English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We study the correlation of orbital poles of the 11 classical satellitegalaxies of the Milky Way, comparing results from previous proper motions withthe independent data by Gaia DR2. Previous results on the degree of correlationand its significance are confirmed by the new data. A majority of thesatellites co-orbit along the Vast Polar Structure, the plane (or disk) ofsatellite galaxies defined by their positions. The orbital planes of eightsatellites align to $<20^\circ$ with a common direction, seven even orbit inthe same sense. Most also share similar specific angular momenta, though theirwide distribution on the sky does not support a recent group infall orsatellites-of-satellites origin. The orbital pole concentration hascontinuously increased as more precise proper motions were measured, asexpected if the underlying distribution shows true correlation that is washedout by observational uncertainties. The orbital poles of the up to seven mostcorrelated satellites are in fact almost as concentrated as expected for thebest-possible orbital alignment achievable given the satellite positions.Combining the best-available proper motions substantially increases the tensionwith $\Lambda$CDM cosmological expectations: <0.1 per cent of simulatedsatellite systems in IllustrisTNG contain seven orbital poles as closelyaligned as observed. Simulated systems that simultaneously reproduce theconcentration of orbital poles and the flattening of the satellite distributionhave a frequency of <0.1 per cent for any number of k > 3 combined orbitalpoles, indicating that these results are not affected by a look-elsewhereeffect. This compounds the Planes of Satellite Galaxies Problem.

The Milky Way's Disk of Classical Satellite Galaxies in Light of Gaia DR2