We present a comparison of radio observations of the archetypal powerful radio galaxy Cygnus A and 2-D numerical hydrodynamical simulations. We characterize some global trends in the observed radio properties and compare them with the properties of a simulated radio source. The numerical results are the following. Jets propagating in a constant density atmosphere will decelerate with time. Thus, the estimated dynamical age of the source will be greater than the actual age of the source. For a source similar to Cygnus A the difference will be about a factor of 2. The second moment gives an accurate representation of the "true" width of the simulated source. The Gaussian FWHM tends to be about 40% larger than the true width and can be systematically in error if the surface brightness exhibits multiple peaks. We suggest that the ratio of the Gaussian FWHM to the second moment may be a diagnostic of the emissivity profile in the lobes. The simulations can qualitatively reproduce the overall observed morphology and the behavior of the cross-sections in surface brightness, the decline in surface brightness with distance from the hot spots, and the width of the lobes. This suggests that the 2-D simulations give a reasonable representation of the properties of Cygnus A.

Publication Date



This is the pre-print of an article published by the American Astronomical Society. The final, published version is available here: https://doi.org/10.1086/426857

© 2005 The American Astronomical Society

Also archived in: arXiv:astro-ph/0406212 v2 19 Oct 2004

JCC acknowledges the financial support of PRONEX/Finep and CNPq and the hospitality of STScI where this work was carried out. This work was supported in part by a grant to C. O’Dea from the Space Telescope Science Institute [STScI] Collaborative Visitor Program which funded visits by JCC to STScI, and by grant AST-0206002 to R. Daly from the U. S. National Science Foundation.

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Document Type


Department, Program, or Center

School of Physics and Astronomy (COS)


RIT – Main Campus