Locally Cold Flows from Large-Scale Structure

Abstract

We show that the "cold" Hubble flow observed for galaxies around the Milky Way does not represent a problem in cosmology but is due to the particular geometry and dynamics of our local wall. The behavior of the perturbed Hubble flow around the Milky Way is the result of two main factors: at small scales (R < 1 Mpc) the inflow is dominated by the gravitational influence of the Milky Way. At large scales (R > 1 Mpc) the out flow reflects the expansion of our local wall which "cools down" the peculiar velocities. This is an intrinsic property of walls and is independent of cosmology. We find the dispersion of the local Hubble flow (1 < R < 3 Mpc) around simulated "Milky Way" haloes located at the centre of low-density cosmological walls to be σ_H ~ 30 km/s, in excellent agreement with observations. The expansion of our local wall is also reflected in the value of the measured local Hubble constant. For "Milky Way" haloes inside walls, we find super-Hubble flows with h_local \simeq 0.77 - 1.13. The radius of equilibrium (R_0) depends not only on the mass of the central halo and the Hubble expansion but also on the dynamics given by the local LSS geometry. The super-Hubble flow inside our local wall has the effect of reducing the radius at which the local expansion balances the gravitational influence of the Milky Way. By ignoring the dynamical effect of the local wall, the mass of the Milky Way estimated from R_0 can be underestimated by as much as ~ 30%.

5 pages, 3 figures, Submitted to MNRAS

Cited by in corpus (15)

• From galactic bars to the Hubble tension: weighing up the astrophysical evidence for Milgromian gravity
• The Hierarchical Structure and Dynamics of Voids
• A dynamical model of the local cosmic expansion
• Milky Way mass constraints from the Galactic satellite gap
• On the mass of the Local Group
• Origin of the Local Group satellite planes
• A Plane of High Velocity Galaxies Across the Local Group
• Large-Scale Velocity Dispersion and the Cosmic Web
• Intergalactic filaments spin
• Dynamical History of the Local Group in $\Lambda$CDM
• The Local Group in the cosmic web
• The MIP Ensemble Simulation: Local Ensemble Statistics in the Cosmic Web
• Dark energy domination in the local flow of giant galaxies
• The Unusual Milky Way-Local Sheet System: Implications for Spin Strength and Alignment
• On the absence of backsplash analogues to NGC 3109 in the $\Lambda$CDM framework