The new low frequency radio telescope LOFAR; probing merging clusters By Huub Rottgering (Leiden Observatory)

LOFAR, the Low Frequency Radio Array, is a pan-European radio telescope that is currently being commissioned. At the end of 2011 the array will consist of 36 stations out to ~ 100 km within the Netherlands and 8 international stations in Germany (5), France, Sweden and the United Kingdom. Operating at frequencies from 30 to 200 MHz, LOFAR will provide enormous improvements over previous facilities in the following three regions of parameter space:

  • Very Low Frequencies, with - 3 orders of magnitude improvement in both sensitivity and angular resolution. This is a mostly unexplored spectral region that is uniquely sensitive to ultra-steep spectrum z>6 radio galaxies, diffuse emission from clusters and the oldest `fossil' synchrotron electrons.
  • Size of the Instantaneous Field of View, of many tens of square degrees. This will deliver a transformational increase in speed to survey the radio sky, crucially important for the quest for rare objects such as distant clusters, proto-clusters and z > 6 radio galaxies.
  • Low-Frequency Radio Spectroscopy, enabling studies of redshifted neutral hydrogen at the Epoch of Reionisation.

In the first part of the talk I will briefly review the status of LOFAR. In the second part of the talk if will discuss how radio observations of clusters are important to understand the impact of shocks and mergers on the general evolution of clusters. In the last two years we have embarked on a large project to elucidate the relation of the diffuse radio relics and properties of the ICM. We will discuss results on studies of individual clusters and show that shocks produced in cluster mergers are clearly related to the presence of diffuse radio emission. We then present results from a study of a sample of relics. Using this sample, we found clear relations between the various properties of the relics (the Mach number of merger shocks as traced by the radio spectral index, projected distance from the cluster center and the radio power).

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