HST-COS view of the I Zw 1 absorption-affected N V emission feature. The continuum level is depicted as a grey dotted line, the emission line profile as a red dashed line and the total modelled emission is shown as a solid red line. The positions of N V absorption features (A, B, C, and D) are labelled, as well as the identified ISM lines. The strong P II+O I blend overlaps the blue component of the most blue-shifted N V absorption system.