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

Abstract

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–σ relations for Type 2 AGNs and from virial BH masses for Type 1 AGNs, reliable stellar velocity dispersions σ measured from absorption features around 4000 Å 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 σ due to unapparent absorption features overwhelmed by AGN activities, both properties of the mean spectra of Type 1 AGNs with and without a measured σ and a positive dependence of σ on the [O iii] luminosity can lead to a statistically larger σ for all Type 1 AGNs compared to the 6260 Type 1 AGNs with measured stellar velocity dispersions. Then, direct σ comparisons can lead to a statistically larger σ in Type 1 AGNs, with a confidence level higher than 10σ, after considering the necessary effects of different redshifts and different central AGN activities. Although Type 1 AGNs have a σ 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–σ relations or to support quite different evolutionary histories between Type 1 and Type 2 AGNs, the statistically larger σ in Type 1 AGNs provides a strong challenge to the UM of AGNs.

Are There Higher Electron Densities in Narrow Emission Line Regions of Type-1 AGNs than in Type-2 AGNs?

“…Bornancini & Garcia Lambas (2020) have shown significantly different properties of UV and/or optical and mid-infrared color distribution of the different AGN types. More recently, we, Zhang (2022b), have shown statistically larger stellar velocity dispersion in Type-1 AGN than in Type-2 AGN. As the detailed discussions on the UM in Netzer (2015), the UM has been successfully applied to explain different observed features between Type-1 and Type-2 AGN in many different ways; however, the AGN family with many other features considering the reported challenges to the UM are far from homogeneous.…”

“…The common simple stellar population (SSP) method (Bruzual & Charlot 2003;Kauffmann et al 2003;Cid Fernandes et al 2005;Cappellari 2017) has been applied to determine the host galaxy contributions, similar as what we have done in Zhang (2014Zhang ( , 2021aZhang ( , 2021bZhang ( , 2021cZhang ( , 2022bZhang ( , 2023, Zhang & Feng (2016), Rakshit et al (2017), andZhang et al (2019). We have exploited the 39 simple stellar population templates in Bruzual & Charlot (2003), which can be used to well describe the characteristics of almost all the SDSS galaxies as discussed in Bruzual & Charlot (2003).…”

Estimating sizes of type-2 AGN narrow-line regions from multiple survey spectra – a demonstration

“…Bornancini et al (2020) have shown significantly different properties of UV/optical and mid-infrared colour distribution of the different AGN types. More recently, we Zhang (2022b) have shown statistically larger stellar velocity dispersion in Type-1 AGN than in Type-2 AGN. As the detailed discussions on the UM in Netzer (2015), the UM has been successfully applied to explain different observed features between Type-1 and Type-2 AGN in many different ways, however, the AGN family with many other features considering the reported challenges to the UM are far from homogeneous.…”

Systematic Research of Low-redshift Optically Selected SDSS Type 2 AGNs but with Apparent Long-term Optical Variabilities from Catalina Sky Survey. I. Data Sample and Basic Results

“…More recently, different host-galaxy properties have been discussed in Bornancini & Garcia Lambas (2020), to favor an evolutionary scenario rather than a strict UM in obscured and unobscured AGNs. Probably higher stellar velocity dispersions have been reported in our recent paper (Zhang 2022a). As detailed in discussions in Netzer (2015), the UM has been successfully applied to explain different features between Type 1 and Type 2 AGNs in many different ways; however, there are many other features of structures and/or environments proved to be far from homogeneous among the AGN family.…”

“…More detailed descriptions on the SSP method can be found in Bruzual & Charlot (2003), Kauffmann et al (2003b), Cid Fernandes et al (2005, and Cappellari (2017). And the SSP method has been applied in our previous papers (Zhang 2014(Zhang , 2021a(Zhang , 2021c(Zhang , 2021d(Zhang , 2022aZhang & Feng 2016;Rakshit et al 2017;Zhang et al 2019). Here, we do not show further discussions on the SSP method anymore, but simple descriptions on SSP method are described as follows.…”