Bridging diagnostics: Multi-wavelength consistency and discrepancy in the classification of local AGN

15 Sept 2026, 16:50
20m
Auditorium Telescopium (ESO)

Auditorium Telescopium

ESO

Regular AGN Emission

Speaker

Helene Kast

Description

Understanding the interplay between AGN and their host galaxies is central to modern galaxy evolution studies. As we move beyond isolated diagnostics toward a unified, multi-wavelength framework, understanding the reliability and limits of AGN classification methods becomes necessary for interpreting the feedback mechanisms that shape galaxies. We address this challenge by combining optical and X-ray AGN diagnostics: Specifically, the galaxy sample of the extended Calar-Alto Legacy Field spectroscopy Area (CALIFA) survey, an optical wide-field integral field unit survey of low redshift galaxies, and the Data Release 1 main source catalogue of the extended ROentgen Survey with an Imaging Telescope Array (eROSITA), a sensitive wide-field X-ray telescope. This yields a sample size of 254 potential AGN hosts in the local Universe. We use BPT diagrams and the WHaD diagram, both nuclear activity diagnostics based on optical emission line information, and perform a survey cross-matching to derive an X-ray AGN classification. The AGNs for which multiple classifications agree are identified, followed by a detailed inspection of the mechanisms behind their agreement/disagreement. 40% of the X-ray AGNs are classified as active in at least one of the optical classifications. Not only does the disagreement between classifications underscore the limitations of single-diagnostic approaches and suggests a complex temporal and geometric picture of AGN activity, global properties determined in iEDGE reveal a bias in the galaxy populations depending on classification. This work demonstrates the power of multiwavelength studies in contributing to the broader goal of reconciling diverse observational signatures into a consistent picture of AGN activity and its impact. I will also show preliminary findings doing a similar comparison in KILOGAS, allowing to investigate resolved gas properties and their relation to AGN feedback for a sample of unprecedented size.

Author

Co-authors

Dr Mallory Thorp (Argelander-Institut für Astronomie) Dr Dario Colombo (Argelander-Institut für Astronomie) Prof. Frank Bigiel (Argelander-Institut für Astronomie)

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