Mutual distance dependence drives the observed jet power - radio luminosity scaling relations in radio galaxies

TL;DR

This study reveals that the previously observed correlation between jet power and radio luminosity in radio galaxies is largely influenced by distance effects, leading to a much weaker intrinsic relationship than previously thought.

Contribution

The paper demonstrates that the jet power-radio luminosity scaling relations are significantly affected by distance, and provides revised, flatter slopes after accounting for this confounding variable.

Findings

Weak intrinsic correlation between jet power and radio luminosity after distance correction

Previously reported slopes overestimate the true relationship due to distance bias

Different dynamics in FRI and FRII radio galaxies lead to different scaling slopes

Abstract

The kinetic power of radio jets is a quantity of fundamental importance to studies of the AGN feedback process and radio galaxy physics. A widely used proxy for jet power is the extended radio luminosity. A number of empirical methods have been used to calibrate a scaling relationship between jet power (Q) and radio luminosity (L) of the form log(Q) = beta_L * log(L) + C. The regression slope has typically been found to be beta_L ~ 0.7 - 0.8. Here we show that the previously reported scaling relations are strongly affected by the confounding variable, distance. We find that in a sample of FRI X-ray cavity systems, after accounting for the mutual distance dependence, the jet power and radio luminosity are only weakly correlated, with slope beta_L ~ 0.3: significantly flatter than previously reported. We also find that in previously used samples of high-power sources, no evidence for an intrinsic correlation is present when the effect of distance is accounted for. Using a simple model we show that beta_L is expected to be significantly lower in samples of FRI radio galaxies than it is for FRIIs, due to the differing dynamics for these two classes of radio source. For FRI X-ray cavity systems the model predicts beta_L (FRI) ~ 0.5 in contrast to FRII radio galaxies, for which beta_L(FRII) ~ 0.8. We discuss the implications of our finding for studies of radio mode feedback, and radio galaxy physics.