SEMINÁRIO DO DEPARTAMENTO DE ASTRONOMIA
Identifying AGNs from X-ray Detections: Resolving Systematic Biases in Metallicity Calibrations
a talk by Mark Armah (Universidade do Vale do Paraíba - UNIVAP/Brasil) - In-Person
Abstract:
"Traditional strong-line metallicity calibrations are often inherently biased by the AGN radiation field, complicating our understanding of galaxy evolution and metal content. To resolve this, we introduce new semi-empirical metallicity calibrations designed to decouple true chemical abundances from structural nebular variations. In the first phase we established a framework using comprehensive CLOUDY photoionization models explicitly parameterized by intrinsic 2-10 keV X-ray luminosity, evaluating the standard N₂ and O₃N₂ indices. Building upon this foundation, our subsequent work introduces highly optimized calibrations for the N₂O₂ and N₂S₂ diagnostics. By tracing co-spatial emitting volumes within the narrow-line regions (NLRs), these specific indices successfully resolve the X-ray luminosity-driven systematic biases previously identified, providing highly precise and unbiased metallicity constraints for AGNs."
Short-Bio:
Mark Armah is a FAPESP Postdoctoral Researcher at the Universidade do Vale do Paraíba (UNIVAP) in Brazil. His academic journey bridges engineering and astrophysics. He earned his BSc in Mechanical Engineering from the University of Mines and Technology (UMaT) in Ghana in 2013. He then pursued his transition to astrophysics, completing his MSc in Physics and Astronomy at UNIVAP in 2020, focusing on the chemical abundances of Seyfert 2 galaxies based on optical and IR emissions. In 2025, he received his PhD in Astrophysics from the Universidade Federal do Rio Grande do Sul (UFRGS), where his thesis investigated gas-phase metallicity in Seyfert galaxies. Today, his research explores the chemical composition of galaxies hosting active galactic nuclei (AGNs), investigating the complex interplay between supermassive black hole accretion and the physical properties of the surrounding gas.
Google Meet: https://meet.google.com/pcw-gmem-jyi
Link da transmissão: https://www.youtube.com/c/AstronomiaIAGUSP/live