Fluctuations in the Radio Background from Intergalactic Synchrotron Emission

The shocks produced in the intergalactic medium during large-scale structureformation accelerate a population of highly relativistic electrons which emitsynchrotron radiation due to intergalactic magnetic fields. In a previous paper(Loeb & Waxman 2000) we have shown that these electrons cool primarily byinverse-Compton scattering of the microwave background photons and can therebyproduce the observed intensity and spectrum of the diffuse gamma-raybackground. Here we calculate the intensity and angular fluctuations of theradio synchrotron background that results from the same high-energy electrons,as well as the expected angular fluctuations in the gamma-ray background. Onangular scales smaller than a degree, the predicted fluctuations in themicrowave background temperature are of order 40micro-K*(xi_B/0.01)(nu/10GHz)^{-3}, where xi_B is the magnetic fraction of the post-shock energydensity. This foreground might have already dominated the anisotropy signaldetected in existing low-frequency CMB experiments, and can be identified withconfidence through multi-frequency observations. Detection of the synchrotronfluctuations would allow to determine the strength of the intergalacticmagnetic field. We predict a strong correlation between high-resolution mapstaken at low-frequency radio waves and at high-energy gamma-rays. Young X-rayclusters may also appear as radio or gamma-ray clusters. The detailed study ofthis correlation will become easily accessible with the future launch of GLAST.Comment: 11 pages, 2 figures, submitted to ApJ