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

Abstract

Abstract.To investigate the structure of the Akn 120 emitting region we have analysed the spectral line profiles of Hα, H β , Lyα, 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 β line shape variation in the spectra of Akn 120. The H β line (from 96 spectra) was fitted with three broad and one narrow Gaussians through the entire period considered (1977)(1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990). The central broad as well as blue component of H β and shelf (Fe II template) cause the H β 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• ; Rinn ≈ 120−200 Rg, Rout ≈ 1000 Rg.Key words. galaxies: individual (Arakelian 120) -galaxies: Seyfert -line: profiles -accretion, accretion disks IntroductionThe spectral line investigation of Active Galactic Nuclei (AGNs) helps us to understand physical properties and kinematics of emitting gas. The AGN radiation comes from a compact very luminous center of a galaxy, and in their spectra narrow and broad emission lines are observed. These lines come from a very extensive emitting line region, where plasma has very different parameters; the electron density can range from 10 2 cm −3 to 10 11 cm −3and electron temperatures from several hundreds to tens of thousands Kelvin (see e.g. Osterbrock 1990). It is widely accepted that the "central engine" consists of a massive black hole fueled by an accretion disk. Also, observations in a wide band of wavelengths (X, UV, optical) indicate that an accretion disk should be present as a central part of the majority of AGNs. Emission line profiles of Active Galactic Nuclei usually show variabilities. Investigations of these variations could provide information about the structure, size and kinematics of the emitting gas in the central part of these objects (see e.g. Foltz et al. 1983;Peterson et al. 1985Peterson et al. , 1989Peterson et al. , 1998Peterson & Gaskell 1991; Peterson 1993;Winge et al. Send offprint requests to: L.Č. Popović, e-mail: lpopovic@aob.bg.ac.yu 1996; Wandel et al. 1999, etc.). According to the standard model, the broad emission lines observed in spectra of AGNs originate in the high-velocity gas of the surrounding Broad Line Region (BLR) ionized by the UV and optical radiation of the compact central source. Fluctuation in the ionizing continuum cause the variations in emissio...

Balmer lines emission region in NGC 3516: Kinematical and physical properties

“…To limit the number of free parameters in the fit of the Hβ line we have also set some a priori restrictions on the narrow components and satellite lines (Popović & Mediavilla 1997;Popović et al 2001Popović et al , 2002. In the first place, the three narrow Gaussians representing the two [OIII]λλ4959, 5007 lines and the narrow Hβ component are preconditioned to have the same redshift and full widths proportional to their wavelengths.…”

“…Finally, we have included in the fit a shelf of Fe II template (Korista 1992;Popović et al 2001Popović et al , 2002.…”

“…One possibility is that the central dip of the line associated to the disk geometry may be masked by broad emission coming from elsewhere. A two component model including an accretion disk and a region with different geometry covering the disk has satisfactorily described the emission lines of Akn 120 (Popović et al 2001) and III Zw 2 (Popović et al 2002).…”

“…van Groningen 1987;Sulentic et al 1998;Sulentic 1999;Popović et al 2001Popović et al , 2002. One possibility is that the central dip of the line associated to the disk geometry may be masked by broad emission coming from elsewhere.…”

Mg II spectral line broadening in helium, oxygen and argon-helium plasmas

“…They are used in astrophysical plasma diagnostics and modeling (Danezis et al 2003;Eracleous & Halpern 2003;Bohm-Vitense et al 2001;Arav et al 2001;Lobel & Dupree 2000;Charlton et al 2000;Wood & Karovska 2000;Luttermoser 2000;Popović et al 2001;Uitenbroek & Briand 1995, and in many other studies). Therefore, knowledge of the Mg II spectral line characteristics (the widths and the shifts) are of interest.…”