Differential brightness temperature maps for different simulations. The thickness of the slice is  ≈ 2 Mpc. The maps in the left column are when  ⟨ x_α ⟩  = 1, the middles when  ⟨ x_α ⟩  = 10 and the right when  ⟨ x_HII ⟩  = 0.5. The black contour separates absorption and emission region. (l) shows no absorption region.