Abstract
ABSTRACT 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.
Highlights
Quasi-stellar objects (QSOs) are the luminous tail of the population of active galactic nuclei (AGNs) and account for a substantial part of the cosmic mass growth in supermassive black holes (SMBHs)
Using images from the 1.4 GHz VLA/Stripe82 survey, we demonstrated that red QSOs (rQSOs) show a slight excess of radio sources with sizes that were close to the resolution limit (≈1.8 arcsec; ≈15 kpc at z ∼ 1)
We present e-MERLIN L-band images of a sample of red quasi-stellar objects (QSOs) and normal QSOs at redshifts of 1.0 < z < 1.55
Summary
Quasi-stellar objects (QSOs) are the luminous tail of the population of active galactic nuclei (AGNs) and account for a substantial part of the cosmic mass growth in supermassive black holes (SMBHs). Their distinctive features, high optical luminosities and clear spectroscopic signatures of broad emission lines, are the manifestation of an unimpaired line-of-sight view towards the central accretion engine and its immediate environment. The majority of QSOs have blue ultraviolet-to-optical colours consistent with direct thermal emission from an AGN accretion disc peaking in the extreme ultraviolet (effective temperatures ∼105 K). Large spectroscopic surveys, such as the Sloan Digital Sky Survey (SDSS), have identified a subset of QSOs that scatter to much redder
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