The Properties and Gaseous Environments of Powerful Classical Double Radio Galaxies

The properties of a sample of 31 very powerful classical double radio galaxies with redshifts between zero and 1.8 are studied. The source velocities, beam powers, ambient gas densities, total lifetimes, and total outflow energies are presented and discussed. The rate of growth of each side of each source were obtained using a spectral aging analysis. The beam power and ambient gas density were obtained by applying the strong shock jump conditions to the ends of each side of the source. The total outflow lifetime was obtained by applying the power-law relationship between the beam power and the total source lifetime derived elsewhere for sources of this type, and the total outflow energy was obtained by combining the beam power and the total source lifetime. Composite profiles were constructed by combining results obtained from each side of each source. The composite profiles indicate that the ambient gas density falls with distance from the central engine. The source velocities, beam powers, total lifetimes, and total energies seem to be independent of radio source size. This is consistent with the standard model in which each source grows at a roughly constant rate during which time the central engine puts out a roughly constant beam power. The fact that the total source lifetimes and energies are independent of radio source size indicates that the sources are being sampled at random times during their lifetimes.Comment: 7 pages, 5 figures, to appear in "Extragalactic Jets: Theory and Observation from Radio to Gamma Ray", eds. T. A. Rector and D. S. De Young, ASP conference series, Replaced version has minor textual correction

High-Redshift Radio Galaxies as a Cosmological Tool: Exploration of a Key Assumption and Comparison with Supernova Results

There are many different approaches to using observations to constrain or determine the global cosmological parameters that describe our universe. Methods that rely upon a determination of the coordinate distance to high-redshift sources are particularly useful because they do not involve assumptions about the clustering properties of matter, or the evolution of this clustering. Two of the methods currently being used to determine the coordinate distance to high-redshift sources are the radio galaxy method and the supernova method. These methods are similar in their dependence on the coordinate distance. Here, the radio galaxy method is briefly described and results are presented. One of the underlying assumptions of the method is explored. In addition, the method is compared and contrasted to the supernova method. The constraints imposed on global cosmological parameters by radio galaxies are consistent with those imposed by supernovae. For a universe that is spatially flat with mean mass density $\Omega_m$ in non-relativistic matter and mean mass density 1- $\Omega_m$ in quintessence, radio galaxies alone indicate at 84 % confidence that the expansion of the universe is accelerating at the current epoch. And, independent of whether or not the universe is spatially flat, radio galaxies alone indicate at 95 % confidence that $\Omega_m$ must be less than 0.6 at the current epoch.Comment: 8 page

Improved Constraints on the Acceleration History of the Universe and the Properties of the Dark Energy

We extend and apply a model-independent analysis method developed earlier by Daly & Djorgovski to new samples of supernova standard candles, radio galaxy and cluster standard rulers, and use it to constrain physical properties of the dark energy as functions of redshift. Similar results are obtained for the radio galaxy and supernova data sets. The first and second derivatives of the distance are compared directly with predictions in a standard model based on General Relativity. The good agreement indicates that General Relativity provides an accurate description of the data on look-back time scales of about ten billion years. The first and second derivatives are combined to obtain the acceleration parameter, assuming only the validity of the Robertson-Walker metric, independent of a theory of gravity and of the physical nature of the dark energy. The acceleration of the universe at the current epoch is indicated by the analysis. The effect of non-zero space curvature on q(z) is explored. We solve for the pressure, energy density, equation of state, and potential and kinetic energy of the dark energy as functions of redshift assuming that General Relativity is the correct theory of gravity, and the results indicate that a cosmological constant in a spatially flat universe provides a good description of each of these quantities over the redshift range from zero to about one. We define a new function, the dark energy indicator, in terms of the first and second derivatives of the coordinate distance and show how this can be used to measure deviations of w from -1 and to obtain a new and independent measure of Omega.Comment: 46 pages, submitted for publicatio

A Detailed Study of the Lobes of Eleven Powerful Radio Galaxies

Radio lobes of a sample of eleven very powerful classical double radio galaxies were studied. Each source was rotated so that the symmetry axis of the source was horizontal, and vertical cross-sectional cuts were taken across the source at intervals of one beam size. These were used to study the cross-sectional surface brightness profiles, the width of each slice, radio emissivity as a function of position across each slice, the first and second moments, and the average surface brightness, minimum energy magnetic field strength, and pressure of each slice. A Gaussian provides a good description of the surface brightness profile of cross-sectional slices. The Gaussian FWHM as a function of distance from the hot spot first increases and then decreases with distance from the hot spot. The width as a function of distance from the hot spot is highly symmetric on each side of the source. The radio emissivity is often close to flat across a slice, indicating a roughly constant emissivity and pressure for that slice. Some slices show variations in radio emissivity that indicate an ``edge-peaked'' pressure profile for that slice; these often occur in slices near the local maxima of the bridge width. The emissivity does not exhibit any signature of emission from a jet. The first moment is generally quite close to zero indicating only small excursions of the ridge line from the symmetry axis of the source. The second moment indicates the same source shape as is found using the Gaussian FWHM. The average magnetic field strength and pressure decrease with increasing distance from the hot spot, reaching a roughly constant value at a location that is typically just before the location of a local maximum of the bridge width. These results are interpreted in terms of a heuristic model for the radio lobes.Comment: 102 pages, 136 figures, accepted for publication in ApJ Supplement Serie

Cosmological Studies with Radio Galaxies and Supernovae

Physical sizes of extended radio galaxies can be employed as a cosmological "standard ruler", using a previously developed method. Eleven new radio galaxies are added to our previous sample of nineteen sources, forming a sample of thirty objects with redshifts between 0 and 1.8. This sample of radio galaxies are used to obtain the best fit cosmological parameters in a quintessence model in a spatially flat universe, a cosmological constant model that allows for non-zero space curvature, and a rolling scalar field model in a spatially flat universe. Results obtained with radio galaxies are compared with those obtained with different supernova samples, and with combined radio galaxy and supernova samples. Results obtained with different samples are consistent, suggesting that neither method is seriously affected by systematic errors. Best fit radio galaxy and supernovae model parameters determined in the different cosmological models are nearly identical, and are used to determine dimensionless coordinate distances to supernovae and radio galaxies, and distance moduli to the radio galaxies. The distance moduli to the radio galaxies can be combined with supernovae samples to increase the number of sources, particularly high-redshift sources, in the samples. The constraints obtained here with the combined radio galaxy plus supernovae data set in the rolling scalar field model are quite strong. The best fit parameter values suggest a value of omega is less than about 0.35, and the model parameter alpha is close to zero; that is, a cosmological constant provides a good description of the data. We also obtain new constraints on the physics of engines that power the large-scale radio emission.Comment: 32 pages. Accepted for publication in the Astrophysical Journa

Comparison of Radio Observations and Numerical Simulations of the Radio Lobes of Cygnus A

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.Comment: the larger figures are available as gif

Radio Galaxy Redshift-Angular Size Data Constraints on Dark Energy

We use FRIIb radio galaxy redshift-angular size data to constrain cosmological parameters in a dark energy scalar field model. The derived constraints are consistent with but weaker than those determined using Type Ia supernova redshift-magnitude data. Subject headings: cosmology: cosmological parameters—cosmology: observation—largescale structure of the universe 1