Contatto di riferimento: Marcello Giroletti
Partecipanti: Dr. Marco Chiaberge (IRA&STSCI)
Abstract: Radio-loud AGNs are invariably associated with the most massive galaxies and the most massive black holes.
The origin of their relativistic jets is still an open issue. While we still don’t know the details of the physics of jet launching, we recently achieved important information from observations of a large number of these objects.
In this talk, I will focus on results from our HST studies of radio galaxies from z~0 to z~2.5.
In an attempt to investigate the role of mergers in triggering these AGNs, we measured the merger fraction of Type 2 radio-loud and radio-quiet active galactic nuclei at z>1 using new samples.
The full sample spans an unprecedented range in both redshift and AGN luminosity. We performed statistical tests to determine whether the different samples are differently associated with mergers.
We find that (almost) all radio-loud galaxies at z>1 are clearly associated with recent or ongoing merger events. This is independent of the AGN power. The same properties are seen at lower redshifts.
Conversely, the merger fraction for samples of radio-quiet objects at z>1 is indistinguishable from that of non-active galaxies in the same redshift range. This is strong evidence that mergers are the ultimate triggering mechanism for the radio-loud AGN phenomenon. I will discuss a possible scenario that may account for the origin of jets in the framework of our new results.