Extragalactic Synchrotron Sources at Low Frequencies

The LWA will be well suited to address many important questions about the physics and astrophysics of extragalactic synchrotron sources. Good lowfrequency data will enable major steps forward in our understanding of radio galaxy physics, of the plasma in clusters of galaxies, and of active objects in the high-redshift universe. Such data will also be important in answering some basic questions about the physics of synchrotron-emitting plasmas. 1. General Introduction Synchrotron emission is one of our most important tools for understanding the active extragalactic universe. Energetic processes in many astrophysical settings create a relativistic, magnetized plasma which we can observe via its synchrotron emission. We can study the high-energy activity directly, for instance in the creation of a radio jet. We can use radio sources as probes of larger questions, for instance learning about the plasma atmosphere surrounding a radio tail by studying the dynamics of the radio tail, or understanding the dynamical state of the dark matter in a cluster of galaxies by studying the synchrotron halo in the cluster. We can study the population of massive black holes in the early universe through detections of high-redshift synchrotron sources. High quality images at low frequencies will be critical to all of these applications. In this paper we discuss some important contributions the LWA will make. One contribution is simple exploration. Many interesting sources are steep spectrum, and therefore can best be detected and studied at low frequencies. Multi-frequency imaging will be another important contribution, combining high-resolution images from the LWA with those from higher-frequency instruments such as the EVLA. We need good images across a broad frequency range, including the very low frequencies which the LWA will make available, in order to understand the nature and dynamics of radio jets on large and small scales. Finally, some fundamental questions regarding particle acceleration and the physics of synchrotron emission are still unresolved; good low-frequency data will be an important part of the answers. 2. Basic Synchrotron Physics If we want to use synchrotron emission to study active extragalactic sources, we need to understand the physics of the emitting plasma. Two important issues