The presence of optical synchrotron jets in radio galaxies is relatively rare. Here we show that of the nearest Ðve FR I 3CR radio galaxies showing optical jets, four show evidence for almost circular, presumably face-on, dust disks. This is strong support for the twofold idea that (1) jets emerge close to perpendicular to inner gas disks and (2) optical nonthermal synchrotron emission is seen only when the jet points toward the observer. The implied critical angle to the line of sight is approximately 30¡È40¡; i.e., if the angle of the jet to the line of sight is less than about 40¡ we see an optical jet. The corresponding relativistic c factor is B1.5, which is consistent with current observations of jet proper motion that show a range up to cD6 for M87. The relatively low speeds implied by cB1.5 may be due to a global deceleration of the jet as in uniÐed theories or else to stratiÐcation within the jet. Unresolved nuclei are common in the optical. Their luminosities are also consistent with the beaming concept when compared to inclination inferred from the dust lanes. The disk sizes are typically several hundred parsecs to kiloparsec size. The galaxy with an optical jet that does not show a face-on disk, M87, instead has more complex radial dust and ionized gas Ðlaments (Refer to PDF file for exact formulas).

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Also archived in: arXiv: astro-ph/0007358 v1 24 Jul 2000 Support for this work was provided by NASA through proposal GO-5476.01-93A from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under contract NAS 5-26555.ISSN:1538-4365 Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works in February 2014.

Document Type


Department, Program, or Center

School of Physics and Astronomy (COS)


RIT – Main Campus