RADIO, OPTICAL AND X-RAY OBSERVATIONS OF PKS-2250-41 - A JET GALAXY COLLISION/

New optical, radio and X-ray observations are used to investigate the morphology, ionization and kinematics of extended structures in the ho st galaxy of the radio source PKS 2250 - 41 (z=0.308). The data provid e clear evidence for a powerful interaction between the radio jets and the ambient interstellar medium. Not only do [O III] emission-line im ages show spectacular extended are structures associated with the radi o lobes on both sides of the galaxy nucleus on a scale of 40-65 kpc,(1 ) but there is also large depolarization in the western radio lobe at the position of the western emission-line are. Optical long-slit spect ra of the extended emission-line regions provide the first convincing evidence that the radio jets can have a major ionizing effect on the w arm gas in powerful radio galaxies: while the low-ionization [N II] an d [S II] lines are broad (FWHM similar to 300-500 km s(-1)) across the entire emission-line nebulosity, the higher ionization [O III] lines are significantly narrower in the western emission-line arc (FWHM = 24 0 +/- 10 km s(-1)). This anticorrelation between Linewidth and ionizat ion is difficult to explain in terms of central source photoionization , but is entirely consistent with the compression or direct ionization effects of fast shocks driven by the radio jets. Further evidence for shocks is provided by the minimum in the ionization state at the posi tion of the radio lobes, and by [O III](5007 + 4959)/4300 and He II/H beta diagnostic ratios which are more consistent with shocks than with photoionization. The spectacular nature of the jet/cloud interaction in this object is best explained in terms of a direct collision betwee n the radio jet and a companion galaxy in the surrounding group. This model is supported by the detection of a blue continuum source in the western are with a colour and luminosity characteristic of late-type s piral galaxies.