Astronomy and Astrophysics – Astrophysics
Scientific paper
2001-12-06
Astronomy and Astrophysics
Astrophysics
8 pages, 8 figures, 1 table, to be published in A&A
Scientific paper
10.1051/0004-6361:20011714
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/FRI 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 FRI is dominated by synchrotron emission and that accretion in these sources takes place in a low efficiency radiative regime. In the framework of the FRI/BL Lacs unified scheme, we find that the luminosity difference between FRI 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.
Capetti Alessandro
Celotti Annalisa
Chiaberge Marco
de Ruiter Hans R.
Fanti Roberto
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