Dwarf galaxy planes: the discovery of symmetric structures in the Local Group

By M. Pawlowski, Pavel Kroupa, H. Jerjen. 2013

133 citations recorded by the source corpus.

Both major galaxies in the Local Group (LG) are surrounded by thin planes of mostly co-orbiting satellite galaxies, the vast polar structure (VPOS) around the Milky Way (MW) and the Great Plane of Andromeda (GPoA) around M31. We summarize the current knowledge concerning these structures and compare their relative orientations by re-determining their properties in a common coordinate system. The existence of similar, coherent structures around both major LG galaxies motivates an investigation of the distribution of the more distant non-satellite galaxies in the LG. This results in the discovery of two planes (diameters of 1–2Mpc) which contain almost all nearby non-satellite galaxies. The two LG planes are surprisingly symmetric. They are inclined by only 20 degrees relative to the galactic disc of M31, are similarly thin (heights of � 60kpc) and have near-to-identical offsets from the MW and from M31. They are inclined relative to each other by 35 degrees. Comparing the plane orientations with each other and with additional features reveals indications for an intimate connection between the VPOS and the GPoA. They are both polar with respect to the MW, have similar orbital directions and are inclined by about 45 ± 7 degrees relative to each other. The Magellanic Stream approximately aligns with the VPOS and the GPoA, but also shares its projected position and line-of-sight velocity trend with a part of the dominating structure of non-satellite dwarf galaxies. In addition, the recent proper motion measurement of M31 indicates a prograde orbit of the MW-M31 system, the VPOS and the GPoA. The alignment with other features such as the Supergalactic Plane and the over-density in hypervelocity stars are discussed as well. We end with a short summary of the currently proposed scenarios trying to explain the LG galaxy structures as either originating from cosmological structures or from tidal debris of a past galaxy encounter. We emphasise that there currently exists no full detailed model which satisfactorily explains the existence of the thin symmetric LG planes.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/fcd842ae30c32e1cf3acbc126d09e3a57f0ac40d

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Citations in the corpus

Galaxy Alignments: Observations and Impact on Cosmology (2015, background): “Pawlowski et al. (2013) have suggested that two similar structures can be found for non-satellite galaxies in the Local Group as a whole, at roughly equal distances to the Milky Way and M31.”
Co-orbiting satellite galaxy structures are still in conflict with the distribution of primordial dwarf galaxies (2014, methodology): “The positions and velocities of these objects are thereforeless reliable than those of galaxies embedded in resolved sub-haloes (W13,Pawlowski et al. 2013), but for simplicity and comparability to BB14, as well as W13 (see next Section) we do not discriminate between orphan and non-orphan galaxies.”
ETHOS - an effective theory of structure formation: dark matter physics as a possible explanation of the small-scale CDM problems (2015, background): “…related diversity of dwarf rotation curves (Oman et al. 2015), (iii) the corecusp (CC) problem for low surface brightness galaxies (De Blok & McGaugh 1997), and dwarf galaxies (e.g. see Oh et al. 2011; Walker & Peñarrubia 2011), and (iv) the plane of satellites problem (Pawlowski et al. 2013).”
Galaxies as simple dynamical systems: observational data disfavor dark matter and stochastic star formation (2014, background): “It will remain to be seen if the peculiar symmetric Local Group structure and the relative orientation of the VPOS and GPoA [175] as well as other dwarf galaxy arrangements nearby the Local Group [183] may follow naturally from a past encounter between the MW and Andromeda in SID [179].”