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BPT diagram

(diagram comparing emission-line ratios for characterizing ionization)

The BPT diagrams are three types of diagram that plot the relative strengths of emission lines with the aim of determining the state of ionization of a plasma, specifically for classifying active galactic nuclei (AGNs). Each of the three diagrams plots an [O III] line's ratio with H-β against another such ratio:

The plots are log-log. BPT is for Baldwin, Phillips & Terlevich, the three authors who introduced the diagrams.


(diagram,AGN,lines)
Further reading:
http://ned.ipac.caltech.edu/level5/Glossary/Essay_bpt.html
https://sites.google.com/site/agndiagnostics/agn-optical-line-diagnostics/bpt-diagrams
http://www.astro.gsu.edu/~crenshaw/15.AGN_Physics.pdf
https://ui.adsabs.harvard.edu/abs/1981PASP...93....5B/abstract

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