The radio-loud fraction of quasars at z 6

Quasars at redshifts z>6 are an excellent probe of the formation and evolution of supermassive black holes in the early Universe. The population of radio-luminous quasars is of particular interest, as such quasars could potentially be used to study the neutral intergalactic medium during cosmic reionisation via H\, I 21\, cm absorption studies. However, the lack of deep radio observations of z>6 quasars leaves the population poorly constrained, and suitable candidates for an H\, I 21\, cm absorption study have yet to be found. In this work, we present Jansky Very Large Array (VLA) 1-2 GHz radio continuum observations of 138 quasars at redshifts 6. 0 z6, which have previously been characterised in the literature at these frequencies. Using the full sample, we estimate the radio-loud fraction to be 3. 8^+6. 2-₂. ₄\%, where the uncertainties are 95% confidence intervals. This is lower than recent estimates of the radio-loud fraction in the literature, but is still marginally consistent with no redshift evolution of the radio-loud fraction. We explore the undetected quasar population by stacking their continuum images at their optical positions and obtain a median stacked flux density of 13. 8 3. 9~Jy and luminosity of L₅~₆₇ₙ/ (ₖ~₇ₙ^-₁) =24. 20. 1.