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Title: Planes of satellite galaxies and the cosmic web
Author: Noam I Libeskind, Yehuda Hoffman, R. Brent Tully, Helene M Courtois, Daniel Pomarede, Stefan Gottloeber, Matthias Steinmetz

Recent observational studies have demonstrated that most satellite galaxies tend to orbit their hosts on highly flattened, vast, possibly co-rotating planes. Two nearly parallel planes of satellites have been confirmed around the M31 galaxy and around the Centaurus A galaxy, while the Milky Way also sports a plane of satellites. It has been argued that such an alignment of satellites on vast planes is unexpected in the standard (LambdaCDM) model of cosmology if not even in contradiction to its generic predictions. Guided by LambdaCDM numerical simulations, which suggest that satellites are channeled towards hosts along the axis of the slowest collapse as dictated by the ambient velocity shear tensor, we re-examine the planes of local satellites systems within the framework of the local shear tensor derived from the Cosmicflows-2 dataset. The analysis reveals that the Local Group and Centaurus A reside in a filament stretched by the Virgo cluster and compressed by the expansion of the Local Void. Four out of five thin planes of satellite galaxies are indeed closely aligned with the axis of compression induced by the Local Void. Being the less massive system, the moderate misalignment of the Milky Way's satellite plane can likely be ascribed to its greater susceptibility to tidal torques, as suggested by numerical simulations. The alignment of satellite systems in the local universe with the ambient shear field is thus in agreement with predictions of the LambdaCDM model.

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Studie stürzt Standardtheorie der Kosmologie in die Krise
Neue Erkenntnisse zu Satellitengalaxien der MilchstraBe

Muss Newtons Gravitationstheorie abgeändert werden, weil sie zur Erklärung mancher Beobachtungen nicht taugt? Inzwischen mehren sich die Stimmen, die diese ketzerische These unterstützen. Zwei neue Studien zu den so genannten Satellitengalaxien in der Peripherie der MilchstraBe dürften ihr nun weiteren Auftrieb geben. Durchgeführt wurden sie von Physikern der Universität Bonn zusammen mit Kollegen aus Osterreich und Australien. Ihre Ergebnisse könnten das Theorie-Gebäude der Standardphysik ins Wanken bringen.

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Title: The Orbital Distribution of Satellite Galaxies
Authors: Stéphane Herbert-Fort, Dennis Zaritsky, Yeun Jin Kim, Jeremy Bailin, James E. Taylor

We measure the distribution of velocities for prograde and retrograde satellite galaxies using a combination of published data and new observations for 78 satellites of 63 extremely isolated disc galaxies (169 satellites total). We find that the velocity distribution is non-Gaussian (>99.9% confidence), but that it can be described as the sum of two Gaussians, one of which is broad (sigma = 176 ±15 km/s), has a mean prograde velocity of 86 ±30 km/s, and contains ~55% of the satellites, while the other is slightly retrograde with a mean velocity of -21 ±22 km/s and sigma = 74 ±18 km/s and contains ~45% of the satellites. Both of these components are present over all projected radii and found in the sample regardless of cuts on primary inclination or satellite disc angle. The double-Gaussian shape, however, becomes more pronounced among satellites of more luminous primaries. We remove the potential dependence of satellite velocity on primary luminosity using the Tully-Fisher relation and still find the velocity distribution to be asymmetric and even more significantly non-Gaussian. The asymmetric velocity distribution demonstrates a connection between the inner, visible disc galaxy and the kinematics of the outer, dark halo. The reach of this connection, extending even beyond the virial radii, suggests that it is imprinted by the satellite infall pattern and large-scale effects, rather than by higher-level dynamical processes in the formation of the central galaxy or late-term evolution of the satellites.

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