Diffuse radio sources in galaxy clusters: multi-wavelength observations

点击翻译按钮获取中文摘要

Radio relics are diffuse, low surface brightness, steep-spectrum sources that are typically located in the periphery of galaxy clusters. While it is known that non-thermal electrons are responsible for the observed synchrotron radiation, the mechanism of particle acceleration as well as the origins of the magnetic fields on these scales are poorly understood.The Low-Frequency Array (LOFAR) is the ideal instrument to find and study radio relics because it is very sensitive at low-frequencies and has a wide field of-view. With recent developments we are now capable of producing exquisite calibrated images that almost reach the thermal noise. As a point in case we have discovered with LOFAR diffuse emission in the low-mass galaxy cluster Abell 1931 which now wish to study in the X-rays and other radio bands (JVLA, GMRT) to investigate the origin of diffuse emission in galaxy clusters. Chandra observations for this target have already been approved. Since we do not know much about diffuse radio emission in lower mass clusters, this underlines the discovery potential of this target. So far, radio halos and relics have been found pre-dominantly in massive galaxy clusters.In a second part of this project, we will search for more steep-spectrum, diffuse emission in LOFAR Tier-1 surveys using direction-dependent calibration and imaging. A preliminary list of targets has been compiled from cross-correlating the area that has been surveyed by LOFAR Tier-1 survey with the Planck Sunyaev-Zeldovich cluster database yielding a total of 31 clusters. The discovery of new diffuse, steep spectrum sources will shed light on the role of old (fossil) relativistic electrons in producing radio relics.