  We are currently exploiting the deep radio/optical/IR information available
for the extra-galactic component of the Spitzer First Look Survey (FLS) to
investigate the physical properties of faint radio-selected AGNs, with the aim
of studying the AGN component of sub-mJy radio fields. One of the key
unresolved issues is whether, as a function of cosmic epoch, low-power AGNs are
more related to efficiently accreting systems (mostly radio-quiet) or to
systems with very low accretion rates (mostly radio-loud). Here we present a
sample of optically identified radio-emitting AGNs extracted from the FLS.
Preliminary results show that at the flux densities probed by the FLS (S(1.4
GHz)> 100 microJy) we still have a significant number of radio-loud AGNs,
similarly to what found in 'brighter' sub-mJy radio samples. Very
interestingly, however, we have also a clear and direct evidence of a
population of radio-emitting AGNs in the FLS, whose properties are consistent
with those expected from existing radio-quiet AGN modeling. Such AGNs could be
recognised as such thanks to the availability of IR colors which proved to be
especially useful to efficiently separate radio sources triggered by AGNs, from
sources triggered by star-formation. This latter result supports the idea that
radio-quiet AGNs are not necessarily radio silent, and very promisingly may
indicate that the bulk of the radio-quiet AGN population could emerge from
studies of deeper radio samples.

Cosmology and Nongalactic Astrophysics