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A panchromatic view of infrared quasars: excess star formation and radio emission in the most heavily obscured systems

Andonie, Carolina; Alexander, David M; Rosario, David; Laloux, Brivael; Georgakakis, Antonis; Morabito, Leah K; Villforth, Carolin; Avirett-Mackenzie, Mathilda; Rivera, Gabriela Calistro; Del Moro, Agnese; Fotopoulou, Sotiria; Harrison, Chris; Lapi, Andrea; Petley, James; Petter, Grayson; Shankar, Francesco

A panchromatic view of infrared quasars: excess star formation and radio emission in the most heavily obscured systems Thumbnail


David Rosario

Brivael Laloux

Antonis Georgakakis

Carolin Villforth

Mathilda Avirett-Mackenzie

Gabriela Calistro Rivera

Agnese Del Moro

Sotiria Fotopoulou

Chris Harrison

Andrea Lapi

James Petley
PGR Student Doctor of Philosophy

Grayson Petter

Francesco Shankar


To understand the active galactic nuclei (AGNs) phenomenon and their impact on the evolution of galaxies, a complete AGN census is required; however, finding heavily obscured AGNs is observationally challenging. Here we use the deep and extensive multiwavelength data in the COSMOS field to select a complete sample of 578 infrared (IR) quasars (LAGN,IR > 1045 erg s−1) at z < 3, with minimal obscuration bias, using detailed UV-to-far-IR spectral energy distribution (SED) fitting. We complement our SED constraints with X-ray and radio observations to further investigate the properties of the sample. Overall, 322 of the IR quasars are detected by Chandra and have individual X-ray spectral constraints. From a combination of X-ray stacking and L2−10 kev – L6 μm analyses, we show that the majority of the X-ray faint and undetected quasars are heavily obscured (many are likely Compton thick), highlighting the effectiveness of the mid-IR band to find obscured AGNs. We find that 355 (≈61 per cent) IR quasars are obscured (NH > 1022 cm−2) and identify differences in the average properties between the obscured and unobscured quasars: (1) obscured quasars have star formation rates ≈3 times higher than unobscured systems for no significant difference in stellar mass and (2) obscured quasars have stronger radio emission than unobscured systems, with a radio-loudness parameter ≈ 0.2 dex higher. These results are inconsistent with a simple orientation model but in general agreement with either extreme host-galaxy obscuration towards the obscured quasars or a scenario where obscured quasars are an early phase in the evolution of quasars.

Journal Article Type Article
Acceptance Date Sep 26, 2022
Online Publication Date Oct 3, 2022
Publication Date 2022-12
Deposit Date Oct 20, 2022
Publicly Available Date Oct 26, 2022
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 517
Issue 2
Pages 2577-2598
Public URL


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Copyright Statement
© 2022 The Author(s). 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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