Foreground contributions to the cosmic microwave background

Abstract

A detailed search has been made for evidence of residual foreground contributions to the cosmic microwave background (CMB) in the map generated by the Wilkinson Microwave Anisotropy Probe (WMAP), a map that has been (nominally) cleaned for the foreground already. 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 evidence from Galactic gamma‐rays, specifically from the EGRET instrument. We are mindful that the CMB maps examined have already been ‘cleaned’ (for CR and other effects) in a rather complex way, but, in our view, the cleaning has left some potentially serious ‘contaminations’. A correlation is found between gamma‐ray intensities and the CMB and other CR indicators. For example, regions of the Galaxy having (line‐of‐sight) steep CR energy spectra have low mean CMB temperatures, and the important Loop I edge region, where the CR intensity is high, has a high mean temperature. Most of the large‐scale Galactic asymmetries (e.g. north–south difference and quadrant variations) have analogues in CR asymmetries and also in some other Galactic properties, such as the column density of gas. Thus, it is possible to hypothesize about direct CR‐induced contributions, although it may be that CRs 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 minimized. 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.

Cosmic ray contribution in the WMAP of the cosmic microwave background

“…In our recent publication ( [10]), which confirmed results reported by us about ten years ago ( [9]) with the one-year only WMAP data, Tegmark, de Oliviera-Costa & Hamilton [8], we have shown that there is strong evidence that the procedure of eliminating the known and identified foreground contributions is not perfect. We have found some contributions from large Galactic structures which have not been taken into account yet.…”

“…We supposed that the EGRET map (with point sources excluded) is a view of the possible foreground on CMB maps caused by the cosmic rays and Galactic matter structures. The correlation between the EGRET gamma ray flux and the temperature fluctuations measured in this direction by WMAP was used in our previous papers [9,10]. We have followed this way of constructing the sky map of the respective correlation coefficients for the polarization parameters of WMAP.…”

Mapping the large-scale anisotropy in the WMAP data

“…• , l = 237 • ) (Bunn & Scott 2000;Copi et al 2004;Eriksen et al 2004a;Hansen et al 2004a,b;Wibig 2005;Land & Magueijo 2005a,b;Schwarz et al 2004;Prunet et al 2005;Donoghue & Donoghue 2005), as well as indications 1 Throughout this paper we use galactic coordinates with origin at b = 90…”

Search for correlations of GRB and cosmic rays

“…Indeed, a correlation is found (Wibig and Wolfendale 2005) between the CMB (Hinshaw et al 2006) temperature and gamma ray intensities (Cillis and Hartman 2005) 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.…”