow 1^1S$ feedback for helium is provided.