Differences between the two types Seyfert 2 galaxies – With and without polarized broad lines

Based on spectropolarimetric observations Seyfert 2 (Sy2) galaxies are generally divided into two populations. Some Sy2s show polarized broad emission lines (PBLs) which is an evidence for the hypothesis of the Unified model while others do not. In order to determine the properties of these two apparently different populations we compiled a sample of 66 Sy2 objects with and without detected PBLs. We used a (J − H) − (H − Ks) diagram based on 2MASS J, H, Ks magnitudes in 14 arcsec aperture, the F[OIII] emission line flux and the infrared emission flux FKsFKs using the Ks filter. From the (J − H) − (H − Ks) diagram we determined that one third of the Sy2 objects with PBLs have a power-law infrared component which could be a result of both a non-thermal AGN component scattered by free electrons (or dust) and emission from hot dust near its sublimation temperature. The rest of the objects (with PBLs) are significantly dominated by a dust thermal re-emission. The Sy2s without PBLs show infrared emission dominated by a host galaxy stellar component and also by thermal dust re-emission. The Sy2s with PBLs tend to have a few times larger L[OIII] luminosities than those without. Following the median values of F[OIII]/FKsF[OIII]/FKs, it seems that this ratio is sensitive enough to separate our sample of Sy2 galaxies into two types – with and without PBLs. There are no Sy2s with PBLs having Eddington ratio below 10−3 which confirms the results of Nicastro et al. (2003).

► We compiled a sample of 66 Sy2 objects with and without detected PBLs. ► One third of the Sy2 galaxies with PBLs show a power-law infrared component. ► The Sy2s without PBLs show infrared emission dominated by thermal dust re-emission. ► F_[OIII]/F_Ks ratio is sensitive enough to separate our sample Sy2s into two types. ► There are no Sy2s with PBLs having Eddington ratio below 10−3.