Beyond just a torus? Re-contextualising the AGN type paradigm using data-driven host galaxy quenching histories
Abstract
The orientation of a dusty torus within a unified model explains the presence (Type-1) or absence (Type-2) of broad emission lines in Active Galactic Nuclei (AGN) spectra. This orientation-based unified model, however, fails to explain differences in host galaxy properties, such as star formation rates, of Type-1 and Type-2 AGNs. Star-formation histories (SFHs) can shed light on the connection between AGN type and host galaxy properties, but are challenging to extract from Type-1 AGN that outshine their host galaxies. We use mean-field independent component analysis (MFICA) spectrum decomposition to extract the stellar populations of ∼3000 optically selected Type-1 and Type-2 AGN host galaxies from the seventh data release (DR7) of the Sloan Digital Sky Survey (SDSS), matched in redshift (0.16 ≤ z ≤ 0.4) and AGN luminosity (6.5<log10 [L[OIII]/L⊙] <9.5). Using MFICA, we find that only ∼10 per cent of AGN host galaxies have recently (≲1\,Gyr) and rapidly quenched star formation following a starburst, with Type-2 AGN host galaxies having done so at most 100\,Myrs more recently than Type-1 AGN host galaxies. For most (∼90 per cent) AGN hosts with normal recent star formation histories, Type-2 AGNs are associated with slightly younger stellar populations than Type-1 AGNs. The younger stellar populations of Type-2 AGN hosts can be explained by a link between dusty torus covering factors and stellar populations, by host-galaxy obscuration of AGN, or by an evolution in AGN type without major bursts or rapid quenching of star formation.
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BibTeX
@misc{krishna2026beyond,
title = {{Beyond just a torus? Re-contextualising the AGN type paradigm using data-driven host galaxy quenching histories}},
author = {Sahyadri D. Krishna and Vivienne Wild and Paul C. Hewett and Victoria A. Fawcett and Omar Almaini and Carolin Villforth},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.05353},
eprint = {2611.05353},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.05353},
}
RIS
TY - UNPB
TI - Beyond just a torus? Re-contextualising the AGN type paradigm using data-driven host galaxy quenching histories
AU - Sahyadri D. Krishna
AU - Vivienne Wild
AU - Paul C. Hewett
AU - Victoria A. Fawcett
AU - Omar Almaini
AU - Carolin Villforth
PY - 2026
DA - 2026/11/03
PB - arXiv
DO - 10.48550/arxiv.2611.05353
UR - https://arxiv.org/abs/2611.05353
AB - The orientation of a dusty torus within a unified model explains the presence (Type-1) or absence (Type-2) of broad emission lines in Active Galactic Nuclei (AGN) spectra. This orientation-based unified model, however, fails to explain differences in host galaxy properties, such as star formation rates, of Type-1 and Type-2 AGNs. Star-formation histories (SFHs) can shed light on the connection between AGN type and host galaxy properties, but are challenging to extract from Type-1 AGN that outshine their host galaxies. We use mean-field independent component analysis (MFICA) spectrum decomposition to extract the stellar populations of ∼3000 optically selected Type-1 and Type-2 AGN host galaxies from the seventh data release (DR7) of the Sloan Digital Sky Survey (SDSS), matched in redshift (0.16 ≤ z ≤ 0.4) and AGN luminosity (6.5<log_10 [L_[OIII]/L_⊙] <9.5). Using MFICA, we find that only ∼10 per cent of AGN host galaxies have recently (≲1\,Gyr) and rapidly quenched star formation following a starburst, with Type-2 AGN host galaxies having done so at most 100\,Myrs more recently than Type-1 AGN host galaxies. For most (∼90 per cent) AGN hosts with normal recent star formation histories, Type-2 AGNs are associated with slightly younger stellar populations than Type-1 AGNs. The younger stellar populations of Type-2 AGN hosts can be explained by a link between dusty torus covering factors and stellar populations, by host-galaxy obscuration of AGN, or by an evolution in AGN type without major bursts or rapid quenching of star formation.
ER -