Other
Scientific paper
Aug 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007phdt........15r&link_type=abstract
Proquest Dissertations And Theses 2007. Section 0167, Part 0606 148 pages; [Ph.D. dissertation].United States -- Ohio: Ohio Uni
Other
X-Ray Bubbles, Galaxy Clusters, Radio Galaxies, Very Large Array
Scientific paper
We present an analysis of radio data for 24 radio galaxies observed with the Very Large Array (VLA) in at least 3 different frequencies. These systems possess prominent X-ray surface brightness depressions associated with cavities or bubbles that were created by interactions between powerful radio sources and the surrounding hot gas. We use the X-ray cavities to measure the mechanical jet power of radio sources over six decades of radio luminosity, independently of the radio properties themselves, which we measure from the VLA data.
Using these measurements, we examine the ratio between radio power and total jet power (the radiative efficiency). We find that the jet power increases with increasing radio power and that the radio sources in our sample are generally poor radiators, with radiative efficiencies ranging from 1 (Cygnus A) to 0.0001 (HCG 62). We argue that radio aging may be partly responsible for this wide range in the radiative efficiencies, in combination with intrinsic differences in the magnetic field strengths and the particle content ( k , the ratio between the heavy-particle energy and electron energy). We place limits on the magnetic field strengths and on the particle content of the radio lobes. We find that the magnetic field strengths derived under different assumptions (equipartition, pressure equilibrium, and by requiring the synchrotron age to be equal with the buoyancy age) are larger than the cluster wide magnetic field strengths, with the ones derived under pressure equilibrium being much larger than the others. In order for pressure-equilibrium magnetic field strengths to be equal with the equipartition magnetic field, the particle content ( k ) needs to vary from ~1 to 35000. Such high values of k support the idea of heavy jets. By comparing the synchrotron ages with the X-ray-derived ages, we find that the two ages are uncoupled, with the youngest systems, which may be in a driving stage, being better estimated by the synchrotron age. Having radio images in at least 3 frequencies, we are better able to classify a cavity as active, intermediate, or ghost based on the break frequency. However, because of the continuous range in break frequencies that we find, the separation of our sample into different categories is somewhat arbitrary. Lastly, we find that 327 MHz radio maps are typically better suited for tracing the cavity sizes than 1.4 GHz radio maps, and they are a promising proxy for X-ray cavities in systems where it is difficult to image the cavities directly in X- rays.
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