Foreground contributions to the Cosmic Microwave Background

Abstract

A detailed search has been made for evidence of foreground contributions to the Cosmic Microwave Background (CMB) WMAP, such foregrounds being related to our Galaxy. We find remarkable results. On the largest angular scales we find significant differences between the power in the fluctuations for positive and negative Galactic latitudes and between the four Galactic Quadrants. There are also differences between the power spectrum at latitudes within 10 deg of the Plane and at higher latitudes. The `slope' of the power spectrum has similar variations. In an effort to find the origin of these Galactic-style effects we have examined the evidence from Galactic gamma rays, specifically from the EGRET instrument. A correlation is found between gamma ray intensities and the CMB and other cosmic ray indicators. Most of the large scale Galactic asymmetries (eg north, south difference and Quadrant variations) have analogues in cosmic ray asymmetries and also in some other Galactic properties, such as the column density of gas. Thus, it is possible to hypothesise on direct cosmic ray-induced contributions, although it may be that cosmic rays are simply the indicators of Galactic `conditions' which are influencing the residual CMB fluctuations. Irrespective of the actual cause of the correlations we have endeavoured to extrapolate to the situation where the residual foreground is minimised. The effect on the usually-derived cosmological properties - universal matter content, ionization, the tensor contribution, tilt and curvature - is briefly examined.