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Register a new userModelling the Polarisation of Microwave Foreground Emission on Large Angular Scales
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Templates for polarised emission from Galactic foregrounds at frequencies relevant to Cosmic Microwave Background (CMB) polarisation experiments are obtained by modelling the Galactic Magnetic Field (GMF) on large scales. This work extends the results of ODea et al. by including polarised synchrotron radiation as a source of foreground emission. The polarisation direction and fraction in this calculation are based solely on the underlying choice of GMF model and therefore provide an independent prediction for the polarisation signal on large scales. Templates of polarised foregrounds may be of use when forecasting effective experimental sensitivity. In turn, as measurements of the CMB polarisation over large fractions of the sky become routine, this model will allow for the data to constrain parameters in the, as yet, not well understood form of the GMF.
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The upcoming generation of cosmic microwave background (CMB) experiments face a major challenge in detecting the weak cosmic B-mode signature predicted as a product of primordial gravitational waves. To achieve the required sensitivity these experiments must have impressive control of systematic effects and detailed understanding of the foreground emission that will influence the signal. In this paper, we present templates of the intensity and polarisation of emission from one of the main Galactic foregrounds, interstellar dust. These are produced using a model which includes a 3D description of the Galactic magnetic field, examining both large and small scales. We also include in the model the details of the dust density, grain alignment and the intrinsic polarisation of the emission from an individual grain. We present here Stokes parameter template maps at 150GHz and provide an on-line repository (http://www.imperial.ac.uk/people/c.contaldi/fgpol) for these and additional maps at frequencies that will be targeted by upcoming experiments such as EBEX, Spider and SPTpol.
We cross-correlate the Saskatoon Ka and Q-Band Cosmic Microwave Background (CMB) data with different maps to quantify possible foreground contamination. We detect a marginal correlation (2 sigma) with the Diffuse Infrared Background Experiment (DIRBE) 240, 140 and 100 microm maps, but we find no significant correlation with point sources, with the Haslam 408 MHz map or with the Reich and Reich 1420 MHz map. The rms amplitude of the component correlated with DIRBE is about 20% of the CMB signal. Interpreting this component as free-free emission, this normalization agrees with that of Kogut et al. (1996a; 1996b) and supports the hypothesis that the spatial correlation between dust and warm ionized gas observed on large angular scales persists to smaller angular scales. Subtracting this contribution from the CMB data reduces the normalization of the Saskatoon power spectrum by only a few percent.
Primordial magnetic fields lead to non-Gaussian signals in the Cosmic Microwave Background (CMB) even at the lowest order, as magnetic stresses, and the temperature anisotropy they induce, depend quadratically on the magnetic field. In contrast, CMB non-Gaussianity due to inflationary scalar perturbations arise only as a higher order effect. We propose here a novel probe of stochastic primordial magnetic fields that exploits the characteristic CMB non-Gaussianity that they induce. In particular, we compute the CMB bispectrum ($b_{l_{_1}l_{_2}l_{_3}}$) induced by stochastic primordial fields on large angular scales. We find a typical value of $l_1(l_1+1)l_3(l_3+1) b_{l_{_1}l_{_2}l_{_3}} sim 10^{-22}$, for magnetic fields of strength $B_0 sim 3$ nano Gauss and with a nearly scale invariant magnetic spectrum. Current observational limits on the bispectrum allow us to set upper limits on $B_0 sim 35$ nano Gauss, which can be improved by including other magnetically induced contributions to the bispectrum.
We present ForSE (Foreground Scale Extender), a novel Python package which aims at overcoming the current limitations in the simulation of diffuse Galactic radiation, in the context of Cosmic Microwave Background experiments (CMB). ForSE exploits the ability of generative adversarial neural networks (GANs) to learn and reproduce complex features present in a set of images, with the goal of simulating realistic and non-Gaussian foreground radiation at sub-degree angular scales. This is of great importance in order to estimate the foreground contamination to lensing reconstruction, de-lensing and primordial B-modes, for future CMB experiments. We applied this algorithm to Galactic thermal dust emission in both total intensity and polarization. Our results show how ForSE is able to generate small scale features (at 12 arc-minutes) having as input the large scale ones (80 arc-minutes). The injected structures have statistical properties, evaluated by means of the Minkowski functionals, in good agreement with those of the real sky and which show the correct amplitude scaling as a function of the angular dimension. The obtained thermal dust Stokes Q and U full sky maps as well as the ForSE package are publicly available for download.
We describe SPIDER, a balloon-borne instrument to map the polarization of the millimeter-wave sky with degree angular resolution. Spider consists of six monochromatic refracting telescopes, each illuminating a focal plane of large-format antenna-coupled bolometer arrays. A total of 2,624 superconducting transition-edge sensors are distributed among three observing bands centered at 90, 150, and 280 GHz. A cold half-wave plate at the aperture of each telescope modulates the polarization of incoming light to control systematics. Spiders first flight will be a 20-30-day Antarctic balloon campaign in December 2011. This flight will map sim8% of the sky to achieve unprecedented sensitivity to the polarization signature of the gravitational wave background predicted by inflationary cosmology. The Spider mission will also serve as a proving ground for these detector technologies in preparation for a future satellite mission.
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