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A plane of high-velocity galaxies across the Local Group

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Date
01/2018
Author
Banik, Indranil
Zhao, Hongsheng
Keywords
Gravitation
Galaxy: disc
Galaxy: kinematics and dynamics
Galaxies: distances and redshifts
Local Group
Dark matter
QB Astronomy
QC Physics
Astronomy and Astrophysics
NDAS
BDC
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Abstract
We recently showed that several Local Group (LG) galaxies have much higher radial velocities (RVs) than predicted by a 3D dynamical model of the standard cosmological paradigm. Here, we show that six of these seven galaxies define a thin plane with root mean square thickness of only 101 kpc despite a widest extent of nearly 3 Mpc, much larger than the conventional virial radius of the Milky Way (MW) or M31. This plane passes within ∼70 kpc of the MW–M31 barycentre and is oriented so the MW–M31 line is inclined by 16° to it. We develop a toy model to constrain the scenario whereby a past MW–M31 flyby in Modified Newtonian Dynamics (MOND) forms tidal dwarf galaxies that settle into the recently discovered planes of satellites around the MW and M31. The scenario is viable only for a particular MW–M31 orbital plane. This roughly coincides with the plane of LG dwarfs with anomalously high RVs. Using a restricted N-body simulation of the LG in MOND, we show how the once fast-moving MW and M31 gravitationally slingshot test particles outwards at high speeds. The most distant such particles preferentially lie within the MW–M31 orbital plane, probably because the particles ending up with the highest RVs are those flung out almost parallel to the motion of the perturber. This suggests a dynamical reason for our finding of a similar trend in the real LG, something not easily explained as a chance alignment of galaxies with an isotropic or mildly flattened distribution (probability = 0.0015).
Citation
Banik , I & Zhao , H 2018 , ' A plane of high-velocity galaxies across the Local Group ' , Monthly Notices of the Royal Astronomical Society , vol. 473 , no. 3 , pp. 4033-4054 . https://doi.org/10.1093/mnras/stx2596
Publication
Monthly Notices of the Royal Astronomical Society
Status
Peer reviewed
DOI
https://doi.org/10.1093/mnras/stx2596
ISSN
0035-8711
Type
Journal article
Rights
© 2017, the Author(s). This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1093/mnras/stx2596
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  • University of St Andrews Research
URL
https://academic.oup.com/mnras/article/doi/10.1093/mnras/stx2596/4411820/A-Plane-of-High-Velocity-Galaxies-Across-the-Local?guestAccessKey=7a7e184a-6b06-4b64-901c-e0c2d07c9621
URI
http://hdl.handle.net/10023/11862

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