The Herschel view of the environment of the radio galaxy 4C+41.17 at z =
  3.8
  We present Herschel observations at 70, 160, 250, 350 and 500 micron of the
environment of the radio galaxy 4C+41.17 at z = 3.792. About 65% of the
extracted sources are securely identified with mid-IR sources observed with the
Spitzer Space Telescope at 3.6, 4.5, 5.8, 8 and 24 micron. We derive simple
photometric redshifts, also including existing 850 micron and 1200 micron data,
using templates of AGN, starburst-dominated systems and evolved stellar
populations. We find that most of the Herschel sources are foreground to the
radio galaxy and therefore do not belong to a structure associated with
4C+41.17. We do, however, find that the SED of the closest (~ 25" offset)
source to the radio galaxy is fully consistent with being at the same redshift
as 4C+41.17. We show that finding such a bright source that close to the radio
galaxy at the same redshift is a very unlikely event, making the environment of
4C+41.17 a special case. We demonstrate that multi-wavelength data, in
particular on the Rayleigh-Jeans side of the spectral energy distribution,
allow us to confirm or rule out the presence of protocluster candidates that
were previously selected by single wavelength data sets.
