Foreground contributions to the Cosmic Microwave

A detailed search has been made for evidence of residual foreground contributions to the Cosmic Microwave Background (CMB) WMAP (Bennett et al. 2003a,b), a map (nominally) cleaned for foreground already (Tegmark et al. 2003). We find positive results in that various features relate to Galactic properties. For example, 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◦ of the Plane and at higher latitudes. The mean temperature shows similar variations. An explanation in terms of Galactic effects seems inescapable. 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 (Hunter et al. 1997). We are mindful that the CMB maps examined (Tegmark et al. 2003) have already been ‘cleaned’ (for cosmic ray and other effects) in a rather complex way but, in our view, the cleaning has left potentially serious ’contaminations’. A correlation is found between gamma ray intensities and the CMB and other cosmic ray indicators. For example, regions of the Galaxy having (line of sight) steep cosmic ray energy spectra have low mean CMB temperatures and the important Loop I edge region, where the cosmic ray intensity is high, has a high mean temperature. 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 hypothesize 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 is briefly examined. The least that can be said is that the ’error’ in some of these properties has been underestimated.