The fundamental plane of black hole activity for low-luminosity radio active galactic nuclei across 1 < z < 4

TL;DR

This study investigates how the fundamental plane of black hole activity varies with properties like radio loudness, Eddington ratio, and star formation in low-luminosity AGNs across a broad redshift range, revealing dependence on radio loudness and accretion rate.

Contribution

It demonstrates that the black hole fundamental plane depends on radio loudness and Eddington ratio, but not on redshift, and explores differences between radio-quiet and radio-loud AGNs.

Findings

BHFP differs between RQ and RL AGNs.

BHFP depends on Eddington ratio for both RQ and RL AGNs.

X-ray emission origins vary with accretion rate and radio loudness.

Abstract

The fundamental plane of black hole activity (BHFP) describes the correlation between radio luminosity ($L_R$), X-ray luminosity ($L_X$), and black hole mass. It reflects a disc-jet connection. However, dependence of BHFP on various physical properties of active galactic nuclei (AGNs) and host galaxies is unclear, especially for low-luminosity AGNs, which is important for understanding accretion physics in AGNs. Here we explore the dependence of BHFP on radio loudness, Eddington ratio ($\lambda_E$), redshift, and galaxy star formation properties at 0.1 < z < 4 for radio AGNs. Based on current deep and large surveys, our studies extend to low luminosities and high redshifts. From GOODS and COSMOS fields, we constructed a homogeneous radio AGN sample including 208 objects. We divided the radio AGN sample into 141 radio-quiet (RQ) AGNs and 67 radio-loud (RL) AGNs according to the radio loudness defined by the $L_R$-to-$L_X$ ratio. This ratio shows a bimodal distribution that is well described by two Gaussian models. Their cross point corresponds to a radio loudness threshold of $\log (L_R/L_X) = -2.73$. RQ and RL AGNs show different BHFPs, indicating a dependence of BHFP on the radio loudness. For both RQ and RL AGNs, BHFP shows a dependence on $\lambda_E$, but no dependence on redshift. BHFP shows a dependence on the galaxy star formation properties for RQ AGNs, while for RL AGNs this dependence disappears. BHFP sheds important light on the accretion physics and X-ray emission origins. X-ray emission of RQ AGNs originates from a combination of advection-dominated accretion flow (ADAF) and synchrotron radiation from jet at $0.01 < \lambda_E < 0.1$, and from jet at $0.1 < \lambda_E < 1$. X-ray emission in RL AGNs originates from a combination of ADAF and jet at $\lambda_E < 0.01$, from jet at $0.01 < \lambda_E < 0.1$, and from a combination of standard thin disc and jet at $\lambda_E > 0.1$.