Planck 2013 results. XXI. All-sky Compton parameter power spectrum and high-order statistics

TL;DR

The Planck 2013 results XXII present the first all-sky Compton y map from Planck frequencies (100–857 GHz) and quantify the thermal SZ signal through its power spectrum and higher-order statistics. They employ MILCA and NILC component separation to extract the y-map, validate against Planck SZ clusters, and model foregrounds with FFP6 simulations, enabling a measurement of the tSZ power spectrum over 0.17°–3.0° and independent skewness/bispectrum analyses. The analysis yields a cosmological constraint on the combination σ8(Ωm/0.28)^{0.40}≈0.784±0.016 (power spectrum) and σ8≈0.779±0.015 (skewness) or σ8≈0.74±0.04 (bispectrum), indicating a mild tension with primary CMB-derived values, potentially due to mass-bias and foreground modelling. Overall, the work demonstrates Planck’s capability to probe the integrated tSZ signal from both detected and unresolved clusters and diffuse gas, informing the gas content in halos and large-scale structure on all scales.

Abstract

We have constructed the first all-sky map of the thermal Sunyaev-Zeldovich (tSZ) effect by applying specifically tailored component separation algorithms to the 100 to 857 GHz frequency channel maps from the Planck survey. These maps show an obvious galaxy cluster tSZ signal that is well matched with blindly detected clusters in the Planck SZ catalogue. To characterize the signal in the tSZ map we have computed its angular power spectrum. At large angular scales ($\ell < 60$), the major foreground contaminant is the diffuse thermal dust emission. At small angular scales ($\ell > 500$) the clustered Cosmic Infrared Background (CIB) and residual point sources are the major contaminants. These foregrounds are carefully modelled and subtracted. We measure the tSZ power spectrum in angular scales, $0.17^{\circ} \lesssim θ\lesssim 3.0^{\circ}$, that were previously unexplored. The measured tSZ power spectrum is consistent with that expected from the Planck catalogue of SZ sources, with additional clear evidence of signal from unresolved clusters and, potentially, diffuse warm baryons. We use the tSZ power spectrum to obtain the following cosmological constraints: $σ_8(Ω_{\mathrm{m}}/0.28)^{3.2/8.1}=0.784 \pm 0.016 (68% C.L.). Marginalized band-powers of the Planck tSZ power spectrum and the best-fit model are given. The non-Gaussianity of the Compton parameter map is further characterized by computing its 1D probability distribution function and its bispectrum. These are used to place additional independent constraints on $σ_{8}$.

Figures (16)

• Figure 1: Reconstructed Planck all-sky Compton parameter maps for NILC (top) and MILCA (bottom) in orthographic projections. The apparent difference in contrast observed between the NILC and MILCA maps comes from differences in the instrumental noise contribution and foreground contamination and from the differences in the filtering applied for display purpose to the original Compton parameter maps.
• Figure 2: A small region of the reconstructed Planck all-sky Compton parameter maps for NILC (left) and MILCA (right) at intermediate Galactic latitudes in the southern sky.
• Figure 3: Comparison of the measurements of $Y_{5R500}$. Left: the values derived from the detection methods used to build the Planck catalogue of clusters ($Y_{5R500,\mathrm{PSZ}}$), plotted against those from the all-sky reconstructed MILCA tSZ map ($Y_{5R500,y\mathrm{-MAP}}$). Right: the MILCA ($Y_{5R500,\mathrm{MILCA}}$) versus NILC ($Y_{5R500,\mathrm{NILC}}$) all-sky tSZ effect maps. The equality relationship is marked as a dashed black line. A least-squares bisector method fit to the data lead to slopes of $1.09\pm 0.02$ and $1.08\pm0.02$ for the MILCA and NILC Compton parameter maps, respectively.
• Figure 4: Angular power spectrum of the main foreground contributions as estimated using the FFP6 simulations. We plot the diffuse Galactic emission (blue), clustered CIB (green) and point source (cyan) contributions, as well as the tSZ signal (red). The solid and dotted lines correspond to the NILC F/L and to the NILC- MILCA F/L cross-power spectra, respectively. For illustration we also show the Planck instrumental noise auto-power spectrum (dashed black line) in the MILCA Compton parameter map.
• Figure 5: Angular cross-power spectra of the PlanckNILC F/L reconstructed Compton parameter maps for different Galactic masks, removing 30% (cyan), 40% (black points and error bars), 50% (red), 60% (green), and 70% (blue) of the sky.