Mon. Not. R. Astron. Soc., 467, 4914-4936 (2017/June-1)
Low-frequency radio constraints on the synchrotron cosmic web.
VERNSTROM T., GAENSLER B.M., BROWN S., LENC E. and NORRIS R.P.
Abstract (from CDS):
We present a search for the synchrotron emission from the synchrotron cosmic web by cross-correlating 180-MHz radio images from the Murchison Widefield Array with tracers of large-scale structure (LSS). We use two versions of the radio image covering 21.○76 x 21.○76 with point sources brighter than 0.05 Jy subtracted, with and without filtering of Galactic emission. As tracers of the LSS, we use the Two Micron All-Sky Survey and the Wide-field InfraRed Explorer redshift catalogues to produce galaxy number density maps. The cross-correlation functions all show peak amplitudes at 0°, decreasing with varying slopes towards zero correlation over a range of 1°. The cross-correlation signals include components from point source, Galactic, and extragalactic diffuse emission. We use models of the diffuse emission from smoothing the density maps with Gaussians of sizes 1-4 Mpc to find limits on the cosmic web components. From these models, we find surface brightness 99.7 per cent upper limits in the range of 0.09-2.20 mJy beam–1 (average beam size of 2.6 arcmin), corresponding to 0.01-0.30 mJy arcmin–2. Assuming equipartition between energy densities of cosmic rays and the magnetic field, the flux density limits translate to magnetic field strength limits of 0.03-1.98 µG, depending heavily on the spectral index. We conclude that for a 3σ detection of 0.1 µG magnetic field strengths via cross-correlations, image depths of sub-mJy to sub-µJy are necessary. We include discussion on the treatment and effect of extragalactic point sources and Galactic emission, and next steps for building on this work.
© 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
methods: statistical - cosmology: observations - diffuse radiation - large-scale structure of Universe - radio continuum: general - radio continuum: general
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