Panels showing two different input (i.e., intrinsic) spectra (black lines) and how the IGM attenuation shapes the observed spectra along different LOS at z = 3.0. All spectra are normalized by the respective underlying input spectrum’s total flux. The gray dashed line shows the multiplication of the respective input spectrum with the median transmission curve, , for all emitters and LOS at the given redshift. The colored solid lines show observed spectra for the same emitter but for different LOS. Wavelengths are evaluated in the halo’s rest-frame. Top: input spectrum obtained as analytic solution of a spherical hydrogen distribution with a column density N = 10²⁰ cm⁻² and temperature T = 10⁴ K (Dijkstra et al. 2006). Bottom: with a Gaussian intrinsic spectrum with standard deviation σ = 200 km s⁻¹.