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

In the manuscript, we check properties of electron densities n e traced by flux ratio R sii of [S ii ] λ 6716 Å to [S ii ] λ 6731 Å in narrow emission line regions (NLRs) between Type-1 active galactic nucleus (AGN) and Type-2 AGN in SDSS Data Release 12 (DR12). Under the framework of unified model...

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Bibliographic Details
Published in:The Astrophysical journal 2024-01, Vol.960 (2), p.108
Main Author: Zhang, XueGuang
Format: Article
Language:English
Subjects:
Active galactic nuclei
Active galaxies
Astrophysics
Confidence intervals
Electron density
Electron temperatures
Electrons
Emission
Emission line galaxies
Emission lines
Galaxies
H II regions
Linings
Seyfert galaxies
Star formation
Temperature effects
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Summary:In the manuscript, we check properties of electron densities n e traced by flux ratio R sii of [S ii ] λ 6716 Å to [S ii ] λ 6731 Å in narrow emission line regions (NLRs) between Type-1 active galactic nucleus (AGN) and Type-2 AGN in SDSS Data Release 12 (DR12). Under the framework of unified model considering kiloparsec-scale structures, similar n e in NLRs should be expected between Type-1 AGN and Type-2 AGN. Based on reliable measurements of the [S ii ] doublet with measured parameters at least 5 times larger than corresponding uncertainties, there are 6039 Type-1 AGN and 8725 Type-2 AGN (excluding the Type-2 LINERs and the composite galaxies) collected from SDSS DR12. Then, lower R sii (higher n e ) in NLRs can be well confirmed in Type-1 AGN than in Type-2 AGN, with the confidence level higher than 5 σ , even after considering the necessary effects including effects of electron temperatures traced by [O iii ] λ 4364,4959,5007 Å on estimating n e in NLRs. Two probable methods are proposed to explain the higher n e in NLRs in Type-1 AGN. First, the higher n e in NLRs of Type-1 AGN could indicate longer time durations of AGN activities in Type-1 AGN than in Type-2 AGN, if AGN activities triggering galactic-scale outflows leading to more electrons injecting into NLRs were accepted to explain the higher n e in NLRs of Type-2 AGN than H ii galaxies. Second, the lower n e in NLRs of Type-2 AGN could be explained by stronger star-forming contributions in Type-2 AGN, considering lower n e in H ii regions. The results provide interesting challenges to the commonly and widely accepted unified model of AGN.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ad029a