Fundamental differences in the radio properties of red and blue quasars: enhanced compact AGN emission in red quasars

Abstract

We have recently used the Faint Images of the Radio Sky at Twenty-centimeters (FIRST) survey to show that red quasars have fundamentally different radio properties to typical blue quasars: a significant (factor $\sim 3$) enhancement in the radio-detection fraction, which arises from systems around the radio-quiet threshold with compact ($<5^{\prime \prime }$) radio morphologies. To gain greater insight into these physical differences, here we use the DR14 Sloan Digital Sky Survey (SDSS) and more sensitive, higher resolution radio data from the Very Large Array (VLA) Stripe 82 (S82) and VLA-COSMOS 3 GHz (C3GHz) surveys. With the S82 data, we perform morphological analyses at a resolution and depth three times that of the FIRST radio survey, and confirm an enhancement in radio-faint and compact red quasars over typical quasars; we now also find tentative evidence for an enhancement in red quasars with slightly extended radio structures ($16-43$ kpc at $z=1.5$). These analyses are complemented by C3GHz, which is deep enough to detect radio emission from star-formation processes. From our data we find that the radio enhancement from red quasars is due to AGN activity on compact scales ($<43$ kpc) for radio-intermediate-radio-quiet sources ($-5<R<-3.4$, where $R=L_{1.4GHz}/L_{6\mu m}$), which decreases at $R<-5$ as the radio emission from star-formation starts to dilute the AGN component. Overall our results argue against a simple orientation scenario and are consistent with red quasars representing a younger, earlier phase in the overall evolution of quasars.

17 pages, 17 Figures. Accepted for publication in MNRAS

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• Accretion mode versus radio morphology in the LOFAR Deep Fields
• The radio loudness of SDSS quasars from the LOFAR Two-metre Sky Survey: ubiquitous jet activity and constraints on star formation
• Discovery of 24 radio-bright quasars at $4.9\le z\le 6.6$ using low-frequency radio observations
• Fundamental differences in the radio properties of red and blue quasars: Insight from the LOFAR Two-metre Sky Survey (LoTSS)
• A panchromatic view of infrared quasars: excess star formation and radio emission in the most heavily obscured systems
• Red quasars blow out molecular gas from galaxies during the peak of cosmic star formation
• Fundamental differences in the radio properties of red and blue quasars: kiloparsec-scale structures revealed by e-MERLIN
• Placing LOFAR-detected quasars in CIV emission space: implications for winds, jets and star formation
• A novel Bayesian approach for decomposing the radio emission of quasars: I. Modelling the radio excess in red quasars
• Host Dark Matter Halos of SDSS Red and Blue Quasars: No Significant Difference in Large-scale Environment
• How does the radio enhancement of broad absorption line quasars relate to colour and accretion rate?
• Evidence for radio loud to radio quiet evolution from red and blue quasars