2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/148492We present a unified picture of active galactic nuclei which we construct from a detailed model of line emission in the active source in NGC 4151. In this scheme NGC 4151 can be regarded as a typical active nucleus, special only in its orientation. This alleviates a number of problems with a unified picture based on a dusty molecular torus with a fixed structure (to which NGC 4151 appears as an anomaly)37 pages LaTeX, (accepted for Astronomy and Astrophysics)Astrophysicstext