arXiv subjects

Ruth A. Daly

Publications and source records attributed to Ruth A. Daly.

39 records · Page 3Linked to original sources

arXiv1995

Lateral Expansion of the Bridges of Cygnus A and other Powerful Radio Sources

Measurements of the width of the radio bridge at several locations along the bridge for each of four powerful extended radio sources are presented. Adopting a few simple assumptions, these measurements may be used to predict the radio surface brightness as a function of position across the radio bridge. The predicted and observed surface brightnesses across the bridges are compared and found to agree fairly well. The results are consistent with a simple picture in which the radio power and size of the radio lobe at the forward edge of the radio bridge are roughly time-independent for a given source, and the expansion of the bridge in the lateral direction is adiabatic. There is no indication that reacceleration or energy transport is important in the bridges of these sources. The rate of lateral expansion of the bridge just behind the radio lobe and hotspot in terms of the rate of forward propagation is compared with that predicted, and found to be in good agreement with the predicted value.

astro-ph↗

arXiv1995

FRII Radio Sources in Rich Clusters of Galaxies

A sample of FRII radio sources in rich clusters of galaxies, both at high (z$\sim$0.5) and low (z$\sim$0) redshift, has been constructed to study the effect of environment on radio sources. Comparisons are made between the properties of FRII sources in cluster and non-cluster environments, and between X-ray clusters with and without FRII sources. The principal results are the following: 1. Most low-redshift FRII sources in clusters appear to be similar to FRII sources in group or field environments in terms of radio power, optical properties of the host galaxy, and nonthermal pressure of the radio bridge. Most low-redshift clusters with FRII sources tend to lie at the lower end of cluster X-ray luminosity distribution, some having $L_x$ comparable to FRII sources in non-cluster environments. 2. High-redshift FRII sources are all quite similar to each other irrespective of their environments. The nonthermal pressures of their radio bridges appear to be similar to those of low-redshift FRII's. 3. The nonthermal pressures of the bridges of FRII sources appear to be similar to the thermal pressures of the ICM around them. This result would allow FRII sources to be used as probes of their gaseous environments. The current data imply that the evolution in the clustering strength around FRII sources toward high-redshift is likely to be closely linked to an evolution of the state of the intracluster medium.

astro-ph↗

arXiv1995

Cygnus A and Other 3CR Sources in Cosmological Tests

Powerful extended radio galaxies like Cygnus A can be used for cosmological tests. The characteristic, time-independent length $D_*$ for several radio sources is calculated and compared to the average physical length for a sample of radio galaxies. The ratio of these two lengths as a function of redshift is used to constrain cosmological parameters. Cygnus A is the only low-redshift ($z<0.5$) radio galaxy for which we have an estimate for $D_*$. We comment on the sensitivity to this one low-redshift point, and results including and excluding Cygnus A are shown. A low density universe is favored, and the one free model parameter is relatively well constrained.

astro-ph↗