Resolving the Shocks in Radio Galaxy Nebulae:Hubble Space Telescopeand Radio Imaging of 3C 171, 3C 277.3, and PKS 2250-41

We present the results of HST/WFPC2 medium and narrow band imaging and VLAand MERLIN2 radio imaging of three powerful radio galaxies: 3C 171, 3C 277.3,and PKS 2250-41. We obtained images of the rest frame [OIII]$\lambda$5007 and[OII]$\lambda$3727 line emission using the Linear Ramp Filters on WFPC2. Thecorrelations between the emission line morphology and the [OIII]/[OII] lineratios with the radio emission seen in ground based observations are clarifiedby the HST imaging. We confirm that the radio lobes and hot-spots arepreferentially associated with lower ionization gas. 3C 171 exhibits highsurface brightness emission line gas mainly along the radio source axis. Thelowest ionization gas is seen at the Eastern hot spot. In 3C 277.3 there isbright high ionization gas (and continuum) offset just to the east of the radioknot K1. Our observations are consistent with previous work suggesting thatthis emission is produced by precursor gas ionized by the shock being driveninto the cloud by the deflected radio jet. In PKS 2250-41 we resolve theemission line arc which wraps around the outer rim of the western lobe. Thelower ionization [OII] emission is nested just interior to the higherionization [OIII] emission suggesting that we have resolved the cooling regionbehind the bow shock. We also detect possible continuum emission from thesecondary hot-spot. Thus, our observations support the hypothesis that in thesesources, the interaction between the expanding radio source and the ambient gasstrongly influences the morphology, kinematics, and ionization of the gas.Comment: 27 pages, includes 12 figures and 6 tables, accepted for publication in The Astronomical Journa