SIMBAD references

A correlation among the radio luminosity (L_R), X-ray luminosity (L_X), and black hole (BH) mass (M_BH) in active galactic nuclei (AGNs) and BH binaries is known to exist and is called the "fundamental plane" of BH activity. Yuan & Cui predict that the radio/X-ray correlation index, ξ_X, changes from ξ_X~0.6 to ξ_X~1.2–1.3 when L_X/L_Edd decreases below a critical value of ∼10^–6. While many works favor such a change, there are also several works claiming the opposite. In this paper, we gather from the literature the largest quiescent AGN (defined as L_X/L_Edd 10^–6) sample to date, consisting of 75 sources. We find that these quiescent AGNs follow a ξ_X~1.23 radio/X-ray relationship, in excellent agreement with the Yuan & Cui prediction. The reason for the discrepancy between the present result and some previous works is that their samples contain not only quiescent sources but also "normal" ones (i.e., L_X/L_Edd 10^–6). In this case, the quiescent sources will mix up with those normal ones in L_R and L_X. The value of ξ_X will then be between 0.6 and ∼1.3, with the exact value being determined by the sample composition, i.e., the fraction of the quiescent and normal sources. Based on this result, we propose that a more physical way to study the fundamental plane is to replace L_R and L_X with L_R/L_Edd and L_X/L_Edd, respectively.