Constraints on a stochastic background of primordial magnetic fields with WMAP and South Pole Telescope data

We constrain a stochastic background of primordial magnetic fields (PMF) by its contribution to the cosmic microwave background (CMB) anisotropy angular power spectrum with the combination of WMAP 7 year and South Pole Telescope (SPT) data. The contamination in the SPT data by unresolved point sources and by the Sunyaev-Zeldovich (SZ) effect due to galaxy clusters has been taken into account as modelled by the SPT Collaboration. With this combination of WMAP 7 year and SPT data, we constrain the amplitude Gaussian smoothed over 1 Mpc scale of a stochastic background of non-helical PMF to B-1 Mpc < 3.5 nG at 95% confidence level, improving on previous bounds. Our analysis shows that SPT data up to l = 3000 bring an improvement of almost a factor two with respect to results with previous CMB high-l data. We then discuss the forecasted impact from unresolved points sources and SZ effect for PLANCK capabilities in constraining PMF. (C) 2013 Elsevier B.V. All rights reserved.