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The VMC survey - XLIX. Discovery of a population of quasars dominated by nuclear dust emission behind the Magellanic Clouds

Pennock, Clara M; Th van Loon, Jacco; Anih, Joy O; Maitra, Chandreyee; Haberl, Frank; Sansom, Anne E; Ivanov, Valentin D; Cowley, Michael J; Afonso, José; Antón, Sonia; Cioni, Maria-Rosa L; Craig, Jessica E M; Filipović, Miroslav D; Hopkins, Andrew M; Nanni, Ambra; Prandoni, Isabella; Vardoulaki, Eleni

The VMC survey - XLIX. Discovery of a population of quasars dominated by nuclear dust emission behind the Magellanic Clouds Thumbnail


Authors

Clara M Pennock

Joy O Anih

Chandreyee Maitra

Frank Haberl

Anne E Sansom

Valentin D Ivanov

Michael J Cowley

José Afonso

Sonia Antón

Maria-Rosa L Cioni

Jessica E M Craig

Miroslav D Filipović

Andrew M Hopkins

Ambra Nanni

Isabella Prandoni

Eleni Vardoulaki



Abstract

Following the discovery of SAGE0536AGN (z ∼ 0.14), with the strongest 10-μm silicate emission ever observed for an active galactic nucleus (AGN), we discovered SAGE0534AGN (z ∼ 1.01), a similar AGN but with less extreme silicate emission. Both were originally mistaken as evolved stars in the Magellanic Clouds. Lack of far-infrared emission, and therefore star formation, implies we are seeing the central engine of the AGN without contribution from the host galaxy. They could be a key link in galaxy evolution. We used a dimensionality reduction algorithm, t-distributed stochastic neighbour embedding with multiwavelength data from Gaia EDR3, VISTA survey of the Magellanic Clouds, AllWISE, and the Australian Square Kilometre Array Pathfinder to find these two unusual AGNs are grouped with 16 other objects separated from the rest, suggesting a rare class. Our spectroscopy at South African Astronomical Observatory/Southern African Large Telescope and literature data confirm at least 14 of these objects are extragalactic (0.13 < z < 1.23), all hosting AGN. Using spectral energy distribution fitter C igale we find that the majority of dust emission ($\gt 70 {{\ \rm per\ cent}}$) in these sources is due to the AGN. Host galaxies appear to be either in or transitioning into the green valley. There is a trend of a thinning torus, increasing X-ray luminosity, and decreasing Eddington ratio as the AGN transition through the green valley, implying that as the accretion supply depletes, the torus depletes and the column density reduces. Also, the near-infrared variability amplitude of these sources correlates with attenuation by the torus, implying the torus plays a role in the variability.

Journal Article Type Article
Acceptance Date Jul 22, 2022
Online Publication Date Jul 28, 2022
Publication Date 2022-10
Publicly Available Date May 30, 2023
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 515
Issue 4
Pages 6046-6065
DOI https://doi.org/10.1093/mnras/stac2096
Keywords Space and Planetary Science, Astronomy and Astrophysics
Publisher URL https://academic.oup.com/mnras/article/515/4/6046/6651397?login=true

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