Intermediate Science Results Papers

1: Further validation of new Planck clusters with XMM-Newton

A galaxy cluster found by Planck

One of the clusters found by Planck, as seen in x-rays by XMM-Newton

Planck has found new candidates for massive galaxy clusters through the “Sunyaev-Zel'dovich effect”, but those candidates need to be followed up by other instruments in order to confirm that they are real and to measure their ages and distances. This paper presents X-ray observations of eleven candidates using ESA’s XMM-Newton X-ray satellite, and confirms that ten of the candidates are "bona fide clusters" that are very distant and very young - so distant that the light has taken billions of years to travel to Earth. It finds that the clusters are fainter in X-ray than would have been expected, and that many of them have a “disturbed morphology” - they are not simple, spherical clusters. New measurements with optical telescopes has also allowed the presents new distances previously-confirmed Planck clusters, and confirms that the distances calculated using both optical and X-rays are consistent with each other for a total of 20 clusters.

Corresponding author: Monique Arnaud (CEA, France)

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2: Comparison of Sunyaev–Zel'dovich measurements from Planck and from the Arcminute Microkelvin Imager for 11 galaxy clusters

Galaxy cluster Abell 1914 seen by Planck

An image of galaxy cluster Abell 1914, studied by Planck through the Sunyaev Zel'dovich effect

Observations of 11 galaxy clusters are shown using the Sunyaev-Zel'dovich effect, comparing measurements from Planck with those by the Arcminute Microkelvin Imager (AMI), a ground-based telescope array located near Cambridge, UK. The brightness and size of the clusters are measured from the AMI observations, and are found to be consistent with the Planck measurements for eight of the clusters - but with a tendency for AMI to find the Sunyaev-Zeldovich signal to be smaller in angular size and fainter than Planck. Significant discrepancies exist for the three remaining clusters in the sample. Simulations are used to show that the results from the two experiments are valid, and so the discrepancies are thought to arise from assumptions about the shape of the clusters, in particular the way in which the pressure of the hot gas in the cluster changes with radius from the centre. This implies that common assumptions about cluster shapes may not apply to all clusters.

Corresponding author: Michael Brown (University of Manchester, UK)

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3: The relation between galaxy cluster mass and Sunyaev-Zel'dovich signal

Abell2261 seen by XMM-Newton

Galaxy cluster Abell 2261, studied by Planck and XMM-Newton.

The masses of galaxy clusters can be measured by weak lensing -- the distortion of light from background galaxies due to the mass of the foreground galaxy cluster. The amount that the galaxies are lensed, or distorted, gives a measurement of the mass of the cluster. Nineteen Planck clusters were weighed in this way by previously-published observations from the Subaru Telescope. This paper compares the masses with the brightness of the clusters as seen by Planck, and finds that the measured relation agrees with previous similar comparisons. It also compares the mass estimated by weak lensing with that estimated from X-ray observations, and finds that the X-ray masses are around a quarter larger than the weak lensing masses. This is due to differences in the way that the concentration of the mass is measured (particularly for complicated clusters) and changes in the positions of the centre of the cluster between the different methods.

Corresponding author: Gabriel Pratt (CEA, France)

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4: The XMM-Newton validation programme for new Planck galaxy clusters

A pair of interacting galaxy clusters, discovered by Planck and seen here in x-rays by XMM-Newton

A pair of interacting galaxy clusters, discovered by Planck and seen here in x-rays by XMM-Newton

The final results are presented from the follow-up of new Planck cluster candidates with ESA’s XMM-Newton X-ray satellite, with 15 new Planck cluster candidates observed. Out of those, 14 new clusters were detected by XMM-Newton, 10 single clusters and 2 in double-cluster systems. Over the whole validation programme 51 new clusters were confirmed by XMM follow-up of Planck cluster candidates, including 4 double and 2 triple systems -- though some of these are chance projections on the sky of clusters at different distances. The paper also looks at the reliability of confirming candidates using the all-sky survey from the German ROSAT satellite, which was in orbit in the 1990s. That this works well for bright sources, but becomes less reliable for fainter sources - however most Planck clusters are present in the archival data. Compared to clusters selected from X-ray observations, the new SZ clusters from Planck are generally less bright than the average for clusters of the same mass.

 

Corresponding author: Jessica Democles (CEA, France)

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5: Pressure profiles of galaxy clusters from the Sunyaev-Zeldovich effect

The average density profile of galaxy clusters

The density of the gas in galaxy clusters if they are all put on top of each other, giving the average size and shape of them all.

Taking advantage of the all-sky coverage and broad frequency range of the Planck satellite, we study the Sunyaev-Zeldovich (SZ) effect of 62 nearby massive clusters detected in the 14-month nominal survey, along with the pressure profile of the hot gas in the cluster. Careful reconstruction of the SZ signal indicates that most clusters are individually detected, and by combining many measurements the average pressure profile can be extended further. This measurement of the pressure profile agrees with previous results from Planck and ESA’s XMM-Newton X-ray satellite. It also agrees with theoretical predictions, though at larger radii the average pressure profile is shallower than the predictions.

