COSMIC REIONIZATION

HII bubbles from first stars/galaxies · Gunn-Peterson trough · overlap epoch (z≈6)
Epoch of Reionization

z_reion ≈ 6–15
Overlap: z ≈ 5.5–6

x_HII: -
x_HI: -

Gunn-Peterson optical depth:
τ_GP ∝ x_HI × (1+z)^(3/2)
τ_GP ≈ -

Before overlap: quasar
spectra show complete
Ly-α absorption
(Gunn-Peterson trough)

Planck: τ_reion ≈ 0.054
z_mid ≈ 7.7