Resolving the shocks in radio galaxy nebulae: HST and 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 VLA and 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]λ5007 and [OII]λ3727 line emission using the Linear Ramp Filters on WFPC2. The correlations between the emission line morphology and the [OIII]/[OII] line ratios with the radio emission seen in ground based observations are clarified by the HST imaging. We confirm that the radio lobes and hot-spots are preferentially associated with lower ionization gas. 3C 171 exhibits high surface brightness emission line gas mainly along the radio source axis. The lowest ionization gas is seen at the Eastern hot spot. In 3C 277.3 there is bright high ionization gas (and continuum) offset just to the east of the radio knot K1. Our observations are consistent with previous work suggesting that this emission is produced by precursor gas ionized by the shock being driven into the cloud by the deflected radio jet. In PKS 2250-41 we resolve the emission line arc which wraps around the outer rim of the western lobe. The lower ionization [OII] emission is nested just interior to the higher ionization [OIII] emission suggesting that we have resolved the cooling region behind the bow shock. We also detect possible continuum emission from the secondary hot-spot. Thus, our observations support the hypothesis that in these sources, the interaction between the expanding radio source and the ambient gas strongly influences the morphology, kinematics, and ionization of the gas. Subject headings: galaxies: active — galaxies: jets — shock waves —– galaxies: individual (3C 171, PKS 2250-41, 3C 277.3) —galaxies: interaction —– galaxies: kinematics and dynamics Department of Physics & Astronomy, The Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD21218;tilak@pha.jhu. edu Department of Physics, Rochester Institute of Technology,One LombMemorial Drive, Rochester, NY-14623;odea@cis.rit. edu Department of Physics & Astronomy, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK;C.Tadhunter@sheffield.ac. uk, K.Willis@sheffield.ac. uk Netherlands Foundation for Research in Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands;morganti@astron.nl Center for Imaging Sciences, Rochester Institute of Technology, One Lomb Memorial Drive, Rochester, NY-14623; baum@cis.rit. edu Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218; koekemoe@stsci.edu Dipartimento di Astronomia, via Ranzani 1, I-40127 Bologna, Italy Ist. di Radioastronomia, CNR, Via Gobetti 101, I-40129 Bologna, Italy;ddallaca@ira.cnr. it Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program 6657 (PI C. Tadhunter). Operated by the Association of Universities for Research in Astronomy under contract NAS 5-26555 with the National Aeronautics and Space Administration.