Corresponding author: Etienne Pontecouteau (IRAP, France)

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6: The dynamical structure of PLCKG214.6+37.0, a Planck discovered triple system of galaxy clusters

A triple galaxy cluster, seen by Planck

The first ever triple-cluster of galaxies, discovered by Planck through the Sunyaev-Zel'dovich effect

The survey of galaxy clusters performed by Planck through the Sunyaev-Zeldovich (SZ) effect has already discovered many interesting objects, thanks to the whole coverage of the sky. One of the SZ candidates detected in the early months of the mission near to the signal to noise threshold, which has catalogue name “PLCKG214.6+37.0”, was later revealed by ESA’s XMM-Newton x-ray satellite to be a triple system of galaxy clusters. We have further investigated this puzzling system at a wide range of wavelengths, and we present here the results from more sensitive XMM-Newton observations. The characterisation of the physical properties of the three components has allowed us to build a model of the system to better explain the Planck results. Using X-ray emission lines from iron, we measured the distance to the three separate clusters, and confirmed that the three clumps are likely part of the same supercluster structure. Measurements of the motions of the three clusters relative to one another suggests that we are witnessing the early stages in the formation of a massive cluster.

Corresponding author: Mariachiara Rossetti (University of Milan, Italy)

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7: Statistical properties of infrared and radio extragalactic sources from the Planck Early Release Compact Source Catalogue at frequencies between 100 and 857 GHz

The Planck point source catalogue

A map of many of the objects in the Planck Early Release Compact Source Catalogue

Planck released the Early Release Compact Source Catalogue in January 2011; this paper follows that by examining the sources that are brightest at higher frequencies (above 100GHz) The sources have been classified into galaxies dominated by thermal emission from dust, and those dominated by synchrotron emission from electrons in magnetic fields. The results provide more information on the general populations of these two types of sources.

Corresponding author: Hervé Dole (IAS, France)

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8: Filaments between interacting clusters

A filmanet between two galaxy clusters

One of the first filaments of hot gas between to massive galaxy clusters, detected by Planck through the Sunyaev Zel'dovich effect

About half of the baryons (particles such as protons and neutrons) in the Universe are expected to be found in filaments of hot, low density gas stretching between the galaxies. While most of these baryons remain undetected even by the most advanced X-ray observatories, the Planck satellite has provided hundreds of detections of the hot gas in clusters of galaxies via the Sunyaev-Zel'dovich (SZ) effect, and is an ideal instrument for studying the extended low density intergalactic medium. In this paper we use the Planck data to search for signatures of a fraction of these missing baryons between pairs of galaxy clusters, where the intergalactic medium is hotter and denser. For one merging cluster pair, we observe a significant SZ effect signal in the region between the clusters. By combining the Planck data with x-ray observations from the ROSAT satellite, we can constrain the temperature and density of this intercluster medium, providing the first SZ detection of the hot and diffuse intercluster gas. The temperature is found to be around 80 million degrees, and a density of around 370 particles per cubic metre.

Corresponding author: Guillaume Hurier (LPSC, France)

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9: Detection of the Galactic haze with Planck

The Galactic Haze

The "Galactic Haze" as seen by Planck

Using precise full-sky observations from Planck, and subtracting the emission from known sources, we identify and characterize the emission from the "Galactic Haze" at microwave wavelengths. The haze is a distinct component of diffuse Galactic emission, roughly centered on the Galactic centre, stretching around 35 degrees above and below the Galactic plane and around 15 degrees each way around the plane. By combining the Planck data with observations from the WMAP satellite we are able to rule out emission from hot gas, and favour synchrotron emission from unusually high energy electrons. There are also some similarities between the shape of the “haze” seen by Planck and the "bubbles” seen in gamma-rays by the Fermi satellite, indicating that we have a multi-wavelength view of a distinct component of our Galaxy. Given both the peculiarly high energy of the electrons, and the extended nature of the emission, it is highly unlikely that the haze electrons result from supernova shocks in the Galactic disk. Instead, a new mechanism for cosmic-ray acceleration in the centre of our Galaxy is implied.

Corresponding author: Krzysztof Gorski (JPL-Caltech, USA)

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10: Physics of the hot gas in the Coma cluster

The Coma cluster as seen by Planck

The Coma Cluster of galaxies, studied by Planck using the Sunyaev Zel'dovich effect.

We present an analysis of Planck satellite data on the Coma Cluster observed via the Sunyaev-Zel'dovich (SZ) effect. Planck is able to detect SZ emission out to a larger radius from the cluster centre than before. Previously proposed models for the distribution of hot gas in clusters do not agree with the observations, with Coma having more gas at larger radii than the simulations. The Planck data also shows significant jumps in the SZ signal 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. Finally, the agreement between SZ measurements and radio emission is used to constrain models of the electrons and magnetic fields in the Coma Cluster.

Corresponding author: Pasquale Mazzotta (University of Rome, Italy)

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