A strong negative correlation between radio loudness $R_{\mathrm{UV}}$ and optical-to-X-ray spectral index ${\alpha }_{\mathrm{ox}}$ in low-luminosity AGNs

Abstract

It has been argued for years that the accretion mode changes from bright active galactic nuclei (AGNs) to low-luminosity AGNs (LLAGNs) at a rough dividing point of bolometric Eddington ratio $\lambda \sim 10^{-2}$. In this work, we strengthen this scenario through investigation of the relationship between the radio loudness $R_{\mathrm{UV}}$ and the optical-to-X-ray spectral index ${\alpha }_{\mathrm{ox}}$ in LLAGNs with $10^{-6}\lesssim \lambda \lesssim 10^{-3}$. We compile from literature a sample of 32 LLAGNs, consisting 18 LINERs and 14 low Eddington ratio Seyfert galaxies, and observe a strong negative $R_{\mathrm{UV}}$--${\alpha }_{\mathrm{ox}}$ relationship, with large scatter in both $R_{\mathrm{UV}}$ and ${\alpha }_{\mathrm{ox}}$. We further demonstrate that this negative correlation, and the additional two negative relationships reported in literature ($R_{\mathrm{UV}}$--$\lambda$ and ${\alpha }_{\mathrm{ox}}$--$\lambda$ correlations), can be understood consistently and comprehensively under the truncated accretion--jet model, the model that has been applied successfully applied to LLAGNs. We argue that the scatter in the observations are (mainly) due to the spread in the viscosity parameter $\alpha$ of a hot accretion flow, a parameter that potentially can serve as a diagnose of the strength and/or configuration of magnetic fields in accretion flows.

8 pages, 3 figures, 2 tables. Accepted by MNRAS

References in corpus (15)

• Modelling the behaviour of accretion flows in X-ray binaries
• Radio-Loudness of Active Galactic Nuclei: Observational Facts and Theoretical Implications
• The power of relativistic jets is larger than the luminosity of their accretion disks
• Radiatively Inefficient Accretion in Nearby Galaxies
• Numerical Simulation of Hot Accretion Flows (III): Revisiting wind properties using trajectory approach
• Global simulations of axisymmetric radiative black hole accretion disks in general relativity with a sub-grid magnetic dynamo
• Correlation between the photon index and X-ray luminosity of black hole X-ray binaries and active galactic nuclei: observations and interpretation
• Low-Luminosity Active Galactic Nuclei: Are They UV-Faint and Radio Loud?
• Revisiting the "Fundamental Plane" of Black Hole Activity at Extremely Low Luminosities
• On the origin of X-ray emission in some FR Is: ADAF or jet?
• Empirical relation between angular momentum transport and thermal-to-magnetic pressure ratio in shearing box simulations
• On the origin of the hard X-Ray excess of high-synchrotron-peaked BL Lac object Mrk 421
• Fundamental Plane of Black Hole Activity in Quiescent Regime
• A luminous hot accretion flow in the low-luminosity active galactic nucleus NGC 7213
• A toy model for X-ray spectral variability of active galactic nuclei

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• Evaluating quenching in cosmological simulations of galaxy formation with spectral covariance in the optical window