How are Red and Blue Quasars Different? The Radio Properties

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 micron 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.

arXiv comment16 pages, 8 figures, 1 table, accepted by Galaxies for the special issue "A New Window on the Radio Emission from Galaxies, Galaxy Clusters and Cosmic Web: Current Status and Perspectives"

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• Fundamental differences in the properties of red and blue quasars: measuring the reddening and accretion properties with X-shooter
• Ubiquitous radio emission in quasars: predominant AGN origin and a connection to jets, dust and winds
• Powerful Radio-Loud Quasars are Triggered by Galaxy Mergers in the Cosmic Bright Ages
• A Treasure Hunt in the Pool of Spectra Classified as High-redshift QSOs by the Spectroscopic Pipeline of the SDSS DR16