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Fundamental differences in the radio properties of red and blue quasars: kiloparsec-scale structures revealed by e-MERLIN

Rosario, D J and Alexander, D M and Moldon, J and Klindt, L and Thomson, A P and Morabito, L and Fawcett, V A and Harrison, C M (2021) 'Fundamental differences in the radio properties of red and blue quasars: kiloparsec-scale structures revealed by e-MERLIN.', Monthly notices of the Royal Astronomical Society, 505 (4). pp. 5283-5300.


Red quasi-stellar objects (QSOs) are a subset of the quasar population with colours consistent with reddening due to intervening dust. Recent work has demonstrated that red QSOs show special radio properties that fundamentally distinguish them from normal blue QSOs, specifically a higher incidence of low-power radio emission (1.4 GHz luminosities L1.4 ≈ 1025–1027 W Hz−1) that is physically compact when imaged by arcsecond-resolution radio surveys such as FIRST. In this work, we present e-MERLIN imaging of a set of intermediate-redshift (1.0 < z < 1.55), luminous (bolometric luminosities Lbol ≈ 1046–1047 erg s−1) red and normal QSOs carefully selected to have radio properties that span the range over which red QSOs show the most divergence from the general population. With an angular resolution 25× better than FIRST, we resolve structures within the host galaxies of these QSOs (>2 kpc). We report a statistically significant difference in the incidence of extended kpc-scale emission in red QSOs. From an analysis of the radio size distributions of the sample, we find that the excess radio emission in red QSOs can be attributed to structures that are confined to galaxy scales (<10 kpc), while we confirm previous results that red and normal QSOs have similar incidences of radio jets and lobes on circumgalactic or larger scales (>10 kpc). Our results indicate that the primary mechanism that generates the enhanced radio emission in red QSOs is not directly connected with the nuclear engine or accretion disc, but is likely to arise from extended components such as AGN-driven jets or winds.

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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2021 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:04 June 2021
Date deposited:14 July 2021
Date of first online publication:10 June 2021
Date first made open access:14 July 2021

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