Are There Larger Stellar Velocity Dispersions in Low-redshift Type 1 AGNs than in Type 2 AGNs?

The main objective of this article is to check the Unified Model (UM) for the expected similar stellar velocity dispersions between Type 1 and Type 2 active galactic nuclei (AGNs) and then to provide further clues on black hole (BH) mass properties. Unlike previous comparisons of BH masses estimated from M (BH)-sigma relations for Type 2 AGNs and from virial BH masses for Type 1 AGNs, reliable stellar velocity dispersions sigma measured from absorption features around 4000 angstrom are directly compared between the thus far largest samples of 6260 low-redshift (z < 0.3) Type 1 AGNs and almost all Type 2 AGNs in SDSS DR12. Although half of Type 1 AGNs do not have a measured sigma due to unapparent absorption features overwhelmed by AGN activities, both properties of the mean spectra of Type 1 AGNs with and without a measured sigma and a positive dependence of sigma on the [O iii] luminosity can lead to a statistically larger sigma for all Type 1 AGNs compared to the 6260 Type 1 AGNs with measured stellar velocity dispersions. Then, direct sigma comparisons can lead to a statistically larger sigma in Type 1 AGNs, with a confidence level higher than 10 sigma, after considering the necessary effects of different redshifts and different central AGN activities. Although Type 1 AGNs have a sigma of only about (9 +/- 3)% larger than Type 2 AGNs, the difference cannot be well explained at the current stage. Unless there is strong evidence to support different M (BH)-sigma relations or to support quite different evolutionary histories between Type 1 and Type 2 AGNs, the statistically larger sigma in Type 1 AGNs provides a strong challenge to the UM of AGNs.