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Department of Physics

Staff profile

Publication details for Prof Sir Arnold Wolfendale

Wibig, T. & Wolfendale, A. W. (2005). Foreground contributions to the cosmic microwave background. Monthly Notices of the Royal Astronomical Society 360(1): 236-252.

Author(s) from Durham

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 degrees 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.