Low-mass Active Galactic Nuclei on the Fundamental Plane of Black Hole Activity

TL;DR

This study extends the fundamental plane of black hole activity to low-mass active galactic nuclei by developing a new measurement method, resulting in 19 new sources that support the universality of accretion and jet processes across different black hole masses.

Contribution

The paper introduces a novel method to measure radio flux from VLA FIRST images, significantly increasing the sample of low-mass AGNs on the fundamental plane and supporting the universality of accretion-jet physics.

Findings

Low-mass AGNs follow the standard radio/X-ray correlation.

The universal fundamental plane relation applies to low-mass AGNs.

Radio loudness may depend on both Eddington ratio and black hole mass.

Abstract

It is widely known that in active galactic nuclei (AGNs) and black hole X-ray binaries (BHXBs), there is a tight correlation among their radio luminosity ($L_R$), X-ray luminosity ($L_X$) and BH mass ($\mbh$), the so-called `fundamental plane' (FP) of BH activity. Yet the supporting data are very limited in the $\mbh$ regime between stellar mass (i.e., BHXBs) and 10$^{6.5}$\,\msun\ (namely, the lower bound of supermassive BHs in common AGNs). In this work, we developed a new method to measure the 1.4 GHz flux directly from the images of the VLA FIRST survey, and apply it to the type-1 low-mass AGNs in the \cite{2012ApJ...755..167D} sample. As a result, we obtained 19 new low-mass AGNs for FP research with both \mbh\ estimates ($\mbh \approx 10^{5.5-6.5}$\,\msun), reliable X-ray measurements, and (candidate) radio detections, tripling the number of such candidate sources in the literature.Most (if not all) of the low-mass AGNs follow the standard radio/X-ray correlation and the universal FP relation fitted with the combined dataset of BHXBs and supermassive AGNs by \citet{2009ApJ...706..404G}; the consistency in the radio/X-ray correlation slope among those accretion systems supports the picture that the accretion and ejection (jet) processes are quite similar in all accretion systems of different \mbh. In view of the FP relation, we speculate that the radio loudness $\mathcal{R}$ (i.e., the luminosity ratio of the jet to the accretion disk) of AGNs depends not only on Eddington ratio, but probably also on \mbh.