  Compact Symmetric Objects (CSOs) show radio features such as jets, lobes, hot
spots that are contained within the central 1 kpc region of their host galaxy.
Thus, they are thought to be among the progenitors of large-scale radio
galaxies. A debate on whether the CSOs are compact primarily because they are
young or because they are surrounded by a dense medium impacting their
expansion is ongoing. Until now, attempts to discriminate between the
environmental and genuine youthfulness scenarios have been inconclusive. We
present a study of three CSOs selected on the basis of their puzzling X-ray
absorbing properties in prior Beppo-SAX and/or Chandra X-ray Observatory data.
Our new XMM-Newton observations unambiguously confirm the nature of their X-ray
absorbers. Furthermore, for the first time, our X-ray data reveal the existence
of a population of CSOs with intrinsic hydrogen column density $N_H > 10^{23}$
cm$^{-2}$ that is different from the population of X-ray unabsorbed CSOs. The
two groups appear to be separated in the linear size vs. radio power plane.
This finding suggests that a dense medium in X-ray obscured CSOs may be able to
confine the radio jets. Alternatively, X-ray obscured CSOs could be seen as
radio brighter than their unobscured counterparts either because they reside in
a dense environment or because they have larger jet powers. Our results help
constrain the origin of the X-ray emission and the location and size of the
X-ray obscurer in CSOs, and indicate that the environment may play a key role
during the initial expansion of a radio source.

High Energy Astrophysical Phenomena