The fingerprints of Photoionization and Shock-Ionization in two CSS
  sources
  We investigate the ionization state of the Extended Emission-Line Regions
(EELRs) around two compact steep-spectrum (CSS) radio galaxies, 3C~268.3 and
3C~303.1, in order to identify the contribution of photoionization and
shock-ionization. We perform a new spectroscopical (long-slit) analysis with
GMOS/Gemini with the slit oriented in the radio-jet direction, where outflows
are known to exist. The [Ne V]$\lambda 3426$ emission is the most interesting
feature of the spectra and the key to breaking the degeneracy between the
models: since this emission-line is more extended than HeII, it challenges the
ionization structure proposed by any photoionization model, also its intensity
relative to H$\beta$ does not behave as expected with respect to the ionization
parameter U in the same scenario. On the contrary, when it is compared to the
intensity of [OII]$\lambda3727$/H$\beta$ and all these results are joined, the
whole scenario is plausible to be explained as emission coming from the hot,
compressed, shocked gas in shock-ionization models. Although the model fitting
is strongly sensitive to the chosen line-ratios, it argues for the presence of
external and strong ionizing fields, such as the precursor field created by the
shock or/and the AGN radiation field. In this paper, we show how AGN
photoionization and shock-ionization triggered by jet-cloud interaction work
together in these EELRs in order to explain the observed trends and line-ratio
behaviours in a kinematically acceptable way.
