Nowhere to Hide: Radio-faint AGN in the GOODS-N field. II.
  Multi-wavelength AGN selection techniques and host galaxy properties
  Obtaining a census of active galactic nuclei (AGN) activity across cosmic
time is critical to our understanding of galaxy evolution and formation. Many
AGN classification techniques are compromised by dust obscuration. However,
very long baseline interferometry (VLBI) can be used to identify compact
emission that can only be attributed to AGN activity.
  This is the second in a series of papers dealing with the compact radio
population in the GOODS-N field. We review 14 different AGN classification
techniques in the context of a VLBI-detected sample, and use these to
investigate the nature of the AGN as well as their host galaxies.
  We find that no single identification technique can identify all VLBI objects
as AGN. Infrared colour-colour selection is most notably incomplete. However,
the usage of multiple classification schemes can identify all VLBI-selected
AGN, independently verifying similar approaches used in other deep field
surveys. In the era of large area surveys with instruments such as the SKA and
ngVLA, multi-wavelength coverage, which relies heavily upon observations from
space, is often unavailable. Therefore, VLBI remains an integral component in
detecting AGN of the jetted efficient and inefficient accretion types. A
substantial fraction (46%) of the VLBI AGN have no X-ray counterpart, which is
most likely due to lack of sensitivity in the X-ray band. A high fraction of
the VLBI AGN reside in low or intermediate redshift dust-poor early-type
galaxies. These most likely exhibit inefficient accretion. Finally, a
significant fraction of the VLBI AGN reside in symbiotic dusty starburst - AGN
systems. We present an extensive compilation of the multi-wavelength properties
of all the VLBI-selected AGN in GOODS-N in the Appendix.
