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 3 Mpc. We find a Local Group (LG) mass 2.3 ± 0.7 × 10^{12} M_{⊙} that is consistent with the combined dynamical masses of M31 and the Milky Way, and a mass ratio 0.54^{+0.23}_{0.17} that rules out models where our Galaxy is more massive than M31 with ∼95 per cent confidence. The Milky Way's circular velocity at the solar radius is relatively high, 245 ± 23 km s^{1}, which helps to reconcile the mass derived from the local Hubble flow with the larger value suggested by the `timing argument'. Adopting Planck's bounds on Ω_{Λ} yields a (local) Hubble constant H_{0} = 67 ± 5 km s^{1} Mpc^{1} which is consistent with the value found on cosmological scales. Restricted Nbody experiments show that substructures tend to fall on to the LG along the Milky WayM31 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.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 September 2014
 DOI:
 10.1093/mnras/stu879
 arXiv:
 arXiv:1405.0306
 Bibcode:
 2014MNRAS.443.2204P
 Keywords:

 Galaxy: fundamental parameters;
 Galaxy: kinematics and dynamics;
 Local Group;
 cosmological parameters;
 dark energy;
 dark matter;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 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