# The Kinetically Dominated Quasar 3C~418

## TL;DR

This paper identifies 3C 418 as one of the most kinetically dominated quasars, with jet power exceeding the thermal luminosity of its accretion flow, supporting magnetically arrested accretion models.

## Contribution

It provides detailed measurements of jet power and accretion luminosity in 3C 418, demonstrating extreme kinetic dominance and supporting magnetic flux saturation models.

## Key findings

- 3C 418's jet power exceeds its bolometric luminosity by a factor of about 4.8.
- The jet power is approximately 57% of the Eddington luminosity.
- Results support magnetically arrested accretion models with maximum magnetic flux saturation.

## Abstract

The existence of quasars that are kinetically dominated, where the jet kinetic luminosity, $Q$, is larger than the total (IR to X-ray) thermal luminosity of the accretion flow, $L_{\rm{bol}}$, provides a strong constraint on the fundamental physics of relativistic jet formation. Since quasars have high values of $L_{\rm{bol}}$ by definition, only $\sim 10$ kinetically dominated quasars (with $\overline{Q}/L_{\rm{bol}}>1$) have been found, where $\overline{Q}$ is the long term time averaged jet power. We use low frequency (151 MHz$-$1.66 GHz) observations of the quasar 3C\,418 to determine $\overline{Q}\approx 5.5 \pm 1.3 \times 10^{46} \rm{ergs~s^{-1}}$. Analysis of the rest frame ultraviolet spectrum indicates that this equates to $0.57 \pm 0.28$ times the Eddington luminosity of the central supermassive black hole and $\overline{Q}/L_{\rm{bol}} \approx 4.8 \pm 3.1$, making 3C\,418 one of the most kinetically dominated quasars found to date. It is shown that this maximal $\overline{Q}/L_{\rm{bol}}$ is consistent with models of magnetically arrested accretion of jet production in which the jet production reproduces the observed trend of a decrement in the extreme ultraviolet continuum as the jet power increases. This maximal condition corresponds to an almost complete saturation of the inner accretion flow with vertical large scale magnetic flux (maximum saturation).