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Date and Time of the Query: 2019-06-20 T09:49:40 PDT
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For refcode 2002A&A...383..104C:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
2002A&A...383..104C The HST survey of the B2 sample of radio-galaxies: Optical nuclei and the FR I/BL Lac unified scheme A. Capetti, A. Celotti, M. Chiaberge, H. R. de Ruiter, R. Fanti, R. Morganti and P. Parma Osservatorio Astronomico di Torino, Strada Osservatorio 20, 10025 Pino Torinese, Italy SISSA/ISAS, Via Beirut 2-4, 34014 Trieste, Italy Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA Osservatorio Astronomico di Bologna, Via Ranzani, 1, 40127 Bologna, Italy Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy Dipartimento di Fisica dell'Universita di Bologna, Via Irnerio 46, 40126 Bologna, Italy Netherlands Foundation for Research in Astronomy, Postbus 2, 7990 AA, Dwingeloo, The Netherlands Received 4 October 2001/Accepted 3 December 2001 Abstract. We examine the optical properties of the nuclei of low luminosity radio-galaxies using snapshot HST images of the B2 sample. In agreement with the results obtained from the analysis of the brighter 3C/FR I sample, we find a correlation between fluxes (and luminosities) of the optical and radio cores. This provides further support for the interpretation that the optical nuclear emission in FR I is dominated by synchrotron emission and that accretion in these sources takes place in a low efficiency radiative regime. In the framework of the FR I/BL Lacs unified scheme, we find that the luminosity difference between FR I and BL Lac nuclei can be reproduced with a common beaming factor in both the radio and the optical band, independent of the extended radio luminosity, thus supporting such a scenario. The corresponding bulk Lorentz factor is significantly smaller than is expected from observational and theoretical considerations in BL Lacs: this can be interpreted as due to a velocity structure in the jet, with a fast spine surrounded by a slower layer. Key words: galaxies: active - galaxies: elliptical and lenticular, cD - galaxies: jets - galaxies: nuclei
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