Tomography of galaxy clusters through low-frequency radio polarimetry

Promotie: dhr. R.F. Pizzo, 14.45 uur, Academiegebouw, Broerstraat 5, Groningen
Proefschrift: Tomography of galaxy clusters through low-frequency radio polarimetry
Promotor(s): prof.dr. A.G. de Bruyn
Faculteit: Wiskunde en Natuurwetenschappen
Contact: Roberto Pizzo, tel. 050-363 8324, e-mail: pizzo@astro.rug.nl

Tomography of galaxy clusters through low-frequency radio polarimetry

Galaxy clusters are the most massive bound objects in the universe. As the result of several merger events they are not static, but instead grow and still form at the present epoch. When observed at radio wavelengths, some merging and/or post-merger galaxy clusters host extended diffuse features whose origin and evolution is not yet understood. They have been classified as halos and relics, depending on their morphology, polarization and location within the cluster. We observed the galaxy clusters Abell 2255 and Coma to study their halo and relic sources in polarization and total intensity.

This thesis represents the first successful attempt to unveil the 3-D structure of galaxy clusters through low-frequency radio polarimetry. By using a new technique of analysis of the polarization data called RM-synthesis, we revealed the nature and location along the line of sight of several structures belonging to Abell 2255 and our Galaxy. At frequencies below 350 MHz, we detected in total intensity several new extended features in both clusters. Some of them are likely associated with shocks deriving from the accretion of gas from the cosmic environment into the clusters. Others, on the other hand, are suggested to be the first example of a new class of very old cluster objects. Such structures are expected to be detected in more galaxy clusters, but at very low frequencies only. The Low Frequency Array (LOFAR) will be the key instrument to further investigate with unprecedented resolution and sensitivity the important properties shown by Abell 2255 and Coma.