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Probing the roles of orientation and multiscale gas distributions in shaping the obscuration of active galactic nuclei through cosmic time

Alonso-Tetilla, Alba V; Shankar, Francesco; Fontanot, Fabio; Menci, Nicola; Valentini, Milena; Buchner, Johannes; Laloux, Brivael; Lapi, Andrea; Puglisi, Annagrazia; Alexander, David M; Allevato, Viola; Andonie, Carolina; Bonoli, Silvia; Hirschmann, Michaela; López, Iván E; Raimundo, Sandra I; Ramos Almeida, Cristina

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Alba V Alonso-Tetilla

Francesco Shankar

Fabio Fontanot

Nicola Menci

Milena Valentini

Johannes Buchner

Brivael Laloux
PGR Student Doctor of Philosophy

Andrea Lapi

Viola Allevato

Carolina Andonie

Silvia Bonoli

Michaela Hirschmann

Iván E López

Sandra I Raimundo

Cristina Ramos Almeida


The origin of obscuration in active galactic nuclei (AGNs) is still an open debate. In particular, it is unclear what drives the relative contributions to the line-of-sight column densities from galaxy-scale and torus-linked obscuration. The latter source is expected to play a significant role in Unification Models, while the former is thought to be relevant in both Unification and Evolutionary models. In this work, we make use of a combination of cosmological semi-analytic models and semi-empirical prescriptions for the properties of galaxies and AGN, to study AGN obscuration. We consider a detailed object-by-object modelling of AGN evolution, including different AGN light curves (LCs), gas density profiles, and also AGN feedback-induced gas cavities. Irrespective of our assumptions on specific AGN LC or galaxy gas fractions, we find that, on the strict assumption of an exponential profile for the gas component, galaxy-scale obscuration alone can hardly reproduce the fraction of log (NH/cm−2) ≥ 24 sources at least at z ≲ 3. This requires an additional torus component with a thickness that decreases with luminosity to match the data. The torus should be present in all evolutionary stages of a visible AGN to be effective, although galaxy-scale gas obscuration may be sufficient to reproduce the obscured fraction with 22 < log (NH/cm−2) < 24 (Compton-thin, CTN) if we assume extremely compact gas disc components. The claimed drop of CTN fractions with increasing luminosity does not appear to be a consequence of AGN feedback, but rather of gas reservoirs becoming more compact with decreasing stellar mass.

Journal Article Type Article
Acceptance Date Oct 20, 2023
Online Publication Date Oct 25, 2023
Publication Date 2024-02
Deposit Date Apr 11, 2024
Publicly Available Date Apr 11, 2024
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 527
Issue 4
Pages 10878-10896
Keywords Space and Planetary Science; Astronomy and Astrophysics
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Copyright Statement
© The Author(s) 2023
Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium,
provided the original work is properly cited.

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