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 10 10 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?

Exploring the radio spectral energy distribution of the ultraluminous radio-quiet quasar SDSS J0100+2802 at redshift 6.3

“…The fit to the data in 2016 yields a power-law spectral index of α 2016 = −0.21±0.10. We note that the L-band measurement we obtained is slightly lower than the value of 154 ± 12 µJy published in Sbarrato et al (2021), but is still marginally consistent considering the uncertainties. This is likely to be due to the difference in calibration and imaging methods.…”

“…This is likely to be due to the difference in calibration and imaging methods. Although a tentative jet is reported in Sbarrato et al (2021), there is no sign of extended structures with SNR>3 in our 1.5 GHz and 10 1 10 0 10 1…”

“…J0100+2802 was also observed at 1.5 GHz (L-band) and 5 GHz (C-band) in 2016 (program 16A-242), and the results are published in Sbarrato et al (2021). The L-band observation in 2016 was carried out in B configuration, and the C-band observations was in C configuration.…”

“…We consider that both time variability and emission from different scales may contribute to the discrepant flux density between the VLA and VLBA measurements at 1.5 GHz. While the compact radio core emission detected by both VLA and VLBA is likely to be dominated by the central luminous AGN (Wang et al 2017;Sbarrato et al 2021) the radio emission at larger scale maybe from a more diffuse component powered by AGN wind and/ or low-surface brightness knots of weak jets. Nuclear star forming activity could also contribute to the diffuse radio emission on kpc scale.…”

Blazar nature of high-z radio-loud quasars

“…If these samples were complete, we should conclude that most > 10 9 M black holes at z > 4 are hosted in jetted quasars, in spite of their radio-loudness. Note that 10 10 M z>5 quasars have already proved to host relativistic jets even when they are radio-quiet or when they completely lack standard jet signatures (Sbarrato et al 2021). At high redshifts, the same behaviour might extend toward smaller masses (but still above a billion M ), even only for a substantial fraction of them.…”