Journal
ASTROPHYSICAL JOURNAL
Volume 922, Issue 2, Pages -Publisher
IOP Publishing Ltd
DOI: 10.3847/1538-4357/ac1e8d
Keywords
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Categories
Funding
- Indiana Space grant Consortium
- NASA [NNX12AE06G, 80NSSc20K0440]
- Alfred P. Sloan Foundation
- U.S. Department of Energy Office of Science
- University of Arizona
- Brazilian Participation Group
- Brookhaven National Laboratory
- Carnegie Mellon University
- French Participation Group
- German Participation Group
- Harvard University
- Instituto de Astrofisica de Canarias
- Michigan State/Notre Dame/JINA Participation Group
- Johns Hopkins University
- Lawrence Berkeley National Laboratory
- Max Planck Institute for Astrophysics
- Max Planck Institute for Extraterrestrial Physics
- Pennsylvania State University
- Princeton University
- Spanish Participation Group
- Yale University
- University of Florida
- University of Utah
- Vanderbilt University
- University of Virginia
- University of Washington
- New Mexico State University
- New York University
- University of Portsmouth
- University of Tokyo
- NASA [53386, NNX12AE06G] Funding Source: Federal RePORTER
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The study found that mixing is not the principal cause of the extended morphology of the observed branch, but rather Seyferts/LINERs intrinsically have a wide range of line ratios. Variations in ionization parameter and metallicity can explain much of the diversity of Seyfert/LINER line ratios.
Ionization sources other than H ii regions give rise to the right-hand branch in the standard ([N ii]) BPT diagram, populated by Seyfert 2s and LINERs. However, because the majority of Seyfert/LINER hosts are star-forming (SF), H ii regions contaminate the observed lines to some extent, making it unclear if the position along the branch is merely due to various degrees of mixing between pure Seyferts/LINERs and SF, or whether it reflects the intrinsic diversity of Seyfert/LINER ionizing sources. In this study, we empirically remove SF contributions in similar to 100,000 Seyferts/LINERs from SDSS using the doppelganger method. We find that mixing is not the principal cause of the extended morphology of the observed branch. Rather, Seyferts/LINERs intrinsically have a wide range of line ratios. Variations in ionization parameter and metallicity can account for much of the diversity of Seyfert/LINER line ratios, but the hardness of the ionization field also varies significantly. Furthermore, our k-means classification on seven decontaminated emission lines reveals that LINERs are made up of two populations, which we call soft and hard LINERs. The Seyfert 2s differ from both types of LINERs primarily by higher ionization parameter, whereas the two LINER types mainly differ from each other (and from star-forming regions) in the hardness of the radiation field. We confirm that the [N ii] BPT diagram more efficiently identifies LINERs than [S ii] and [O i] diagnostics, because in the latter many LINERs, especially soft ones, occupy the same location as pure starformers, even after the SF has been removed from LINER emission.
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