The role of relativistic jets in the heaviest and most active supermassive black holes at high redshift

TL;DR

This paper discusses how relativistic jets are more common in the most massive black holes at high redshift, suggesting a link to black hole spin and accretion efficiency, with implications for black hole growth and evolution.

Contribution

It provides new observational evidence that relativistic jets are more prevalent in early universe supermassive black holes, highlighting the role of black hole spin and jet activity in their growth.

Findings

Relativistic jets are more frequent in massive black holes at high redshift.

The ratio of radio-loud to radio-quiet AGN varies strongly with redshift.

High spin and jet activity may inhibit rapid black hole growth.

Abstract

In powerful radio-quiet active galactic nuclei (AGN), black holes heavier than one billion solar masses form at a redshift ~1.5-2. Supermassive black holes in jetted radio-loud AGN seems to form earlier, at a redshift close to 4. The ratio of active radio-loud to radio-quiet AGN hosting heavy black holes is therefore a rather a strong function of redshift. We report on some recent evidence supporting this conclusion, gathered from the Burst Alert Telescope (BAT, onboard Swift) and by the Large Area Telescope (LAT, onboard Fermi). We suggest that the more frequent occurrence of relativistic jets in the most massive black holes at high redshifts, compared to later times, could be due to the average black hole spin being greater in the distant past, or else to the jet helping a fast accretion rate (or some combination of the two scenarios). We emphasize that the large total accretion efficiency of rapidly spinning black holes inhibits a fast growth, unless a large fraction of the available gravitational energy of the accreted mass is not converted into radiation, but used to form and maintain a powerful jet.