The radio-loud AGN population at z>~1 in the COSMOS field. I. Selection
  and Spectral Energy Distributions
  We select a sample of radio galaxies at high redshifts (z>~1) in the COSMOS
field, by cross-matching optical/infrared images with the FIRST radio data. The
aim of this study is to explore the high-z radio-loud (RL) AGN population at
much lower luminosities than the classical samples of distant radio sources and
similar to those of the local population of radio galaxies. The wide
multiwavelength coverage provided by the COSMOS survey allows us to derive
their Spectral Energy Distributions (SEDs). The SED modeling with stellar and
dust components (with our code 2SPD) returns several important quantities
associated with the AGN and host properties. The final sample consists of 74 RL
AGN, which extends the sample previously selected by Chiaberge et al. (2009)
and studied by Baldi et al. (2013). The resulting photometric redshifts range
from z~0.7 to 3. The sample mostly includes compact radio sources, but also 21
FRIIs; the radio power distribution of the sample at 1.4 GHz covers
~10^(31.5)-10^(34.3) \erg\s\Hz. The stellar mass of the hosts ranges
~10^(10)-10^(11.5) M_{sun}. The SEDs are dominated by the contribution from an
old stellar population for most of the sources. UV and mid-IR (MIR) excesses
are observed for half of the sample. The dust luminosities are in the range
L_(dust) ~10^(43)-10^(45.5) erg/s (T ~350-1200 K). UV luminosities at 2000 A
ranges ~10^(41.5)-10^(45.5) erg/s. UV emission is significantly correlated with
both IR and radio luminosities, the former being the stronger link. However,
the origin of UV and dust emission, whether it is produced by the AGN of by
star formation, is still unclear. Our results show that this RL AGN population
at high redshifts displays a wide variety of properties from possible quasars
at the highest luminosities, to low-luminosity old galaxies, similarly to the
local FRI-FRII dichotomy.
