A dynamical model of the local cosmic expansion

Abstract

We combine the equations of motion that govern the dynamics of galaxies in the local volume with Bayesian techniques in order to fit orbits to published distances and velocities of galaxies within $\sim 3$ Mpc. We find a Local Group (LG) mass $2.3\pm 0.7\times 10^{12}{\mathrm{M}}_{\odot }$ that is consistent with the combined dynamical masses of M31 and the Milky Way, and a mass ratio $0.54_{-0.17}^{+0.23}$ that rules out models where our Galaxy is more massive than M31 with $\sim 95\%$ confidence. The Milky Way's circular velocity at the solar radius is relatively high, $245\pm 23$ km/s, which helps to reconcile the mass derived from the local Hubble flow with the larger value suggested by the `timing argument'. Adopting {\it Planck}'s bounds on ${\Omega }_{\Lambda }$ yields a (local) Hubble constant $H_0=67\pm 5$km/s/Mpc which is consistent with the value found on cosmological scales. Restricted N-body experiments show that substructures tend to fall onto the LG along the Milky Way-M31 axis, where the quadrupole attraction is maximum. Tests against mock data indicate that neglecting this effect slightly overestimates the LG mass without biasing the rest of model parameters. We also show that both the time-dependence of the LG potential and the cosmological constant have little impact on the observed local Hubble flow.

22 pages, 14 figures. Accepted to MNRAS. An error in the apex calculation (Appendix A) was found and has been fixed. The new constraints favour models where the Milky Way is less massive than M31. The rest of model parameters and conclusions remain unchanged

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Cited by in corpus (24)

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• A new look at microlensing limits on dark matter in the Galactic halo
• Calculation of the local density of relic neutrinos
• Dynamical evidence for a strong tidal interaction between the Milky Way and its satellite, Leo V
• The Role of Baryons in Creating Statistically Significant Planes of Satellites around Milky Way-Mass Galaxies
• Hubble tension vs two flows
• Solo dwarfs III: Exploring the orbital origins of isolated Local Group galaxies with Gaia Data Release 2
• HST Imaging of the Local Volume Dwarf Galaxies Pisces A&B: Prototypes for Local Group Dwarfs
• Cosmic flow around local massive galaxies
• Quantifying the Origin and Distribution of Intracluster Light in a Fornax-like Cluster
• Dwarfs in the Milky Way halo outer rim: first in-fall or backsplash satellites?
• Local Group Analogs in $\Lambda$CDM cosmological simulations
• Solo dwarfs IV: Comparing and contrasting satellite and isolated dwarf galaxies in the Local Group
• The Local Group as a test system for Modified Newtonian Dynamics
• Exploring the centre of mass properties of LG-like galaxies
• Dark matter effect attributed to the inherent structure of cosmic space
• An intriguing coincidence between the majority of vast polar structure dwarfs and a recent major merger at the M31 position
• Line-of-sight mass estimator and the masses of the Milky Way and Andromeda Galaxy
• Line-of-Sight Velocity Projection Impact on the Local Group Mass
• Timing Mass of the Local Group
• The mass distribution in and around the Local Group