Planck 2013 results. XII. Component separation

TL;DR

Planck 2013 XII Component Separation tackles separating the CMB from diffuse Galactic and extragalactic foregrounds across nine frequency bands. It implements four component-separation pipelines—Commander-Ruler, NILC, SEVEM, and SMICA—spanning pixel- and harmonic-space approaches, and validates them with extensive Full Focal Plane simulations (FFP6) and internal cross-consistency checks. The CMB maps achieve robust recovery over about 73% of the sky and up to multipoles $l \lesssim 2000$, with cosmological parameters computed in a $\Lambda$CDM framework in agreement with cross-spectrum Planck likelihoods; residual foregrounds are modeled by a two-parameter spectrum, with a low-frequency power-law and a one-component dust model. The analysis also yields full-sky diffuse Galactic foreground maps (low-frequency, CO, and thermal dust) and a low-frequency spectral-index map that traces dominated components (synchrotron, AME, free-free) and their spatial variation, enabling targeted astrophysical studies and follow-up observations.

Abstract

Planck has produced detailed all-sky observations over nine frequency bands between 30 and 857 GHz. These observations allow robust reconstruction of the primordial cosmic microwave background (CMB) temperature fluctuations over nearly the full sky, as well as new constraints on Galactic foregrounds. This paper describes the component separation framework adopted by Planck. We test four foreground-cleaned CMB maps derived using qualitatively different component separation algorithms. The quality of our reconstructions is evaluated through detailed simulations and internal comparisons, and shown through various tests to be internally consistent and robust for CMB power spectrum and cosmological parameter estimation up to l = 2000. The parameter constraints on LambdaCDM cosmologies derived from these maps are consistent with those presented in the cross-spectrum based Planck likelihood analysis. We choose two of the CMB maps for specific scientific goals. We also present maps and frequency spectra of the Galactic low-frequency, CO, and thermal dust emission. The component maps are found to provide a faithful representation of the sky, as evaluated by simulations. For the low-frequency component, the spectral index varies widely over the sky, ranging from about beta = -4 to -2. Considering both morphology and prior knowledge of the low frequency components, the index map allows us to associate a steep spectral index (beta < -3.2) with strong anomalous microwave emission, corresponding to a spinning dust spectrum peaking below 20 GHz, a flat index of beta > -2.3 with strong free-free emission, and intermediate values with synchrotron emission.

Figures (1)

• Figure 1: Foreground-cleaned CMB maps derived by Commander-Ruler, NILC, SEVEM and SMICA. Note that the SMICA map has been filled in smoothly inside a 3% Galactic mask.