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Fundamental differences in the properties of red and blue quasars: measuring the reddening and accretion properties with X-shooter

Lookup NU author(s): Dr Vicky FawcettORCiD, Dr David Rosario



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


We have recently found fundamental differences in the radio properties of red quasars when compared to typical blue quasars. In this paper, we use data from the X-shooter spectrograph on the Very Large Telescope, providing spectral coverage from ∼3000–25000 Å, of a sample of 40 red and blue luminous quasars at 1.45 < z < 1.65 to explore the connections between the radio, emission-line, and accretion-disc properties. We fit various dust-extinction curves to the data and find that dust reddening can fully explain the observed colours for the majority of the red quasars in our sample, with moderate extinctions ranging from AV ∼ 0.06–0.7 mag. We confront our spectra with a simple thin accretion-disc model and find this can describe the continua of both the blue and red quasars, once corrected for dust extinction; we also find no significant differences in the accretion properties. We detect ionized outflows in a number of red and blue quasars, but do not find any significant evidence that they are more prevalent in the red quasar population. Overall our findings imply that the radio emission is more closely connected to circumnuclear/ISM opacity rather than accretion disc or outflow differences.

Publication metadata

Author(s): Fawcett VA, Alexander DM, Rosario DJ, Klindt L, Lusso E, Morabito LK, Calistro Rivera G

Publication type: Article

Publication status: Published

Journal: Monthly Notices of the Royal Astronomical Society

Year: 2022

Volume: 513

Issue: 1

Pages: 1254–1274

Print publication date: 01/06/2022

Online publication date: 13/04/2022

Acceptance date: 29/03/2022

Date deposited: 27/06/2023

ISSN (print): 0035-8711

ISSN (electronic): 1365-2966

Publisher: Oxford University Press


DOI: 10.1093/mnras/stac945


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Funder referenceFunder name
Alfred P. Sloan Foundation
Higher Education Funding Council for England
Max Planck Society
National Science Foundation
National Aeronautics and Space Administration
Participating Institutions
U.S. Department of Energy