# University of Hertfordshire

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

Research output: Contribution to journalArticlepeer-review

• 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
Original language English Astronomy & Astrophysics Accepted/In press - 7 Oct 2021

### Abstract

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

ID: 26108945