Considerations on how to investigate planes of satellite galaxies

Abstract

The existence of a spatially thin, kinematically coherent Disk of Satellites (DoS) around the Milky Way (MW), is a problem that often garners vivacious debate in the literature or at scientific meetings. One of the most recent incarnations of this wrangle occurred with two papers by Maji et al, who argued that these structures "maybe a misinterpretation of the data". These claims are in stark contrast to previous works. Motivated by this and other recent publications on this problem, we discuss necessary considerations to make, observational effects to consider, and pitfalls to avoid when investigating satellite galaxy planes such as the MW's DoS. In particular, we emphasize that conclusions need to have a statistical basis including a determination of the significance of satellite alignments, observational biases must not be ignored, and measurement errors (e.g. for proper motions) need to be considered. We discuss general problems faced by attempts to determine the dynamical stability of the DoS via orbit integrations of MW satellite galaxies, and demonstrate that to interpret simulations, it is helpful to compare them with a null case of isotropically distributed satellite positions and velocities. Based on these criteria, we find that the conclusions of Maji et al. do not hold up to scrutiny, and that their hydrodynamic cosmological simulation of a single host shows no evidence for a significant kinematic coherence among the simulated satellite galaxies, in contrast to the observed MW system.

8 pages, 3 figures. Accepted for publication in Astronomische Nachrichten / Astronomical Notes

References in corpus (19)

• A Vast Thin Plane of Co-rotating Dwarf Galaxies Orbiting the Andromeda Galaxy
• Hundreds of Milky Way Satellites? Luminosity Bias in the Satellite Luminosity Function
• One Law To Rule Them All: The Radial Acceleration Relation of Galaxies
• Not so lumpy after all: modeling the depletion of dark matter subhalos by Milky Way-like galaxies
• "Skinny Milky Way, Please", says Sagittarius
• The Origin of the Bifurcation in the Sagittarius Stream
• Globular Cluster Streams as Galactic High-Precision Scales - The Poster Child Palomar 5
• Co-orbiting satellite galaxy structures are still in conflict with the distribution of primordial dwarf galaxies
• Two Planes of Satellites in the Centaurus A Group
• Velocity anti-correlation of diametrically opposed galaxy satellites in the low redshift universe
• Discs of Satellites: the new dwarf spheroidals
• Reproducing properties of MW dSphs as descendants of DM-free TDGs
• Testing the two planes of satellites in the Centaurus Group
• The Role of Baryons in Creating Statistically Significant Planes of Satellites around Milky Way-Mass Galaxies
• Co-orbiting planes of sub-halos are similarly unlikely around paired and isolated hosts
• Proper Motion of the Leo II Dwarf Galaxy Based On Hubble Space Telescope Imaging
• On the Stability of Satellite Planes I: Effects of Mass, Velocity, Halo Shape and Alignment
• Proper Motion of the Draco Dwarf Galaxy Based On Hubble Space Telescope Imaging
• The potential role of NGC 205 in generating Andromeda's vast thin co-rotating plane of satellite galaxies

Cited by in corpus (17)

• The Planes of Satellite Galaxies Problem, Suggested Solutions, and Open Questions
• The Milky Way's Disk of Classical Satellite Galaxies in Light of Gaia DR2
• Dark matters on the scale of galaxies
• Planes of satellites around Milky Way/M31-mass galaxies in the FIRE simulations and comparisons with the Local Group
• MOND simulation suggests the origin of some peculiarities in the Local Group
• Origin of the Local Group satellite planes
• Evolution of galactic planes of satellites in the EAGLE simulation
• The Pristine Dwarf-Galaxy survey - II. In-depth observational study of the faint Milky Way satellite Sagittarius II
• The Lopsidedness of Satellite Galaxy Systems in $\Lambda$CDM simulations
• 3D hydrodynamic simulations for the formation of the Local Group satellite planes
• On the Co-Orbitation of Satellite Galaxies Along the Great Plane of Andromeda: NGC 147, NGC 185, and Expectations from Cosmological Simulations
• Galactic forces rule dynamics of Milky Way dwarf galaxies
• We are not the 99 percent: quantifying asphericity in the distribution of Local Group satellites
• The spatial distribution of satellites in galaxy clusters
• Andromeda's asymmetric satellite system as a challenge to cold dark matter cosmology
• Dark sector domain walls could explain the observed planes of satellites
• Testing a proposed "planarity" tool for studying satellite systems: On the alleged consistency of Milky Way satellite galaxy planes with $\Lambda$CDM