OH lines observed in Zw 049.057 with PACS. The black histograms are the observed, continuum-normalized, spectra. Model results from Sect. 3 are also included. The blue curve denotes the model for C_core, which was first constrained using the high-lying H₂O lines detected with PACS, but with an added OH column that was varied in order to also fit the high-lying OH lines. The light-blue curve denotes the model for C_outer, which was first constrained using the H₂O lines detected with SPIRE, but with an added OH column that was varied in order to also account for the residual flux in the low-lying OH lines. The red curve denotes the sum of these two models.