|Description:|| High-redshift active galactic nuclei (AGN) provide valuable insight into the early phase of structure formation, black hole growth, and naturally to the evolution of AGN themselves. Radio-loud AGN, which are roughly 10% of the AGN population, additionally can also be used to trace the interactions between the jets and the surrounding material, and the feedback to the host galaxy. Radio-loud AGN with jets pointing at small angle to the line of sight, blazars, can be detected at large cosmological distances as their emission is boosted via relativistic effects. Currently, the highest redshift radio-loud AGN are detected above redshift 6. |
Whether the radio emission originates from a relativistically boosted jet, or a more extended structure around the active galaxy can be inferred from the AGN spectral energy distribution or determined directly mapping the radio morphology with very long baseline interferometry technique. In my talk, I will discuss a few cases of z>4 radio-loud AGN where these two methods provide contradictory results.
The image shows Enhanced Multi Element Remotely Linked Interferometer Network (e-MERLIN) images of the radio-loud AGN J2220+0025 located at z=4.21 (Gabányi et al. 2018).
The details of the 1.5-GHz image: peak intensity 18.2 mJy/beam, lowest positive contour level is drawn at 0.3 mJy/beam further contour levels increase by a factor of 2. The beamsize is 0.41 as x 0.14 as at 28 degree.
The details of the 5-GHz images: peak intensity 4.1 mJy/beam, lowest positive contour level is drawn at 0.13 mJy/beam further contour levels increase by a factor of 2. The beamsize is 0.14 as x 0.33 as at 22 degree.
The white cross at the 5 GHz image marks the position of the single compact feature detected by the European VLBI Network observation at 5 GHz (Cao et al. 2017).