In a dynamical-radiative model we recently developed to describe the physics
of compact, GHz-Peaked-Spectrum (GPS) sources, the relativistic jets propagate
across the inner, kpc-sized region of the host galaxy, while the electron
population of the expanding lobes evolves and emits synchrotron and
inverse-Compton (IC) radiation. Interstellar-medium gas clouds engulfed by the
expanding lobes, and photoionized by the active nucleus, are responsible for
the radio spectral turnover through free-free absorption (FFA) of the
synchrotron photons. The model provides a description of the evolution of the
spectral energy distribution (SED) of GPS sources with their expansion,
predicting significant and complex high-energy emission, from the X-ray to the
gamma-ray frequency domain. Here, we test this model with the broad-band SEDs
of a sample of eleven X-ray emitting GPS galaxies with Compact-Symmetric-Object
(CSO) morphology, and show that: (i) the shape of the radio continuum at
frequencies lower than the spectral turnover is indeed well accounted for by
the FFA mechanism; (ii) the observed X-ray spectra can be interpreted as
non-thermal radiation produced via IC scattering of the local radiation fields
off the lobe particles, providing a viable alternative to the thermal,
accretion-disk dominated scenario. We also show that the relation between the
hydrogen column densities derived from the X-ray (N_H) and radio (N_HI) data of
the sources is suggestive of a positive correlation, which, if confirmed by
future observations, would provide further support to our scenario of
high-energy emitting lobes.Comment: 29 pages, 3 figures, 6 tables; to appear in ApJ. A few clarifications
included, according to referee's suggestion
