Galactic foreground contributions to the WMAP5 maps

TL;DR

This study analyzes WMAP5 data to characterize galactic foreground emissions, including synchrotron, dust, and free-free, revealing their intensity, spectral properties, and polarization fractions across different sky regions.

Contribution

It provides detailed measurements of foreground components' intensity, spectral indices, and polarization, highlighting the dominance of anomalous dust emission and constraining dust and free-free polarization.

Findings

Anomalous dust emission is dominant at low Galactic latitudes.

Synchrotron spectral index is approximately -3.3 in intensity.

Dust polarization fraction is less than 5% at 95% confidence.

Abstract

We compute the cross correlation of the intensity and polarisation from the 5-year WMAP data in different sky-regions with respect to template maps for synchrotron, dust, and free-free emission. We derive the frequency dependence and polarisation fraction for all three components in 48 different sky regions of HEALPix (Nside=2) pixelisation. The anomalous emission associated with dust is clearly detected in intensity over the entire sky at the K (23 GHz) and Ka (33 GHz) WMAP bands, and is found to be the dominant foreground at low Galactic latitude, between b=-40 and b=+10. The synchrotron spectral index obtained from the K and Ka WMAP bands from an all-sky analysis is -3.32\pm 0.12 for intensity and -3.01\pm0.03 for the polarised intensity. The polarisation fraction of the synchrotron is constant in frequency and increases with latitude from ~5% near the Galactic plane up to ~40% in some regions at high latitude; the average value for |b|<20 is 8.6\pm1.7 (stat) \pm0.5 (sys) % while for |b|>20 it is 19.3\pm0.8 (stat) \pm 0.5 (sys) %. Anomalous dust and free-free emission appear to be relatively unpolarised...[Abridged]...the average polarisation fraction of dust-correlated emission at K-band is 3.2\pm0.9 (stat) \pm 1.5 (sys) %, or less than 5% at 95% confidence. When comparing real data with simulations, 8 regions show a detected polarisation above the 99th percentile of the distribution from simulations with no input foreground polarisation, 6 of which are detected at above 2sigma and display polarisation fractions between 2.6% and 7.2%, except for one anomalous region, which has 32\pm12%. The dust polarisation values are consistent with the expectation from spinning-dust emission, but polarised dust emission from magnetic-dipole radiation cannot be ruled out. Free-free emission was found to be unpolarised with an upper limit of 3.4% at 95% confidence.