Systematic effects in the extraction of the 'WMAP haze'

TL;DR

This paper investigates how systematic uncertainties in foreground subtraction can mimic the WMAP haze, cautioning against interpreting it as a physical phenomenon like dark matter annihilation.

Contribution

It highlights the potential for foreground subtraction errors to produce residuals similar to the haze, emphasizing the need for careful analysis.

Findings

Systematic uncertainties can produce residuals resembling the haze.

The residuals can have similar spectra and morphology to the haze.

Caution is needed when interpreting the haze as a physical signal.

Abstract

The extraction of a 'haze' from the WMAP microwave skymaps is based on subtraction of known foregrounds, viz. free-free (bremsstrahlung), thermal dust and synchrotron, each traced by other skymaps. While the 408 MHz all-sky survey is used for the synchrotron template, the WMAP bands are at tens of GHz where the spatial distribution of the radiating cosmic ray electrons ought to be quite different because of the energy-dependence of their diffusion in the Galaxy. The systematic uncertainty this introduces in the residual skymap is comparable to the claimed haze and can, for certain source distributions, have a very similar spectrum and latitudinal profile and even a somewhat similar morphology. Hence caution must be exercised in interpreting the 'haze' as a physical signature of, e.g., dark matter annihilation in the Galactic centre.