Searcharxiv⌕ Search
Home/Archive/arXiv

arXiv · 2611.05353

Beyond just a torus? Re-contextualising the AGN type paradigm using data-driven host galaxy quenching histories

Sahyadri D. Krishna·Vivienne Wild·Paul C. Hewett·Victoria A. Fawcett·Omar Almaini·Carolin Villforth
View original source ↗Read source document ↗Export metadata ↓

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 $\sim$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 ($0.16 \leq z \leq 0.4$) and AGN luminosity ($6.5<\log_{10} [L_{[OIII]}/L_\odot] <9.5$). Using MFICA, we find that only $\sim$10 per cent of AGN host galaxies have recently ($\lesssim1$\,Gyr) and rapidly quenched star formation following a starburst, with Type-2 AGN host galaxies having done so at most 100\,Myrs more recently than Type-1 AGN host galaxies. For most ($\sim$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.

Explore related subjects

astro-ph.GA

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Sahyadri D. Krishna, Vivienne Wild, Paul C. Hewett, Victoria A. Fawcett, Omar Almaini, Carolin Villforth. 2026-11-03. Beyond just a torus? Re-contextualising the AGN type paradigm using data-driven host galaxy quenching histories. https://arxiv.org/abs/2611.05353

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

SDSS-V LVM: Revealing the Physical and Chemical Structure of the Helix Nebula

We present the first spatially contiguous study of the physical and chemical structure of the Helix Nebula (NGC~7293, PNG 036.1-57.1) based on integral-field spectroscopy from the SDSS-V Local Volume Mapper (LVM). The wide-field observations provide nearly complete spectroscopic coverage of the nebula, enabling a spaxel-by-spaxel analysis of extinction, electron density and temperature, ionisation structure, and chemical abundances. We reconstruct calibrated datacubes from the LVM row-stacked spectra and measure 41 optical emission lines, including hydrogen, helium, and collisionally excited metal lines. The resulting maps reveal a strongly stratified nebula, with highly ionised gas traced by \heii~concentrated toward the central cavity, low-ionisation material dominating the bright shell, and neutral or transition-zone gas enhanced in the outer regions. The Helix is a low-density object, with typical electron densities of $\sim10^{2}\mathrm{cm^{-3}}$, and exhibits a non-uniform temperature structure, with variations of several thousand Kelvin across different ionisation zones. We derive a near-solar oxygen abundance, $12+\log(\mathrm{O/H})\simeq8.7$, consistent with spatially complete sampling. The central abundance pattern indicates a significant contribution from unobserved O$^{3+}$, suggesting that apparent abundance variations are primarily driven by ionisation effects rather than true chemical inhomogeneities. We also find evidence for a sulfur deficit of $\sim$1 dex, consistent with the planetary-nebula sulfur anomaly. The helium and nitrogen abundances place the Helix near the classical boundary of Type~I planetary nebulae, suggesting moderate chemical enrichment by its progenitor star.

astro-ph.GA↗
arXiv2026

Infrared spectroscopy of gas-phase hydrogenated and methylated pyrenes: from laboratory spectra to the simulated 3.4 $μ$m emission band

Observations of the aromatic infrared emission band at 3.3 mic often reveal satellite emission features in the 3.4 - 3.6 mic range. While the 3.3 mic band is attributed to the CH stretching vibration of polycylic aromatic hydrocarbons (PAHs), the satellite bands - particularly its prominent 3.4 mic component - is assigned to aliphatic CH stretching vibrations in hydrogenated and methylated PAH-like species. Our aim is to derive state-of-the-art infrared emission spectra for aliphatic-containing pyrene derivatives and compare them with astronomical observations. This will help refine our understanding of the contribution of these species to the 3.4 mic emission band. Mid-infrared spectra (1.4-25 mic of gas-phase dihydropyrene, tehtrahydropyrene, hexahydropyrene methylated pyrene, and pyrene were recorded at temperatures ranging from 373 to 673 K, depending on the species. The band profiles were analyzed using a multi-component fitting tool, and empirical anharmonicity laws were derived to quantify the evolution of the band positions and widths with temperature. The obtained spectral data was combined with the results of a Monte Carlo emission model to simulate the emission spectra following UV-photon absorption, up to the dissociation limit (<6 eV). The resulting synthetic spectra were compared with James Webb Space Telescope observations of the Orion Bar region (PDRs4All program). Based on these state-of-the-art simulated spectra, we show that 1,2,3,6,7,8-hexahydropyrene matches all the constrains to fit the red component of the 3.4 mic band observed at 3.403 mic. While 1-methylpyrene may also contribute to the underlying emission plateau, its lack of a strong infrared band complicates detection in observed spectra, unlike hexahydropyrene. All experimental spectra and their temperature-dependent analyses are available in the new cosmicPAH-IRDB database.

astro-ph.GA↗
arXiv2026

Revealing a multi-zone circumnuclear dust response in UGC 11487 through phase-resolved WISE W1--W2 diagnostics

Mid-infrared (MIR) flares provide a direct probe of dust reprocessing in obscured tidal disruption event (TDE) candidates when the primary optical or ultraviolet flare is weak, missed, or strongly attenuated. We present a phase-resolved analysis of the WISE/NEOWISE W1-W2 evolution of the MIR-selected TDE candidate UGC 11487/WTP14adeqka over 2014-2024. We combine timing, colour, and flux diagnostics with phenomenological modelling, hydrodynamically motivated clumpy dust-echo calculations, and an aperture-matched ultraviolet-to-radio spectral energy distribution of the host. The decade-long flare shows a delayed and broader W2 response, colour hysteresis, and cooling from approximately 900 K to 500-600 K. Positive-fluence centroids yield a preferred delay of $224 +/- 45$ d, corresponding to $0.188 +/- 0.038$ pc. The effective infrared luminosity peaks at approximately $3 x 10^{43}$ erg s$^{-1}$, and the integrated infrared energy is $(2.9-3.8) x 10^{51}$ erg. A single self-similar MIR response is strongly disfavoured, with Delta BIC = 281.7, while the preferred compact description is a two-component phenomenological model. Representative hydro-clumpy calculations reproduce the empirical diagnostics in a structured, multi-zone dust-response scenario. The host is a moderately star-forming isolated barred disc without a dominant persistent active galactic nucleus component. These results support an obscured TDE-like accretion transient reprocessed by structured circumnuclear dust and show that phase-resolved WISE diagnostics can recover characteristic sub-parsec response scales in obscured accretion-powered nuclear transients.

astro-ph.GA↗