MILCA, a modified internal linear combination algorithm to extract astrophysical emissions from multifrequency sky maps

Arnaud

et al. 2013

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Taking advantage of the all-sky coverage and broad frequency range of the Planck satellite, we study the Sunyaev-Zeldovich (SZ) and pressure profiles of 62 nearby massive clusters detected at high significance in the 14-month nominal survey. Careful reconstruction of the SZ signal indicates that most clusters are individually detected at least out to R 500 . By stacking the radial profiles, we have statistically detected the radial SZ signal out to 3 × R 500 , i.e., at a density contrast of about 50-100, though the dispersion about the mean profile dominates the statistical errors across the whole radial range. Our measurement is fully consistent with previous Planck results on integrated SZ fluxes, further strengthening the agreement between SZ and X-ray measurements inside R 500 . Correcting for the effects of the Planck beam, we have calculated the corresponding pressure profiles. This new constraint from SZ measurements is consistent with the X-ray constraints from XMM-Newton in the region in which the profiles overlap (i.e., [0.1-1] R 500 ), and is in fairly good agreement with theoretical predictions within the expected dispersion. At larger radii the average pressure profile is slightly flatter than most predictions from numerical simulations. Combining the SZ and X-ray observed profiles into a joint fit to a generalised pressure profile gives best-fit parameters [P 0 , c 500 , γ, α, β] = [6.41, 1.81, 0.31, 1.33, 4.13]. Using a reasonable hypothesis for the gas temperature in the cluster outskirts we reconstruct from our stacked pressure profile the gas mass fraction profile out to 3 R 500 . Within the temperature driven uncertainties, our Planck constraints are compatible with the cosmic baryon fraction and expected gas fraction in halos. Key words. cosmology: observations -galaxies: clusters: general -galaxies: clusters: intracluster medium -submillimeter: general -X-rays: general Appendices are available in electronic form at

Section: Appendix A: Sz Map Reconstruction Methodsmentioning

confidence: 99%

Planckintermediate results

Arnaud

et al. 2013

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“…We selected a sample of cluster pairs whose difference in redshift is smaller than 0.01 and whose angular distance is between 10 and 120 . For all selected pairs we constructed maps of the tSZ (tSZ hereafter) emission from the Planck HFI frequency maps at a resolution of 7.18 using different component separation techniques: MILCA (maximum internal linear component analysis, Hurier et al 2010), NILC (needlet internal linear combination, Remazeilles et al 2011) and GMCA (generalized morphological component analysis, Bobin et al 2008). A detailed discussion of the relative performance of these component separation techniques can be found in Planck Collaboration (2013) and Melin et al (2012).…”

Section: Pairs Of Merging Clusters In Planckmentioning

confidence: 99%

Planckintermediate results

Collaboration¹,

et al. 2013

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Context. About half of the baryons of the Universe are expected to be in the form of filaments of hot and low-density intergalactic medium. Most of these baryons remain undetected even by the most advanced X-ray observatories, which are limited in sensitivity to the diffuse low-density medium. Aims. The Planck satellite has provided hundreds of detections of the hot gas in clusters of galaxies via the thermal Sunyaev-Zel'dovich (tSZ) effect and is an ideal instrument for studying extended low-density media through the tSZ effect. In this paper we use the Planck data to search for signatures of a fraction of these missing baryons between pairs of galaxy clusters. Methods. Cluster pairs are good candidates for searching for the hotter and denser phase of the intergalactic medium (which is more easily observed through the SZ effect). Using an X-ray catalogue of clusters and the Planck data, we selected physical pairs of clusters as candidates. Using the Planck data, we constructed a local map of the tSZ effect centred on each pair of galaxy clusters. ROSAT data were used to construct X-ray maps of these pairs. After modelling and subtracting the tSZ effect and X-ray emission for each cluster in the pair, we studied the residuals on both the SZ and X-ray maps. Results. For the merging cluster pair A399-A401 we observe a significant tSZ effect signal in the intercluster region beyond the virial radii of the clusters. A joint X-ray SZ analysis allows us to constrain the temperature and density of this intercluster medium. We obtain a temperature of kT = 7.1 ± 0.9 keV (consistent with previous estimates) and a baryon density of (3.7 ± 0.2) × 10 −4 cm −3 . Conclusions. The Planck satellite mission has provided the first SZ detection of the hot and diffuse intercluster gas.

“…The Comptonisation parameter y maps used in this work have been obtained using the MILCA (modified internal linear combination algorithm) method (Hurier et al 2010) on the Planck frequency maps from 100 GHz to 857 GHz in a region centred on the Coma cluster. MILCA is a component separation approach aimed at extracting a chosen component (in our case the thermal Sunyaev Zeldovich, tSZ, signal) from a multi-channel set of input maps.…”

Section: Reconstruction and Analysis Of The Y Mapmentioning

confidence: 99%

Planckintermediate results

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We present an analysis of Planck satellite data on the Coma cluster observed via the Sunyaev-Zeldovich effect. Thanks to its great sensitivity, Planck is able, for the first time, to detect SZ emission up to r ≈ 3 × R 500 . We test previously proposed spherically symmetric models for the pressure distribution in clusters against the azimuthally averaged data. In particular, we find that the Arnaud et al. (2010, A&A, 517, A92) "universal" pressure profile does not fit Coma, and that their pressure profile for merging systems provides a reasonable fit to the data only at r < R 500 ; by r = 2 × R 500 it underestimates the observed y profile by a factor of 2. This may indicate that at these larger radii either: i) the cluster SZ emission is contaminated by unresolved SZ sources along the line of sight; or ii) the pressure profile of Coma is higher at r > R 500 than the mean pressure profile predicted by the simulations used to constrain the models. The Planck image shows significant local steepening of the y profile in two regions about half a degree to the west and to the south-east of the cluster centre. These features are consistent with the presence of shock fronts at these radii, and indeed the western feature was previously noticed in the ROSAT PSPC mosaic as well as in the radio. Using Planck y profiles extracted from corresponding sectors we find pressure jumps of 4.9 +0.4 −0.2 and 5.0 +1.3 −0.1 in the west and south-east, respectively. Assuming Rankine-Hugoniot pressure jump conditions, we deduce that the shock waves should propagate with Mach number M w = 2.03 +0.09 −0.04 and M se = 2.05 +0.25 −0.02 in the west and south-east, respectively. Finally, we find that the y and radio-synchrotron signals are quasi-linearly correlated on Mpc scales, with small intrinsic scatter. This implies either that the energy density of cosmic-ray electrons is relatively constant throughout the cluster, or that the magnetic fields fall off much more slowly with radius than previously thought.