Beyond BPT: A New Multidimensional Diagnostic Diagram for Classifying Power Sources Tested Using the SAMI Galaxy Survey

Current methods of identifying the ionizing source of nebular emission in galaxies are well defined for the era of single-fiber spectroscopy, but still struggle to differentiate the complex and overlapping ionization sources in some galaxies. With the advent of integral field spectroscopy, the limit...

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Bibliographic Details
Published in:The Astrophysical Journal
Main Authors: Victor D. Johnston, Anne M. Medling, Brent Groves, Lisa J. Kewley, Luca Cortese, Scott Croom, Ángel R. López-Sánchez, Henry Zovaro, Joss Bland-Hawthorn, Julia Bryant, Jon Lawrence, Matt Owers, Samuel Richards, Jesse van de Sande
Format: Article in Journal/Newspaper
Language:English
Published: IOP Publishing 2023
Subjects:
Warm ionized medium
Classification systems
Galaxy classification systems
Active galactic nuclei
Shocks
Star formation
Astrophysics
QB460-466
sami
Online Access:https://doi.org/10.3847/1538-4357/ace90e
https://doaj.org/article/cb9cf2dfa4754a57a7e3cbf9cece7ebb
Description
Summary:Current methods of identifying the ionizing source of nebular emission in galaxies are well defined for the era of single-fiber spectroscopy, but still struggle to differentiate the complex and overlapping ionization sources in some galaxies. With the advent of integral field spectroscopy, the limits of these previous classification schemes are more apparent. We propose a new method for distinguishing the ionizing source in resolved galaxy spectra by use of a multidimensional diagnostic diagram that compares emission-line ratios with velocity dispersion on a spaxel-by-spaxel basis within a galaxy. This new method is tested using the Sydney-Australian-Astronomical-Observatory Multi-object Integral-Field Spectrograph Galaxy Survey (SAMI) Data Release 3 (DR3), which contains 3068 galaxies at z < 0.12. Our results are released as ionization maps available alongside the SAMI DR3 public data. Our method accounts for a more diverse range of ionization sources than the standard suite of emission-line diagnostics; we find 1433 galaxies with a significant contribution from non-star-forming ionization using our improved method as compared to 316 galaxies identified using only emission-line ratio diagnostics. Within these galaxies, we further identify 886 galaxies hosting unique signatures inconsistent with standard ionization by H ii regions, active galactic nuclei, or shocks. These galaxies span a wide range of masses and morphological types and comprise a sizable portion of the galaxies used in our sample. With our revised method, we show that emission-line diagnostics alone do not adequately differentiate the multiple ways to ionize gas within a galaxy.

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