Line-of-sight integrated flux for each carbon cycle species for the ζ(N) model and deviations in the integrated flux from models using different ζ_c. First column: velocity-integrated emission of the [CII] 158 μm (top), [CI] 609 μm (middle), and CO (1–0) (bottom) emission in units of (K km s⁻¹). Second to fourth columns: relative emission for the different constant CR ionization rate models with respect to the ζ(N) model.