Andrew Young, Ph.D. 2004, M.S. 2001

Master's Thesis

Relativistic Electron Populations of Wide-Angle Tailed Radio Sources

by Andrew Young

Under the supervision of Professor Larry Rudnick

ABSTRACT

Color-color diagrams have been useful in studying the spectral shapes in radio galaxies. In this thesis, color-color diagrams presented for two wide-angle tailed radi o sources (WATs), 1231+674 and 1433+553, show that the standard aging models do not adequately represent the observed data. Although the Jaffe \& Perola and Karadshev -Pacholczyk models can explain some of the observed points in the color-color diagram, they do not account for those found near the power-law line. This difficulty ma y be attributable to several causes. Spectral tomography has been previously used to discern two separate electron populations in these sources. The combination spect ra from two such overlying components can easily resemble a power law. In addition, any non-uniformity in the magnetic field strength can also create a power-law-like spectrum. This thesis will also examine the possible origins of the spectra seen in the WATs and discuss the implications and constraints the results may have on cur rent aging analyses and WAT formation theories.

Ph.D Thesis

The Life Cycle of Radio Galaxies

by Andrew Young

Under the supervision of Professor Larry Rudnick

ABSTRACT

This thesis will examine some key issues in the life history of radio galaxies. The evolution of radio galaxies can be understood in terms of the history of their relativistic particle distributions and their morphologies. Using radio data from the Very Large Array (VLA), I begin by examining the relativistic particle acceleration processes in several Fanaroff-Riley I sources. The radio sources 1116+28, 1243+26, and 1553+24 all show dual spectral components known as jets and sheaths. These and other radio galaxies show that the strength of the acceleration mechanism approaches the strong shock limit for first order Fermi acceleration.

Active radio galaxies accelerate electrons that then undergo energy losses by way of synchrotron, adiabatic, and inverse-Compton mechanisms. I examine two radio sources (3C386, 3C98) whose structure may indicate that the acceleration process has recently ceased or is slowly coming to an end. An examination of these possibly dying radio sources with large, bright, and diffuse lobes reveals that the shape of the spectra indicates that their acceleration mechanisms approach the strong shock limit. With these derived low frequency spectral indices, an estimate of the true magnetic field strength in the lobes can be made should X-ray observations be available. This will alleviate the need to invoke equipartition assumptions.

Upon the end of the acceleration of electrons, a radio galaxy will eventually lose almost all of its relativistic electron energy through radiative, adiabatic, and Coulomb losses and evolve into a relic state. In this relic state, the radio galaxy may have no discernible radio core, radio jet, or optical counterpart. However, other mechanisms such as cluster merger shocks or re-started radio galaxies could re-energize these relic plasmas. An analysis of relic radio sources in the clusters Abell 85 and MKW 3s show that these processes do occur and reveal spectra that are consistent with weak shocks.

The sources studied here can be viewed as a snapshot in the timeline of a radio galaxy. The life cycles of radio galaxies have broad implications not just for themselves but also on the cluster environment. They contribute energy and particles into their surrounding cluster. In turn, the cluster environment also affects radio galaxies in life and death. I conclude with a summary of the role of radio galaxies in their cluster environments.