LOFAR Scientific Memorandum Number 1: Cluster-Formation Synchrotron Radiation. A Contaminant for Epoch of Reionization Experiments and a Signal for Probing Cluster Formation and the Gamma-Ray Background

摘要

The process of assembly of the largest clusters of galaxies, M approx. greater than 10(exp 14) solar mass, should have produced shocks that accelerated electrons to TeV energies. In turn, these electrons will produce synchrotron emission. A recent analysis by Waxman and Loeb predicts that this intergalactic synchrotron background will have an amplitude of order 10K and characteristic fluctuation size of 0.1 deg-1 deg at frequencies near 100MHz. This cluster-formation synchrotron radiation can be targeted in LOFAR and SKA observations as a source of information on cluster formation that will complement detailed gamma-ray studies. Existing low-frequency VLA observations already have detected what are probably the brightest examples of such cluster- formation synchrotron radiation. Conversely, the predicted amplitude of the cluster-formation synchrotron radiation is roughly 100 times larger than that predicted for the signature of the epoch of reionization in the (redshifted) H I line, but the angular scales are comparable. We suggest two strategies that may, singly or in combination, suffice to remove this contaminant from experiments designed to detect or map the H I signature of the EoR. Either strategy is demanding, though, as the accuracies required are probably 1 part in 5000 or better.