Jetted radio-quiet quasars at z>5

Abstract

We report on the JVLA observations of three high redshift Active Galactic Nuclei (AGN), having a black hole mass estimated to be among the largest known. Two of them, SDSS J0100+2802 and SDSS J0306+1853 at redshift 6.326 and 5.363 respectively, are radio–quiet AGN according to the classic definition, while the third (B2 1023+25 at z = 5.284) is a powerful blazar. The JVLA data clearly show a radio structure in the first source, and a radio emission with a relatively steep radio spectrum in the second one, demonstrating the presence of a radio jet and a diffuse component. Therefore, being radio–quiet does not exclude the presence of a powerful relativistic jet with important consequences on the population studies and on the ratio between jetted and non–jetted AGN. We can estimate the viewing angle of these jets, and this allows us to find, albeit with some uncertainty, the density of black holes with a mass in excess of 1010 M at high redshifts. We found that their density in jetted AGN is very large in the redshift bin 5–6, comparable with the overall AGN population of the same optical luminosity. Jets might thus play a crucial role in the fast formation and evolution of the most massive black holes in the early Universe. They are more common than what expected from wide radio surveys with mJy flux sensitivity. Deeper JVLA or VLBI observations are key to discover a possible relativistic jet population hiding in plain sight at very high–redshift. The discovery of powerful relativistic jets associated with the most massive black holes in the early Universe re-opens the question: is the jet instrumental for a rapid growth of the black hole or instead is the black hole mass the main driver for the jet formation?