Jet Emission in Young Radio Sources: a Fermi-LAT Gamma-ray View
  We investigate the contribution of the beamed jet component to the high
energy emission in young and compact extragalactic radio sources, focusing for
the first time on the gamma-ray band. We derive predictions on the gamma-ray
luminosities associated with the relativistic jet assuming a leptonic radiative
model. The high energy emission is produced via Compton scattering by the
relativistic electrons in a spherical region at the considered scales
($\lesssim$10 kpc). Simulations show a wide range of gamma-ray luminosities,
with intensities up to $\sim10^{46}-10^{48}$ erg s$^{-1}$ depending on the
assumed jet parameters. We find a highly linear relation between the simulated
X-ray and gamma-ray luminosities that can be used to select candidates for a
gamma-ray detection. We compare the simulated luminosity distributions in the
radio, X-ray and gamma-ray regimes with observations for the largest sample of
X-ray detected young radio quasars. Our analysis of $\sim$4-year Fermi Large
Area Telescope (LAT) data does not give any statistically significant
detection. However, the majority of the model-predicted gamma-ray fluxes for
the sample are near or below the current Fermi-LAT flux threshold and
compatible with the derived upper limits. Our study gives constraints on the
minimum jet power ($L_{jet,kin}/L_{disk}>0.01$), on a potential jet
contribution to the X-ray emission in the most compact sources ($\lesssim1$
kpc) and on the particles to magnetic field energy density ratio in broad
agreement with equipartition assumption.
