On the efficiency of jet production in FR II radio galaxies and quasars

TL;DR

This paper investigates why jets in FR II radio galaxies and quasars are more powerful than current models predict, suggesting that accretion disks might be thicker or simulations may oversimplify the physics.

Contribution

It provides observational evidence that jet powers exceed MAD scenario predictions, challenging existing theoretical models.

Findings

Jets are more powerful than MAD predictions.

Discrepancy may be due to disk thickness or simulation limitations.

Suggests need for revised models of accretion disk structure.

Abstract

Jet powers in many radio galaxies with extended radio structures appear to exceed their associated accretion luminosities. In systems with very low accretion rates, this is likely due to the very low accretion luminosities resulting from radiatively inefficient accretion flows. In systems with high accretion rates, the accretion flows are expected to be radiatively efficient, and the production of such powerful jets may require an accretion scenario which involves magnetically arrested discs (MADs). However, numerical simulations of the MAD scenario indicate that jet production efficiency is large only for geometrically thick accretion flows and scales roughly with $(H/R)^2$, where $H$ is the disc height and $R$ is the distance from the BH. Using samples of FRII radio galaxies and quasars accreting at moderate accretion rates we show that their jets are much more powerful than predicted by the MAD scenario. We discuss possible origins of this discrepancy, suggesting that it can be related to approximations adopted in MHD simulations to treat optically thick accretion flow within the MAD-zone, or may indicate that accretion disks are geometrically thicker than the standard theory predicts.