{"work":{"id":"7268c38e-1ba4-4dfd-8342-ae65bb28c588","openalex_id":null,"doi":null,"arxiv_id":"1406.5186","raw_key":null,"title":"Galaxy emission line classification using 3D line ratio diagrams","authors":null,"authors_text":null,"year":2014,"venue":"astro-ph.GA","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 - HII-like or else 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 a specific set of 3D diagrams, the ZQE diagrams, which separate the oxygen abundance and the ionisation parameter of HII region-like spectra, and which also enable us to probe the excitation mechanism of the gas. By examining these new 3D spaces interactively, we define a new set of 2D diagnostics, the ZE diagnostics, which can provide the metallicity of objects excited by hot young stars, and which cleanly separate HII region-like objects from the different classes of AGNs. We show that these ZE diagnostics are consistent with the key log[NII]/H$\\alpha$ vs. log[OIII]/H$\\beta$ diagnostic currently used by the community. They also have the advantage of attaching a probability that a given object belongs to one class or to 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.","external_url":"https://arxiv.org/abs/1406.5186","cited_by_count":null,"metadata_source":"pith","metadata_fetched_at":"2026-05-23T03:12:28.298127+00:00","pith_arxiv_id":"1406.5186","created_at":"2026-05-14T18:17:34.598911+00:00","updated_at":"2026-05-23T03:12:28.298127+00:00","title_quality_ok":true,"display_title":null,"render_title":"Galaxy emission line classification using 3D line ratio diagrams"},"hub":{"state":{"work_id":"7268c38e-1ba4-4dfd-8342-ae65bb28c588","tier":"hub","tier_reason":"10+ Pith inbound or 1,000+ external citations","pith_inbound_count":12,"external_cited_by_count":null,"distinct_field_count":4,"first_pith_cited_at":"2025-02-17T10:15:22+00:00","last_pith_cited_at":"2026-05-20T07:26:59+00:00","author_build_status":"not_needed","summary_status":"needed","contexts_status":"needed","graph_status":"needed","ask_index_status":"not_needed","reader_status":"not_needed","recognition_status":"not_needed","updated_at":"2026-05-26T09:16:35.900794+00:00","tier_text":"hub"},"tier":"hub","role_counts":[{"context_role":"background","n":1}],"polarity_counts":[{"context_polarity":"background","n":1}],"runs":{},"summary":{},"graph":{},"authors":[]}}