Cross-Correlation of Diffuse Synchrotron and Large-Scale Structures
  We explore for the first time the method of cross-correlation of radio
synchrotron emission and tracers of large-scale structure in order to detect
the diffuse IGM/WHIM. We performed a cross-correlation of a 34 x 34 degree area
of 2MASS galaxies for two redshift slices (0.03 < z < 0.04 and 0.06 < z < 0.07)
with the corresponding region of the 1.4 GHz Bonn survey. For this analysis, we
assumed that the synchrotron surface brightness is linearly proportional to
surface density of galaxies. We also sampled the cross-correlation function
using 24 distant fields of the same size from the Bonn survey, to better assess
the noise properties. Though we obtained a null result, we found that by adding
a signal weighted by the 2MASS image with a filament (peak) surface brightness
of 1 (7) mK and 7 (49) mK would produce a 3 sigma positive correlation for the
0.03 < z < 0.04 and 0.06 < z < 0.07 redshift slices respectively. These
detection thresholds correspond to minimum energy magnetic fields as low as 0.2
microG, close to some theoretical expectations for filament field values. This
injected signal is also below the rms noise of the Bonn survey, and
demonstrates the power of this technique and its utility for upcoming sensitive
continuum surveys such as GALFACTS at Arecibo and those planned with the
Murchison Widefield Array (MWA).
