Probing large-scale structure with radio observations.

Abstract

This thesis focuses on detecting magnetized relativistic plasma in the intergalactic medium (IGM) of filamentary large-scale structure (LSS) by observing the synchrotron emission emitted by structure formation shocks. Little is known about the IGM beyond the largest clusters of galaxies, and synchrotron emission holds enormous promise as a means of probing magnetic fields and relativistic particle populations in these low density regions.

I'll first report on observations taken at the Very Large Array and the Westerbork Synthesis Radio Telescope of the diffuse radio source 0809+39. I use these observations to demonstrate that 0809+39 is likely the first &ldquoradio relic&rdquo discovered that is not associated with a rich X-ray emitting cluster of galaxies.

I then demonstrate that an unconventional reprocessing of the NVSS polarization survey could reveal structures on scales from 15&rsquo to hundreds of degrees, far larger than the nominal shortest-baseline scale. This has yielded hundreds of new diffuse sources as well as the identification of a new nearby galactic loop.

These observations also highlight the major obstacle that diffuse galactic foreground emission poses for any search for large-scale, low surface-brightness extragalactic emission. I therefore explore the cross-correlation of diffuse radio emission with optical tracers of LSS as a means of statistically detecting the presence of magnetic fields in the low-density regions of the cosmic web. This initial study with the Bonn 1.4&simGHz radio survey yields an upper limit of 0.2&sim&muG for large-scale filament magnetic fields.

Finally, I report on new Green Bank Telescope and Westerbork Synthesis Radio Telescope observations of the famous Coma cluster of galaxies. Major findings include an extension to the Coma cluster radio relic source 1253+275 which makes its total extent &sim2~Mpc, as well as a sharp edge, or &ldquofront&rdquo, on the Western side of the radio halo which shows a strong correlation with merger activity associated with an infalling sub-cluster. This front is just interior to a temperature jump derived from XMM-Newton observations, and may be related to shocked infalling gas.