Abstract
A non-negligible fraction of quasars are red at optical wavelengths, indicating (in the majority of cases) that the accretion disc is obscured by a column of dust which extinguishes the shorter-wavelength blue emission. In this paper, we summarize recent work by our group, where we find fundamental differences in the radio properties of SDSS optically-selected red quasars. We also present new analyses, using a consistent color-selected quasar parent sample matched to four radio surveys (FIRST, VLA Stripe 82, VLA COSMOS 3 GHz, and LoTSS DR1) across a frequency range 144 MHz–3 GHz and four orders of magnitude in radio flux. We show that red quasars have enhanced small-scale radio emission (∼kpc) that peaks around the radio-quiet threshold (defined as the ratio of 1.4 GHz luminosity to 6 μm luminosity) across the four radio samples. Exploring the potential mechanisms behind this enhancement, we rule out star-formation and propose either small-scale synchrotron jets, frustrated jets, or dusty winds interacting with the interstellar medium; the latter two scenarios would provide a more direct connection between opacity (dust; gas) and the production of the radio emission. In our future study, using new multi-band uGMRT data, we aim to robustly distinguish between these scenarios.
Highlights
Quasi-stellar objects (QSOs), known as quasars, are the most powerful class of Active Galactic Nuclei (AGN)
We have recently found that Sloan Digital Sky Survey (SDSS) red QSOs show ∼2–3 times higher radiodetection fraction compared to typical blue QSOs, which cannot be explained via a simple orientation model [8,9,10,11]
We confirmed our previous radio results, finding an enhancement in the radiodetection fraction of rQSOs compared to cQSOs that arises in radio compact systems around the radio-quiet threshold [8,9,10,11]
Summary
Quasi-stellar objects (QSOs), known as quasars, are the most powerful class of Active Galactic Nuclei (AGN). We have recently found that Sloan Digital Sky Survey (SDSS) red QSOs show ∼2–3 times higher radiodetection fraction compared to typical blue QSOs, which cannot be explained via a simple orientation model [8,9,10,11]. This radio-detection enhancement is driven by red QSOs with compact radio morphologies (
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