Low frequency radio properties of the $z>5$ quasar population

A. J. Gloudemans, K. J. Duncan, H. J. A. Röttgering, T. W. Shimwell, B. P. Venemans, P. N. Best, M. Brüggen, G. Calistro Rivera, A. Drabent, M. J. Hardcastle, G. K. Miley, D. J. Schwarz, A. Saxena, D. J. B. Smith, W. L. Williams

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Optically luminous quasars at $z > 5$ are important probes of super-massive black hole (SMBH) formation. With new and future radio facilities, the discovery of the brightest low-frequency radio sources in this epoch would be an important new probe of cosmic reionization through 21-cm absorption experiments. In this work, we systematically study the low-frequency radio properties of a sample of 115 known spectroscopically confirmed $z>5$ quasars using the second data release of the Low Frequency Array (LOFAR) Two Metre Sky survey (LoTSS-DR2), reaching noise levels of $\sim$80 $\mu$Jy beam$^{-1}$ (at 144 MHz) over an area of $\sim5720$ deg$^2$. We find that 41 sources (36%) are detected in LoTSS-DR2 at $>2 \sigma$ significance and we explore the evolution of their radio properties (power, spectral index, and radio loudness) as a function of redshift and rest-frame ultra-violet properties. We obtain a median spectral index of $-0.29^{+0.10}_{-0.09}$ by stacking 93 quasars using LoTSS-DR2 and Faint Images of the Radio Sky at Twenty Centimetres (FIRST) data at 1.4 GHz, in line with observations of quasars at $z
Original languageEnglish
JournalAstronomy & Astrophysics
Publication statusAccepted/In press - 7 Oct 2021


  • astro-ph.GA


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