EMU/GAMA: A Technique for Detecting Active Galactic Nuclei in Low Mass Systems
arxiv(2024)
Abstract
We propose a new method for identifying active galactic nuclei (AGN) in low
mass (M_*≤10^10M_⊙) galaxies. This method relies on spectral
energy distribution (SED) fitting to identify galaxies whose radio flux density
has an excess over that expected from star formation alone. Combining data in
the Galaxy and Mass Assembly (GAMA) G23 region from GAMA, Evolutionary Map of
the Universe (EMU) early science observations, and Wide-field Infrared Survey
Explorer (WISE), we compare this technique with a selection of different AGN
diagnostics to explore the similarities and differences in AGN classification.
We find that diagnostics based on optical and near-infrared criteria (the
standard BPT diagram, the WISE colour criterion, and the mass-excitation, or
MEx diagram) tend to favour detection of AGN in high mass, high luminosity
systems, while the “ProSpect” SED fitting tool can identify AGN efficiently
in low mass systems. We investigate an explanation for this result in the
context of proportionally lower mass black holes in lower mass galaxies
compared to higher mass galaxies and differing proportions of emission from AGN
and star formation dominating the light at optical and infrared wavelengths as
a function of galaxy stellar mass. We conclude that SED-derived AGN
classification is an efficient approach to identify low mass hosts with low
radio luminosity AGN.
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