The signature of high velocity gas in the spectra of NGC 4151
  The multiwavelength emission spectrum and associated velocity field of the Seyfert prototype NGC 4151 is modeled. HST data has impressively revealed the existence of a large range of velocities (100 - 1500 \kms) dominating the emitting clouds in the extended emission line region of the galaxy. Following this observational result, a revision of the photoionization modeling approach applied to NGC 4151 is presented. It is concluded that a mixture of radiation dominated clouds and shock dominated clouds are required to explain the multiwavelength line and continuum spectra of the galaxy. 
M. Contini (1), S.M. Viegas (2), M.A. Prieto (3) ((1) School of   Physics and Astronomy, Tel Aviv University, (2) Instituto ...