The Wouthuysen Field Absorption Trough in Cosmic Strings Wakes

The baryon density enhancement in cosmic string wakes leads to a stronger coupling of the spin temperature to the gas kinetic temperate inside these string wakes than in the intergalactic medium (IGM). The Wouthuysen Field (WF) effect has the potential to enhance this coupling to such an extent that it may result in the strongest and cleanest cosmic string signature in the currently planned radio telescope projects. Here we consider this enhancement under the assumption that X-ray heating is not significant. We show that the size of this effect in a cosmic string wake leads to a brightness temperature at least two times more negative than in the surrounding IGM. If the SCI-HI [1, 2] or EDGES [3, 4] experiment confirm a WF absorption trough in the cosmic gas, then cosmic string wakes should appear clearly in 21 cm redshift surveys of z = 10 to 30.