Matter temperature during cosmological recombination

Abstract

The temperature of the atomic matter in the Universe is held to that of the cosmic background radiation until decoupling at z ∼ 100. After this, it cools faster than the radiation [∝ (1 + z)2 rather than (1 + z)] and would have fallen to about 20 mK today if astrophysical feedback processes had not heated up the interglactic medium. We show how the derivative of the Compton coupling equation helps numerically to follow the decoupling process. © 2009 RAS.