How Close Dark Matter Halos and MOND Are to Each Other: Three-Dimensional Tests Based on Gaia DR2

Abstract

Aiming at discriminating different gravitational potential models of the Milky Way, we perform tests based on the kinematic data powered by the Gaia DR2 astrometry, over a large range of $(R,z)$ locations. Invoking the complete form of Jeans equations that admit three integrals of motion, we use the independent $R$- and $z$-directional equations as two discriminators ($T_R$ and $T_z$). We apply the formula for spatial distributions of radial and vertical velocity dispersions proposed by Binney et al., and successfully extend it to azimuthal components, ${\sigma }_{\theta }(R,z)$ and $V_{\theta }(R,z)$; the analytic form avoids the numerical artifacts caused by numerical differentiation in Jeans-equations calculation given the limited spatial resolutions of observations, and more importantly reduces the impact of kinematic substructures in the Galactic disk. It turns out that whereas the current kinematic data are able to reject Moffat's Modified Gravity (let alone the Newtonian baryon-only model), Milgrom's MOND is still not rejected. In fact, both the carefully calibrated fiducial model invoking a spherical dark matter (DM) halo and MOND are equally consistent with the data at almost all spatial locations (except that probably both have respective problems at low-$|z|$ locations), no matter which a tracer population or which a meaningful density profile is used. Because there is no free parameter at all in the quasi-linear MOND model we use, and the baryonic parameters are actually fine-tuned in the DM context, such an effective equivalence is surprising, and might be calling forth a transcending synthesis of the two paradigms.

20 pages, 13 figures; accepted for publication in MNRAS

References in corpus (13)

• Dark Matter Candidates from Particle Physics and Methods of Detection
• The mass distribution and gravitational potential of the Milky Way
• The Radial Acceleration Relation in Rotationally Supported Galaxies
• The Local Dark Matter Density
• Constraining the Galaxy's dark halo with RAVE stars
• From galactic bars to the Hubble tension: weighing up the astrophysical evidence for Milgromian gravity
• Milky Way potentials in CDM and MOND. Is the Large Magellanic Cloud on a bound orbit?
• Vertical dynamics of disk galaxies in MOND
• Mapping the Galactic disk with the LAMOST and Gaia Red clump sample: I: precise distances, masses, ages and 3D velocities of $\sim$ 140000 red clump stars
• Milky Way total Mass derived by Rotation Curve and Globular Cluster kinematics from Gaia EDR3
• Models of modified-inertia formulation of MOND
• $\text{galkin}$: a new compilation of the Milky Way rotation curve data
• Understanding the internal dynamics of elliptical galaxies without non-baryonic dark matter

Cited by in corpus (8)

• Strong constraints on the gravitational law from $Gaia$ DR3 wide binaries
• Internal kinematics of GAIA DR3 wide binaries: anomalous behaviour in the low acceleration regime
• Hydrodynamical structure formation in Milgromian cosmology
• A new scale in the quasi-static limit of Aether Scalar Tensor Theory
• The dark side of early galaxies: $\text{geko}$ uncovers dark-matter fractions at $z\sim 4-6$
• Dynamical friction in the quasi-linear formulation of modified Newtonian dynamics (QuMOND)
• The modified Newtonian dynamics with an extra anti-dissipation term can yield the MOND model
• Testing MOND using the dynamics of nearby stellar streams