The structure of the Akn 120 emitting region: The line shapes and long-term Hβ line profile variation

Abstract

To investigate the structure of the Akn 120 emitting region we have analysed the spectral line profiles of H_alpha, H_beta, Ly_alpha, C III[1909], C IV[1549] and Mg II[2798] lines using a Gaussian-decomposition approach. The decomposed shape of the Akn 120 lines indicates three separated broad line-emitting regions, in two of them, the systematic motions of emitting gas are present. It seems that one of the two regions has a high random velocity of emitters (~2500 km s^-1) and approaching line-of-sight velocities, and the other has a smaller random velocity of emitters (~1000 km s^-1) and receding line-of-sight velocities. Also, we discuss the long-term H_beta line shape variation in the spectra of Akn 120. The H_beta line (from 96 spectra) was fitted with three broad and one narrow Gaussians through the entire period considered (1977-1990). The central broad as well as blue component of H_beta and shelf (Fe II template) cause the H_beta line shape variation. Besides the Gaussian decomposition of the shapes of the three hydrogen lines we propose here a disk model with two more regions located symmetrically to the disk plane. Using the fitting method with the disk model we obtained the parameters of the disk: i=10^o; R_inn~ 120-200 R_g, R_out~ 1000 R_g.