3D Astrophysics Newsletter

Vogt et al., 2015

3D-printed diagnostic diagram. Click on image for the interactive 3D HTML version  (image used with permission by the author, external link to ApJ website)

1.3. Today’s new entry:

Galaxy Emission Line Classification Using Three-dimensional Line Ratio Diagrams

Vogt, F.P.A., Dopita, M.A., Kewley, L.J., Sutherland, R.S., Scharwächter, J., Basurah, H.M., Ali, A., Amer, M.A.

Abstract: 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]/Halpha versus log [O III]/Hbeta diagnostic currently used by the community. They also have the advantage of attaching a probability that a given object 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.

Journal: The Astrophysical Journal, in press
URL of preprint: http://arxiv.org/abs/1406.5186
Comments: Interactive 3D HTML model is here:
Submitted by: Frédéric Vogt


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