Exploring X-ray and radio emission of type 1 AGN up to z ~ 2.3
  X-ray emission from AGN is dominated by the accretion disk around a SMBH. The
radio luminosity, however, has not such a clear origin except in the most
powerful sources where jets are evident. The origin (and even the very
existence) of the local bi-modal distribution in radioloudness is also a
debated issue. By analysing X-ray, optical and radio properties of a large
sample of type 1 AGN up to z>2, where the bulk of this population resides, we
aim to explore the interplay between radio and X-ray emission in AGN, in order
to further our knowledge on the origin of radio emission, and its relation to
accretion. We analyse a large (~800 sources) sample of type 1 AGN and QSOs
selected from the 2XMMi X-ray source catalogue, cross-correlated with the SDSS
DR7 spectroscopic catalogue, covering a redshift range from z~0.3 to z~2.3.
SMBH masses are estimated from the Mg II emission line, bolometric luminosities
from the X-ray data, and radio emission or upper limits from the FIRST
catalogue. Most of the sources accrete close to the Eddington limit and the
distribution in radioloudness does not appear to have a bi-modal behaviour. We
confirm that radioloud AGN are also X-ray loud, with an X-ray-to-optical ratio
up to twice that of radioquiet objects, even excluding the most extreme
strongly jetted sources. By analysing complementary radio-selected control
samples, we find evidence that these conclusions are not an effect of the X-ray
selection, but are likely a property of the dominant QSO population. Our
findings are best interpreted in a context where radio emission in AGN, with
the exception of a minority of beamed sources, arises from very close to the
accretion disk and is therefore heavily linked to X-ray emission. We also
speculate that the RL/RQ dichotomy might either be an evolutionary effect that
developed well after the QSO peak epoch, or an effect of incompleteness in
small samples.
