  Extended X-ray structures are common in Active Galactic Nuclei (AGNs). Here
we present the first case of a Compact Steep Spectrum (CSS) radio galaxy, 3C
305, in which the X-ray radiation appears to be associated with the optical
emission line region, dominated by the [O III]5007. On the basis of a
morphological study, performed using the comparison between the X-rays, the
optical and the radio band, we argue that the high energy emission has a
thermal nature and it is not directly linked to the radio jet and hotspots of
this source. Finally, we discuss the origin of the extended X-ray structure
connected with the optical emission line region following two different
interpretations: as due to the interaction between matter outflows and
shock-heated environment gas, or as due to gas photoionized by nuclear
emission.
