The pc-scale radio structure of MIR-observed radio galaxies

TL;DR

This study explores the connection between accretion processes and jet properties in radio galaxies using VLBA and MIR data, revealing correlations between accretion rates, jet morphology, and core luminosity, and challenging simple morphology-accretion mode associations.

Contribution

It provides a detailed analysis of pc-scale radio structures and their relation to accretion modes in a well-defined sample of radio galaxies, incorporating new VLBA observations and archival data.

Findings

No strict link between FR morphology and accretion mode.

Higher accretion rates tend to produce more extended jets.

Strong correlation between MIR luminosity and VLBA core luminosity.

Abstract

We investigated the relationship between the accretion process and jet properties by ultilizing the VLBA and mid-infrared (MIR) data for a sample of 45 3CRR radio galaxies selected with a flux density at 178 MHz $>16.4$ Jy, 5 GHz VLA core flux density $\geq$ 7 mJy, and MIR observations. The pc-scale radio structure at 5 GHz are presented by using our VLBA observations for 21 sources in February, 2016, the analysis on the archival data for 16 objects, and directly taking the measurements for 8 radio galaxies available in literatures. The accretion mode is constrained from the Eddington ratio with a dividing value of 0.01, which is estimated from the MIR-based bolometric luminosity and the black hole masses. While most FRII radio galaxies have higher Eddington ratio than FRIs, we found that there is indeed no single correspondence between the FR morphology and accretion mode with eight FRIIs at low accretion and two FRIs at high accretion rate. There is a significant correlation between the VLBA core luminosity at 5 GHz and the Eddington ratio. Various morphologies are found in our sample, including core only, single-sided core-jet, and two-sided core-jet structures. We found that the higher accretion rate may be more likely related with the core-jet structure, thus more extended jet. These results imply that the higher accretion rates are likely able to produce more powerful jets. There is a strong correlation between the MIR luminosity at 15 $\mu$m and VLBA 5 GHz core luminosity, in favour of the tight relation between the accretion disk and jets. In our sample, the core brightness temperature ranges from $10^{9}$ to $10^{13.38}$ K with a median value of $10^{11.09}$ K indicating that systematically the beaming effect may not be significant....