The isotropic radio background revisited
  We present an extensive analysis on the determination of the isotropic radio
background. We consider six different radio maps, ranging from 22 MHz to 2.3
GHz and covering a large fraction of the sky. The large scale emission is
modeled as a linear combination of an isotropic component plus the Galactic
synchrotron radiation and thermal bremsstrahlung. Point-like and extended
sources are either masked or accounted for by means of a template. We find a
robust estimate of the isotropic radio background, with limited scatter among
different Galactic models. The level of the isotropic background lies
significantly above the contribution obtained by integrating the number counts
of observed extragalactic sources. Since the isotropic component dominates at
high latitudes, thus making the profile of the total emission flat, a Galactic
origin for such excess appears unlikely. We conclude that, unless a systematic
offset is present in the maps, and provided that our current understanding of
the Galactic synchrotron emission is reasonable, extragalactic sources well
below the current experimental threshold seem to account for the majority of
the brightness of the extragalactic radio sky.
