Powerful t-SNE technique leading to clear separation of type-2 AGN and HII galaxies in BPT diagrams

Abstract

Narrow emission-line galaxies can be distinguished in the well-known BPT diagrams through narrow emission line properties. However, there are no boundaries visible to the naked eye between type-2 AGN and HII galaxies in BPT diagrams, besides the extreme dividing lines expected by theoretical photoionization models. Here, based on powerful t-SNE technique applied to the local narrow emission-line galaxies in SDSS DR15, type-2 AGN and HII galaxies can be clearly separated in the t-SNE determined two-dimensional projected map, and then the dividing lines can be mathematically determined in BPT diagrams, leading to charming harmonization of the theoretical expectations and the actual results from real observed properties. The results not only provide an interesting and robust method to determine the dividing lines in BPT diagrams through the powerful t-SNE technique, but also lead to further confirmation on previously defined composite galaxies more efficiently classified in the BPT diagram of [OIII]/H$\beta$ versus [NII]/H$\alpha$.

9 pages, 5 figures, accepted to be published in ApJ

References in corpus (7)

• The Host Galaxies and Classification of Active Galactic Nuclei
• Understanding Galaxy Evolution through Emission Lines
• AGN Emission Line Diagnostics and the Mass-Metallicity Relation up to Redshift z~2: the Impact of Selection Effects and Evolution
• Estimation of stellar atmospheric parameters from SDSS/SEGUE spectra
• PCA Tomography: how to extract information from datacubes
• The Galah Survey: Classification and diagnostics with t-SNE reduction of spectral information
• Theoretical Modeling of Emission-Line galaxies: New Classification Parameters for Mid-Infrared and Optical Spectroscopy

Cited by in corpus (10)

• StarHorse results for spectroscopic surveys + Gaia DR3: Chrono-chemical populations in the solar vicinity, the genuine thick disk, and young-alpha rich stars
• Detecting gravitational lenses using machine learning: exploring interpretability and sensitivity to rare lensing configurations
• SDSS J1058+5443: A blue quasar does not have optical/NUV broad emission lines
• Systematic research of low redshift optically selected SDSS Type-2 AGN but with apparent long-term optical variabilities from Catalina Sky Survey, I: data sample and basic results
• How do supernova remnants cool? -- I. Morphology, optical emission lines, and shocks
• The VMC Survey -- XLIX. Discovery of a population of quasars dominated by nuclear dust emission behind the Magellanic Clouds
• A candidate of binary black hole system in AGN with broad Balmer emission lines having quite different line widths
• Long-term variability of the composite galaxy SDSS J103911-000057: A candidate of true Type-2 AGN
• Velocity offset between emission and absorption lines might be an effective indicator of dual core system
• How do supernova remnants cool? II. Machine learning analysis of supernova remnant simulations