Planck's first glimpse at galaxy clusters and a new supercluster

Surveying the microwave sky, Planck is obtaining qualitatively new images of galaxy clusters, revealing one of them to be a previously unknown supercluster. Planck has provided by far most detailed images of clusters to date in the Sunyaev-Zel'dovich effect (SZE), a characteristic signature  which clusters imprint on the Cosmic Microwave Background (CMB). This effect was predicted in 1969 by Rashid Sunyaev, presently director at the Max Planck Institute for Astrophysics, and Yakov Zel'dovich.

Fig.: The gas of the Coma galaxy cluster as it appears through the Sunyaev-Zel'dovich Effect (colors) and in X-rays (contour lines).
Copyright: Planck image: ESA/ LFI & HFI Consortia;
ROSAT image: Max-Planck-Institut für extraterrestrische Physik; Acknowledgment: Davide De Martin (ESA/Hubble)

The SZE is the change of energy experienced by CMB photons as they pass through the hot gas atmospheres of galaxy clusters on their way to Earth. It imprints a characteristic signature on the CMB itself and is thus a unique tool for detecting galaxy clusters, even at high redshift. The nine frequency channels of Planck were carefully chosen with this particular phenomenon very much in mind.

Planck discovered the SZ signal from the previously unknown supercluster, which contains three clusters of galaxies. ESA's XMM-Newton telescope pointed in that direction, confirmed the presence of X-Rays from these three clusters of galaxies forming the supercluster. The SZ-signal has possibly an additional component from material betwen the clusters. This provides important clues about the distribution of gas on very large cosmic scales.

Planck's primary goal is to capture the most ancient light of the cosmos, the CMB. The satellite scans the sky in nine frequency channels spanning the spectral range from 30 to 857 GHz. Such a broad spectral coverage is not only critical for removing all sources of contamination from the CMB, in order to deliver what will be the sharpest image of the early Universe ever achieved - it also makes Planck an excellent hunter of galaxy clusters by means of the Sunyaev-Zel'dovich effect.

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