Research in Astron. and astroph., 18, 108-108 (2018/September-0)
The pc-scale radio structure of MIR-observed radio galaxies.
YUAN Y., GU M.-F. and CHEN Y.-J.
Abstract (from CDS):
We investigated the relationship between the accretion process and jet properties by utilizing very long baseline array (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 very large array (VLA) core flux density >=7 mJy and MIR observations. The pc-scale radio structure at 5 GHz is presented by using our VLBA observations for 21 sources acquired in February, 2016, the analysis of archival data for 16 objects and directly obtaining measurements for eight radio galaxies available from 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 Fanaroff-Riley type II radio galaxies (FRIIs) have higher Eddington ratio than Fanaroff-Riley type I radio galaxies (FRIs), we found that there is indeed no single correspondence between the FR morphology and accretion mode with eight FRIIs at low accretion rate 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 identified 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 generating a 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 µm and VLBA 5 GHz core luminosity, in favor of the tight relation between the accretion disk and jets. In our sample, the core brightness temperature ranges from 109 to 1013.38 K with a median value of 1011.09 K, indicating that systematically the beaming effect may not be significant. The exceptional cases, FRIs at high accretion rates and FRIIs at low accretion rates, are exclusively at the high and low ends, respectively, of the distribution of the flux ratio for VLBA core to 178 MHz flux density. It is not impossible that the locations of these sources are due to the recent shining or weakening of their central engines (i.e., both accretion and jet).
galaxies: active - galaxies: structure - galaxies: general - radio continuum: galaxies
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