Cosmology & Astrophysics on Large Scales

1:- We have detected evidence for the largest void in the known universe with WMAP, NVSS, and the ISW effect (Rudnick, Brown & Williams 2007). We used this void to explain the non-Gaussian ``cold spot" in the WMAP CMB data. This result has proven to be highly controversial, as can be seen in several of the direct responses to the paper.

2:- We explored, for the first time, the method of cross-correlation of radio synchrotron emission and tracers of large-scale structure in order to detect cosmological shocks in the Warm-Hot Intergalactic Medium (WHIM; Brown, Farnsworth & Rudnick 2010). As chair of the Cosmology and Low Surface-brightness working groups for the EMU survey, I am coordinating the effort to make such a measurement over 75% of the sky to constrain the origin of cosmological magnetic fields. This includes such issues as dealing with the noise covariance matrix of a (potentially) 3x10^9 pixel Healpix map of the sky, and is part of a broader effort I have initiated to apply sophisticated cosmological model inference to standard radio astronomy data (e.g., the Bayesian rotation-measure work below). These methods are directly applicable to CMB/LSS cross-correlation, and the search for the late ISW effect.

Clusters of Galaxies

3:- We detected the first structure-formation shock (seen as a ``radio relic") that is not associated with a rich cluster of galaxies (Brown & Rudnick 2009). This object was the second of a new class of diffuse cluster emission that does not follow the observed radio/x-ray luminosity correlation (e.g., Brunetti et al. 2009).

4:- We detected two new shock structures in the famous Coma Cluster of galaxies (Brown & Rudnick 2010), one of which has subsequently been identified in X-rays (Markevitch et al. 2010) and recently by Planck. We have also identified a curious correspondence between the synchrotron halo of Coma and its weak-lensing derived Dark Matter projection.

350 MHz WSRT contours of the diffuse radio emission in the Coma cluster of galaxies ove ROSAT diffuse X-rays. The sharp Western edge in both the radio and X-rays is likely due to shocked Intracluster medium (ICM).

Synchrotron Polarization

4:- We have demonstrated that an unconventional reprocessing of the NVSS polarization survey could reveal structures on scales from 15&prime to hundreds of degrees (far larger than the nominal shortest-baseline scale Rudnick & Brown 2009). This has yielded hundreds of new diffuse sources as well as the identification of a new nearby galactic loop. This method is sensitive to small-scale polarized fluctuations on scales not accessible to current all-sky observations, and can potentially be used to identify polarized CMB foreground errors at high l.

The NVSS survey in polarized intensity convolved to 13', revealing large-scale polarized fluctuations.