Twin Peaks: IC 4329A and Arakelian 120

Abstract

New spectrophotometric observations of the Seyfert 1 galaxies IC 4329A and Arakelian 120 are presented. The low-ionization broad emission lines (as evidenced by Hβ) are strikingly similar. The so-called zero peak in the Balmer lines of these objects appears to be both broader than and blueshifted relative to the [O III] λλ4959, 5007 lines. It is apparently not a narrow-line component. We confirm that the Balmer line profiles in IC 4329A are variable in shape, and we demonstrate that the profile variations are very similar to those seen in Akn 120. This similarity has important implications for models of the central engine and line-emitting regions of AGNs: (1) it implies that some kind of ordered and reproducible motion is taking place in the broad-line region (BLR) and (2) it argues against models explaining the central source of AGNs in terms of separate accretors or supernova events. Profile variability and energy balance considerations argue against the hypothesis that the lines are emitted by an accretion disk. Further clues to the nature of these objects and to the structure of the central engine of AGNs are discussed.