The VPOS: a vast polar structure of satellite galaxies, globular clusters and streams around the Milky Way

By M. Pawlowski, J. Pflamm-Altenburg, Pavel Kroupa. 2012

265 citations recorded by the source corpus.

It has been known for a long time that the satellite galaxies of the Milky Way (MW) show a significant amount of phase-space correlation, they are distributed in a highly inclined Disc of Satellites (DoS). We have extended the previous studies on the DoS by analysing for the first time the orientations of streams of stars and gas, and the distributions of globular clusters within the halo of the MW. It is shown that the spatial distribution of MW globular clusters classified as young halo clusters (YH GC) is very similar to the DoS, while 7 of the 14 analysed streams align with the DoS. The probability to find the observed clustering of streams is only 0.3 per cent when assuming isotropy. The MW thus is surrounded by a vast polar structure (VPOS) of subsystems (satellite galaxies, globular clusters and streams), spreading from Galactocentric distances as small as 10 kpc out to 250 kpc. These findings demonstrate that a near-isotropic infall of cosmological sub-structure components onto the MW is essentially ruled out because a large number of infalling objects would have had to be highly correlated, to a degree not natural for dark matter sub-structures. The majority of satellites, streams and YH GCs had to be formed as a correlated population. This is possible in tidal tails consisting of material expelled from interacting galaxies. We discuss the tidal scenario for the formation of the VPOS, including successes and possible challenges. The potential consequences of the MW satellites being tidal dwarf galaxies are severe. If all the satellite galaxies and YH GCs have been formed in an encounter between the young MW and another gas-rich galaxy about 10-11 Gyr ago, then the MW does not have any luminous dark-matter substructures and the missing satellites problem becomes a catastrophic failure of the standard cosmological model.

Subfields: Astronomy and Astrophysics, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/52a62fb75ca15886b03c14952a78dfd653412b7c

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Statistical and Nonlinear Physics

Citations in the corpus

The SAGA Survey. I. Satellite Galaxy Populations around Eight Milky Way Analogs (2017, background): “In addition, studies have suggested that the satellites in the Milky Way exist in a co-rotating, planelike structure (Pawlowski et al. 2012), and similar structures are also found in the satellite systems of M31 (Ibata et al. 2013).”
Galaxies as simple dynamical systems: observational data disfavor dark matter and stochastic star formation (2014, background): “These tools have been tested carefully and proven to be ideal for robustly determining the significance of satellite anisotropies given their three-dimensional spatial information [8,85].”
Galaxy Alignments: An Overview (2015, background): “Lynden-Bell (1976) pointed out that this effect is also present in the Milky Way whose satellites and distant globular clusters lie in a tight plane within about 10◦ from the Galactic poles.”
Gaia DR2 proper motions of dwarf galaxies within 420 kpc (2018, background): “3 we plot an all-sky view of the orbital poles of the objects in the sample, concentrating on those within 200 kpc, and comparing their location on this plane with the vast polar structure (VPOS) of satellites (Pawlowski et al. 2012).”
Stellar Streams Discovered in the Dark Energy Survey (2018, background): “We do not find any strong association of stream poles coinciding with the proposed Vast Polar Structure (VPOS; Pawlowski et al. 2012, 2015).”
Modified Newtonian Dynamics (MOND): Observational Phenomenology and Relativistic Extensions (2011, background): “Young halo globular clusters define the same disk, and streams of stars and gas, tracing the orbits of the objects from which they are stripped, preferentially lie in this disk, too [347].”
Theory of dark matter superfluidity (2015, result): “13 • Vast planar structures and tidal dwarfs: The vast planar structures seen in the Local Group [17–23] and beyond [24] find a possible explanation in our scenario, similar to that proposed in MOND [18].”
Dwarf galaxy planes: the discovery of symmetric structures in the Local Group (2013, methodology): “The similar size between the filaments and the host galaxy haloes therefore results in a near-isotropic accretion of dark matter subhaloes onto host haloes (Lovell et al. 2011; Pawlowski et al. 2012b).”
EIGHT NEW MILKY WAY COMPANIONS DISCOVERED IN FIRST-YEAR DARK ENERGY SURVEY DATA (2015, background): “The thickness of the vast polar structure defined by Pawlowski et al. (2012) is 29 kpc, and we find that the DES satellites have a dispersion of ~28 kpc from this plane.”
CONFIRMATION OF FAINT DWARF GALAXIES IN THE M81 GROUP (2013, background): “Meanwhile most of the early type companions to the Milky Way appear to lie in a plane (Lynden-Bell 1976; Metz et al. 2008; Pawlowski et al. 2012).”
Co-orbiting satellite galaxy structures are still in conflict with the distribution of primordial dwarf galaxies (2014, methodology): “However, the nonisotropy of the simulated satellite systems is generally insufficient to explain the strong observed coherence of the satellite galaxy positions and velocities (e.g. Pawlowski et al. 2012).”
Milky Way Satellite Census. I. The Observational Selection Function for Milky Way Satellites in DES Y3 and Pan-STARRS DR1 (2019, background): “…made the simplifying assumption that the satellite population is isotropic, while observations suggest that this is very unlikely to be true for the Milky Way (e.g., Pawlowski et al. 2012; Koposov et al. 2015; Bechtol et al. 2015; Drlica-Wagner et al. 2015) and Andromeda (e.g., Ibata et al. 2013).”
Small scale problems of the $\Lambda$CDM model: a short review (2016, result): “[105] showed a disagreement with those of observations.”