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Obscuration beyond the nucleus: infrared quasars can be buried in extreme compact starbursts

Lookup NU author(s): Dr Chris HarrisonORCiD, Dr David RosarioORCiD

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).

Abstract

© The Author(s) 2023. In the standard quasar model, the accretion disc obscuration is due to the canonical dusty torus. Here, we argue that a substantial part of the quasar obscuration can come from the interstellar medium (ISM) when the quasars are embedded in compact starbursts. We use an obscuration-unbiased sample of 578 infrared (IR) quasars at z ≈ 1–3 and archival Atacama Large Millimetre/submillimetre Array submillimetre host galaxy sizes to investigate the ISM contribution to the quasar obscuration. We calculate star formation rates (SFR) and ISM column densities for the IR quasars and a control sample of submillimetre galaxies (SMGs) not hosting quasar activity and show that: (1) the quasar obscured fraction is constant up to SFR ≈ 300 M☉ yr−1, and then increases towards higher SFR, suggesting that the ISM obscuration plays a significant role in starburst host galaxies, and (2) at SFR ≳ 300 M☉ yr−1, the SMGs and IR quasars have similarly compact submillimetre sizes (Re ≈ 0.5–3 kpc) and consequently, the ISM can heavily obscure the quasar, even reaching Compton-thick (NH > 1024 cm−2) levels in extreme cases. Based on our results, we infer that ≈10–30 per cent of the IR quasars with SFR ≳ 300 M☉ yr−1 are obscured solely by the ISM.

Publication metadata

Author(s): Andonie C, Alexander DM, Greenwell C, Puglisi A, Laloux B, Alonso-Tetilla AV, Rivera GC, Harrison C, Hickox RC, Kaasinen M, Lapi A, Lopez IE, Petter G, Almeida CR, Rosario DJ, Shankar F, Villforth C

Publication type: Article

Publication status: Published

Journal: Monthly Notices of the Royal Astronomical Society: Letters

Year: 2024

Volume: 527

Issue: 1

Pages: L144-L150

Print publication date: 01/01/2024

Online publication date: 06/10/2023

Acceptance date: 02/10/2023

Date deposited: 14/08/2024

ISSN (print): 1745-3925

ISSN (electronic): 1745-3933

Publisher: Oxford University Press

URL: https://doi.org/10.1093/mnrasl/slad144

DOI: 10.1093/mnrasl/slad144

Data Access Statement: The data sets generated and/or analysed in this study are available from the corresponding author on reasonable request.

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