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Title: Galaxy emission line classification using three-dimensional line ratio diagrams

Two-dimensional (2D) line ratio diagnostic diagrams have become a key tool in understanding the excitation mechanisms of galaxies. The curves used to separate the different regions—H II-like or excited by an active galactic nucleus (AGN)—have been refined over time but the core technique has not evolved significantly. However, the classification of galaxies based on their emission line ratios really is a multi-dimensional problem. Here we exploit recent software developments to explore the potential of three-dimensional (3D) line ratio diagnostic diagrams. We introduce the ZQE diagrams, which are a specific set of 3D diagrams that separate the oxygen abundance and the ionization parameter of H II region-like spectra and also enable us to probe the excitation mechanism of the gas. By examining these new 3D spaces interactively, we define the ZE diagnostics, a new set of 2D diagnostics that can provide the metallicity of objects excited by hot young stars and that cleanly separate H II region-like objects from the different classes of AGNs. We show that these ZE diagnostics are consistent with the key log [N II]/Hα versus log [O III]/Hβ diagnostic currently used by the community. They also have the advantage of attaching a probability that a given objectmore » belongs to one class or the other. Finally, we discuss briefly why ZQE diagrams can provide a new way to differentiate and study the different classes of AGNs in anticipation of a dedicated follow-up study.« less
Authors:
; ; ;  [1] ;  [2] ; ; ;  [3]
  1. Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 (Australia)
  2. Observatoire de Paris, LERMA (CNRS: UMR8112), 61 Av. de l'Observatoire, F-75014 Paris (France)
  3. Astronomy Department, King Abdulaziz University, P.O. Box 80203, Jeddah (Saudi Arabia)
Publication Date:
OSTI Identifier:
22370542
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 793; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CLASSIFICATION; DIAGRAMS; ELEMENT ABUNDANCE; EMISSION; EXCITATION; GALAXIES; GALAXY NUCLEI; METALLICITY; OXYGEN; PROBABILITY; SPACE; SPECTRA; THREE-DIMENSIONAL CALCULATIONS; TWO-DIMENSIONAL CALCULATIONS