Polarimetric view of the changing type Seyfert galaxy ESO 362-G018.

Abstract

ESO362-G018 is an active galactic nucleus (AGN) which is classified as a Seyfert 1.5 galaxy e.g. by Bennert et al. (2006), (black data set on figure 1). However, Parisi et. al (2009) found an optical spectrum of this source which was taken during the 6dF Galaxy Survey, but it does not show the broad Balmer lines required to classify it as Seyfert 1 galaxy (red data set on figure 1). On the other hand, the results obtained by Agis-Gonzalez et al. (2014❩ in a X-ray analysis of this same source reveal that the inclination of ESO362- G018 i = 53° ± 5° is consistent with the picture of an AGN looked through the upper layers of a clumpy, dusty torus. Thus, according to the Unification Models of AGN and the clumpy nature of the torus, our interpretation of the different spectra is the following one. On 30th of January of 2003 (when the spectrum belonging to the 6dF survey was obtained), our line of sight intercepted a (or several aligned) torus clump(s) with much greater column density than its environment. Accordingly, the nucleus and the broad line region (❨BLR)❩ would be obscured. This allowed only the narrow emission lines to emerge from the narrow line region (NRL). Otherwise, on 18th of September of 2004 (when the spectrum by Bennert et al. 2006 was obtained) there is no clump to intercept and the BLR is not obscured so that the broad Balmer emission lines could be detected.