Fundamental differences in the radio properties of red and blue quasars: Insight from the LOFAR Two-metre Sky Survey (LoTSS)

Abstract

Red quasi-stellar objects (QSOs) are a subset of the luminous end of the cosmic population of active galactic nuclei (AGN), most of which are reddened by intervening dust along the line-of-sight towards their central engines. In recent work from our team, we developed a systematic technique to select red QSOs from the Sloan Digital Sky Survey (SDSS), and demonstrated that they have distinctive radio properties using the Faint Images of the Radio Sky at Twenty centimeters (FIRST) radio survey. Here we expand our study using low-frequency radio data from the LOFAR Two-metre Sky Survey (LoTSS). With the improvement in depth that LoTSS offers, we confirm key results: compared to a control sample of normal "blue" QSOs matched in redshift and accretion power, red QSOs have a higher radio detection rate and a higher incidence of compact radio morphologies. For the first time, we also demonstrate that these differences arise primarily in sources of intermediate radio-loudness: radio-intermediate red QSOs are $\times 3$ more common than typical QSOs, but the excess diminishes among the most radio-loud and the most radio-quiet systems in our study. We develop Monte-Carlo simulations to explore whether differences in star formation could explain these results, and conclude that, while star formation is an important source of low-frequency emission among radio-quiet QSOs, a population of AGN-driven compact radio sources is the most likely cause for the distinct low-frequency radio properties of red QSOs. Our study substantiates the conclusion that fundamental differences must exist between the red and normal blue QSO populations.

20 pages, 16 Figures. Accepted for publication in MNRAS

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• The radio loudness of SDSS quasars from the LOFAR Two-metre Sky Survey: ubiquitous jet activity and constraints on star formation
• The multiwavelength properties of red QSOs -- Evidence for dusty winds as the origin of QSO reddening
• Fundamental differences in the radio properties of red and blue quasars: enhanced compact AGN emission in red quasars
• Discovery of 24 radio-bright quasars at $4.9\le z\le 6.6$ using low-frequency radio observations
• 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
• LeMMINGs. III. The e-MERLIN Legacy Survey of the Palomar sample. Exploring the origin of nuclear radio emission in active and inactive galaxies through the [O III] -- radio connection
• Fundamental differences in the properties of red and blue quasars: measuring the reddening and accretion properties with X-shooter
• 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
• Connecting radio emission to AGN wind properties with Broad Absorption Line Quasars
• 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 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?
• VLA Snapshot Continuum Survey of FRI Quasar Candidates Selected from the LOFAR Two-Metre Sky Survey (LoTSS)
• Improved selection of extremely red quasars with boxy CIV lines in BOSS
• How are Red and Blue Quasars Different? The Radio Properties
• What is the origin of the stacked radio emission in radio-undetected quasars?: Insights from a radio-infrared image stacking analysis
• Probing the Wind Component of Radio Emission in Luminous High-Redshift Quasars
• Evidence for radio loud to radio quiet evolution from red and blue quasars
• The Nature of LoBAL QSOs: II. HST/WFC3 Observations Reveal Host Galaxies Dominated by Mergers
• Exploring the quasar disc-wind-jet connection with LoTSS and SDSS
• The dependence of the fraction of radio luminous quasars on redshift and its theoretical implications