  Massive outflows are known to exist, in the form of extended emission-line
regions (EELRs), around about one-third of powerful FR II radio sources. We
investigate the origin of these EELRs by studying the emission-line regions
around compact-steep-spectrum (CSS) radio galaxies that are younger (10$^3$ to
10$^5$ years old) versions of the FR II radio galaxies. We have searched for
and analyzed the emission-line regions around 11 CSS sources by taking integral
field spectra using GMOS on Gemini North. We fit the [\ion{O}{3}] $\lambda
5007$ line and present the velocity maps for each detected emission-line
region. We find, in most cases, that the emission-line regions have
multi-component velocity structures with different velocity dispersions and/or
flux distributions for each component. The velocity gradients of the
emission-line gas are mostly well aligned with the radio axis, suggesting a
direct causal link between the outflowing gas and the radio jets. The complex
velocity structure may be a result of different driving mechanisms related to
the onset of the radio jets. We also present the results from the line-ratio
diagnostics we used to analyze the ionization mechanism of the extended gas,
which supports the scenario where the emission-line regions are ionized by a
combination of AGN radiation and shock excitation.
