On the Jet Production Efficiency in a Sample of the Youngest Radio Galaxies

Abstract

Here we discuss the jet production efficiency in a sample of 17 young radio galaxies with measured redshifts, kinematic ages, and nuclear X-ray fluxes, for which the observed luminosities of compact jets/lobes and accretion disks correspond to the same episode of the AGN activity. For the targets, we analyze the available optical data, estimating the bolometric luminosities of the accretion disks $L_{\mathrm{bol}}$, and the black hole masses; we also derive the minimum jet kinetic luminosities, $P_{\mathrm{j}}$. With such, we investigate the distribution of our sample in the three-dimensional space of the accretion rate ${\lambda }_{\mathrm{Edd}}\equiv L_{\mathrm{bol}}/L_{\mathrm{Edd}}$, the nuclear X-ray luminosity $L_{\mathrm{X}}$ considered here as a limit for the emission of the disk coronae, and $P_{\mathrm{j}}$, expressing the latter two parameters either in the Eddington units, or in the units of the disk luminosity. We find that (i) the accretion rate ${\lambda }_{\mathrm{Edd}}$ in our sample is distributed within a narrow range ${\lambda }_{\mathrm{Edd}}\sim 0.01-0.2$; (ii) the normalized jet power $P_{\mathrm{j}}/L_{\mathrm{Edd}}$ formally correlates with the accretion rate ${\lambda }_{\mathrm{Edd}}$, with some saturation at the largest values ${\lambda }_{\mathrm{Edd}}>0.05$; (iii) the jet production efficiency ${\eta }_{\mathrm{jet}}\equiv P_{\mathrm{j}}/{\dot{M}}_{\mathrm{acc}}{c}^2$ spans a range from ${\eta }_{\mathrm{jet}}\lesssim 10^{-3}$ up to $\sim 0.2$ at maximum, which is below the level expected for magnetically arrested disks around maximally spinning black holes; and (iv) there is a diversification in ${\eta }_{\mathrm{jet}}$ on the hardness--intensity diagram $L_{\mathrm{X}}/L_{\mathrm{bol}}-{\lambda }_{\mathrm{Edd}}$, with the jets being produced most efficiently during the high/hard states, and suppressed during the soft states.

the Astrophysical Journal, in press