The European Space Agency's Planck satellite, which is dedicated to studying the early Universe and its subsequent evolution, was launched on 14 May 2009. It scanned the microwave and submillimetre sky continuously between 12 August 2009 and 23 October 2013. In February 2015, ESA and the Planck Collaboration released the second set of cosmology products based on data from the entire Planck mission, including both temperature and polarization, along with a set of scientific and technical papers and a web-based explanatory supplement. This paper gives an overview of the main characteristics of the data and the data products in the release, as well as the associated cosmological and astrophysical science results and papers. The data products include maps of the cosmic microwave background (CMB), the thermal Sunyaev-Zeldovich effect, diffuse foregrounds in temperature and polarization, catalogues of compact Galactic and extragalactic sources (including separate catalogues of Corresponding author: C. R. Lawrence, e-mail: charles.lawrence@jpl.nasa.govArticle published by EDP Sciences A1, page 1 of 38 A&A 594, A1 (2016) Sunyaev-Zeldovich clusters and Galactic cold clumps), and extensive simulations of signals and noise used in assessing uncertainties and the performance of the analysis methods. The likelihood code used to assess cosmological models against the Planck data is described, along with a CMB lensing likelihood. Scientific results include cosmological parameters derived from CMB power spectra, gravitational lensing, and cluster counts, as well as constraints on inflation, non-Gaussianity, primordial magnetic fields, dark energy, and modified gravity, and new results on low-frequency Galactic foregrounds.

We used data from the WMAP satellite at 23, 33 and 41 GHz to study the diffuse polarised emission over the entire sky. The emission originates mostly from filamentary structures with well-ordered magnetic fields. Some of these structures have been known for decades in radio continuum maps. Their origin is not clear and there are many filaments that are visible for the first time. We have identified and studied 11 filaments. The polarisation fraction of some of them can be as high as 40%, which is a signature of a well ordered magnetic field. The polarisation spectral indices, averaged over 18 regions in the sky is β = −3.06 ± 0.02, consistent with synchrotron radiation. There are significant variations in β over the sky (∆β ≈ 0.2).We explore the link between the large-scale filaments and the local ISM, using the model of an expanding shell in the solar vicinity. We compared observed polarisation angles with the predictions from the model and found good agreement. This strongly suggests that many large scale filaments and loops are nearby structures. This is important in the context of the Galactic magnetic field as these structures are normally included in global models, neglecting the fact that they might be local. We also studied the level of contamination added by the diffuse filaments to the CMB polarisation power spectra. We conclude that, even though these filaments present low radio brightness, a careful removal will be necessary for future all-sky CMB polarisation analysis.

Anomalous Microwave Emission (AME) is a component of diffuse Galactic radiation observed at frequencies in the range ≈ 10-60 GHz. AME was first detected in 1996 and recognised as an additional component of emission in 1997. Since then, AME has been observed by a range of experiments and in a variety of environments. AME is spatially correlated with far-IR thermal dust emission but cannot be explained by synchrotron or free-free emission mechanisms, and is far in excess of the emission contributed by thermal dust emission with the power-law opacity consistent with the observed emission at sub-mm wavelengths. Polarization observations have shown that AME is very weakly polarized ( 1 %). The most natural explanation for AME is rotational emission from ultra-small dust grains ("spinning dust"), first postulated in 1957.

Quasar absorption line systems are redshift-independent sensitive mass tracers. Here we describe the first optical survey of absorption systems associated with galaxy clusters at z = 0.3 − 0.9. We have cross-correlated quasars from the third data release of the Sloan Digital Sky Survey with high-redshift cluster/group candidates from the Red-Sequence Cluster Survey. In a common field of ≈ 20 square degrees, we have found 442 quasar-cluster pairs for which the Mg II λλ2796, 2803Å doublet might be detected at a transverse (physical) distance < 2 h −1 71 Mpc from the cluster centers. In addition, we have found 33 other pairs in the literature and we have discovered 7 new quasars with foreground clusters. To investigate the incidence (dN/dz) and equivalent-width distribution n(W ) of Mg II systems at cluster redshifts, two statistical samples were drawn out of these pairs: one made of high-resolution spectroscopic quasar observations (46 pairs), and one made of quasars used in Mg II searches found in the literature (375 pairs). The total redshift path from an ad-hoc definition of 'cluster redshift path' is ∆z cluster = 6.3 and ∆z cluster = 57.0 for the two samples, respectively. We estimate the completeness level to be nearly 100 % for W detection thresholds of W 2796 0 > 0.05 and W 2796 0 > 1.0Å in the two samples, respectively. The results are: (1) the population of strong Mg II systems (W 2796 0 > 2.0Å) near cluster redshifts shows a significant (> 3σ) overabundance (up to a factor of 15) when compared with the 'field' population; (2) the overabundance is more evident at smaller distances (d < 1 h −1 71 Mpc) than larger distances (d < 2 h −1 71Mpc) from the cluster center; and, (3) the population of weak Mg II systems (W 2796 0 < 0.3Å) near cluster redshifts conform to the field statistics. Unlike in the field, this dichotomy makes n(W ) in clusters appear flat and well fitted by a power-law in the entire W -range. We assess carefully all possible selection and systematic effects, and conclude that the signal is indeed due to the presence of clusters. In particular, a sub-sample of the most massive clusters yields a stronger and still significant signal. Since either the absorber number density or fillingfactor/cross-section affects the absorber statistics, an interesting possibility is that we have detected the signature of truncated halos due to environmental effects. Thus, we argue that the excess of strong systems is due to a population of absorbers in an overdense galaxy environment, and the lack of weak systems to a different population, that got destroyed in the cluster environment.Finally, comparison with models of galaxy counts show that there is proportionally less cold gas in more massive clusters than in low-mass systems, and two orders of magnitude less Mg II cross-section due to weak systems than due to stronger systems. Zibetti et al. 2007) for which extensive field surveys exist. The Mg II doublet has been used extensively in spectroscopic quasar surveys because it is a strong and an easy-to-find t...

Anomalous microwave emission (AME) has been previously studied in two well-known molecular clouds and is thought to be due to electric dipole radiation from small spinning dust grains. It is important to measure the polarization properties of this radiation both for component separation in future cosmic microwave background (CMB) experiments and also to constrain dust models. We have searched for linearly polarized radio emission associated with the ρ Ophiuchi and Perseus molecular clouds using WMAP 7-year data. We found no significant polarization within an aperture of 2 • diameter. The upper limits on the fractional polarization of spinning dust in the ρ Ophiuchi cloud are 1.7, 1.6 and 2.6 per cent (at 95 per cent confidence level) at K, Ka and Q bands, respectively. In the Perseus cloud we derived upper limits of 1.4, 1.9 and 4.7 per cent, at K, Ka and Q bands, respectively; these are similar to those found by López-Caraballo et al. If AME at high Galactic latitudes has a similarly low level of polarization, this will simplify component separation for CMB polarization measurements. We can also rule out single domain magnetic dipole radiation as the dominant emission mechanism for the 20-40 GHz. The polarization levels are consistent with spinning dust models.