Galaxies tend to be strong emitters of Lyman- photons (from the n = 2 to n =

Galaxies tend to be strong emitters of Lyman-α photons (from the n = 2 to n = 1 transition in atomic hydrogen). But the intergalactic medium the very thin gas between the galaxies— tends to absorb Lyman-α photons. What can you infer from these observations about the temperature in these two environments? Explain.