A New Radio Loudness Diagnostic for Active Galaxies: a Radio-To-Mid-Infrared Parameter

TL;DR

This paper introduces a new radio-to-mid-infrared diagnostic ratio for active galaxies, enabling better characterization of radio contributions relative to AGN activity without optical limitations.

Contribution

It proposes the 8.4GHz/[O IV] ratio as a novel, effective diagnostic for assessing radio contributions in Seyfert galaxies, independent of optical data.

Findings

Seyfert 1 and Seyfert 2 galaxies have similar radio contributions relative to AGN.

Star formation dominated sources are more radio loud than AGN dominated ones.

Radio contribution correlates with lower mass accretion rates in star formation dominated sources.

Abstract

We have studied the relationship between the nuclear (high-resolution) radio emission, at 8.4 GHz (3.6 cm) and 1.4 GHz (20 cm), the [O IV] 25.89um, [Ne III] 15.56um and [Ne II] 12.81um emission lines and the black hole mass accretion rate for a sample of Seyfert galaxies. In order to characterize the radio contribution for the Seyfert nuclei we used the 8.4GHz/[O IV] ratio, assuming that [O IV] scales with the luminosity of the AGN. From this we find that Seyfert 1's (i.e., Seyfert 1.0's, 1.2's, and 1.5's) and Seyfert 2's (i.e., Seyfert 1.8's, 1.9's, and 2.0's) have similar radio contributions, relative to the AGN. On the other hand, sources in which the [Ne II] emission is dominated either by the AGN or star formation have statistically different radio contributions, with star formation dominated sources more "radio loud", by a factor of ~2.8 on average, than AGN dominated sources. We show that star formation dominated sources with relatively larger radio contribution have smaller mass accretion rates. Overall, we suggest that 8.4GHz/[O IV], or alternatively, 1.4GHz/[O IV] ratios, can be used to characterize the radio contribution, relative to the AGN, without the limitation of previous methods that rely on optical observables.