Comparison of radio observations and numerical simulations of the radio lobes of cygnus A

Joel C. Carvalho, Ruth A. Daly, Matthew P. Mory, Christopher P. O'Dea

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

We present a comparison of radio observations of the powerful archetypal radio galaxy Cyg A and two-dimensional numerical hydrodynamic simulations. We characterize some global trends in the observed radio properties and compare them with the properties of a simulated radio source. The observational results are the following. The width of the observed surface brightness distribution perpendicular to the source axis can be well characterized by a Gaussian over most of the length of the source. The ratio of the Gaussian FWHM to the second moment is fairly constant along the source, with an average value of about 2.5, indicating that they give roughly consistent measurements of the source width. The average observed surface brightness, estimated pressure, and estimated minimum-energy B-field decrease with distance from the hot spots. We find evidence for significant structure in the estimated cross-sectional slices of the emissivity. The numerical results are the following. Jets propagating in a constant-density atmosphere decelerate with time. Thus, the estimated dynamical age of the source is greater than the actual age of the source. For a source similar to Cyg A, the difference is 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, 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 two-dimensional simulations give a reasonable representation of the properties of Cyg A.

Original languageEnglish (US)
Pages (from-to)126-144
Number of pages19
JournalAstrophysical Journal
Volume620
Issue number1 I
DOIs
StatePublished - Feb 10 2005

Fingerprint

radio observation
lobes
radio
simulation
brightness
emissivity
moments
brightness distribution
cross section
hydrodynamics
comparison
radio galaxies
atmosphere
energy
trends
atmospheres
cross sections
profiles

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Carvalho, Joel C. ; Daly, Ruth A. ; Mory, Matthew P. ; O'Dea, Christopher P. / Comparison of radio observations and numerical simulations of the radio lobes of cygnus A. In: Astrophysical Journal. 2005 ; Vol. 620, No. 1 I. pp. 126-144.
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Comparison of radio observations and numerical simulations of the radio lobes of cygnus A. / Carvalho, Joel C.; Daly, Ruth A.; Mory, Matthew P.; O'Dea, Christopher P.

In: Astrophysical Journal, Vol. 620, No. 1 I, 10.02.2005, p. 126-144.

Research output: Contribution to journalArticle

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N2 - We present a comparison of radio observations of the powerful archetypal radio galaxy Cyg A and two-dimensional numerical hydrodynamic simulations. We characterize some global trends in the observed radio properties and compare them with the properties of a simulated radio source. The observational results are the following. The width of the observed surface brightness distribution perpendicular to the source axis can be well characterized by a Gaussian over most of the length of the source. The ratio of the Gaussian FWHM to the second moment is fairly constant along the source, with an average value of about 2.5, indicating that they give roughly consistent measurements of the source width. The average observed surface brightness, estimated pressure, and estimated minimum-energy B-field decrease with distance from the hot spots. We find evidence for significant structure in the estimated cross-sectional slices of the emissivity. The numerical results are the following. Jets propagating in a constant-density atmosphere decelerate with time. Thus, the estimated dynamical age of the source is greater than the actual age of the source. For a source similar to Cyg A, the difference is 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, 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 two-dimensional simulations give a reasonable representation of the properties of Cyg A.

AB - We present a comparison of radio observations of the powerful archetypal radio galaxy Cyg A and two-dimensional numerical hydrodynamic simulations. We characterize some global trends in the observed radio properties and compare them with the properties of a simulated radio source. The observational results are the following. The width of the observed surface brightness distribution perpendicular to the source axis can be well characterized by a Gaussian over most of the length of the source. The ratio of the Gaussian FWHM to the second moment is fairly constant along the source, with an average value of about 2.5, indicating that they give roughly consistent measurements of the source width. The average observed surface brightness, estimated pressure, and estimated minimum-energy B-field decrease with distance from the hot spots. We find evidence for significant structure in the estimated cross-sectional slices of the emissivity. The numerical results are the following. Jets propagating in a constant-density atmosphere decelerate with time. Thus, the estimated dynamical age of the source is greater than the actual age of the source. For a source similar to Cyg A, the difference is 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, 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 two-dimensional simulations give a reasonable representation of the properties of Cyg A.

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