The joint large-scale foreground-CMB posteriors of the 3-year WMAP data

TL;DR

This paper uses a Gibbs sampling approach to jointly analyze WMAP 3-year data, providing improved estimates of the CMB signal, foregrounds, and addressing instrumental offsets, with results consistent with previous findings.

Contribution

It introduces a new joint Bayesian method for CMB and foreground estimation that accounts for instrumental offsets and dipoles, improving upon prior models.

Findings

New estimate of the CMB power spectrum consistent with previous results.

Detection of a common spurious offset and a dipole in the data.

Foreground model aligns with the WMAP template-based model.

Abstract

Using a Gibbs sampling algorithm for joint CMB estimation and component separation, we compute the large-scale CMB and foreground posteriors of the 3-yr WMAP temperature data. Our parametric data model includes the cosmological CMB signal and instrumental noise, a single power law foreground component with free amplitude and spectral index for each pixel, a thermal dust template with a single free overall amplitude, and free monopoles and dipoles at each frequency. This simple model yields a surprisingly good fit to the data over the full frequency range from 23 to 94 GHz. We obtain a new estimate of the CMB sky signal and power spectrum, and a new foreground model, including a measurement of the effective spectral index over the high-latitude sky. A particularly significant result is the detection of a common spurious offset in all frequency bands of ~ -13muK, as well as a dipole in the V-band data. Correcting for these is essential when determining the effective spectral index of the foregrounds. We find that our new foreground model is in good agreement with template-based model presented by the WMAP team, but not with their MEM reconstruction. We believe the latter may be at least partially compromised by the residual offsets and dipoles in the data. Fortunately, the CMB power spectrum is not significantly affected by these issues, as our new spectrum is in excellent agreement with that published by the WMAP team. The corresponding cosmological parameters are also virtually unchanged.