On the coldness of the local Hubble flow: the role of baryons

TL;DR

This study uses cosmological simulations to assess whether baryons influence the coldness of the local Hubble flow, finding minimal differences between dark matter only and baryonic simulations on large scales.

Contribution

It demonstrates that baryonic physics has limited impact on the properties of the local Hubble flow compared to dark matter only models, validating the use of dark matter simulations for such studies.

Findings

Baryons do not significantly alter the spatial distribution of galaxies and dark matter haloes.

Velocity dispersion estimates are accurate within 3 km/s using dark matter simulations.

Mass estimates at the zero-velocity surface can be underestimated by at least 50%.

Abstract

(Abridged) Our aim is to investigate whether the presence of baryons can have any significant influence on the properties of the local Hubble flow which has proved to be "cold". We use two cosmological zoom simulations in the standard LCDM cosmology with the same set of initial conditions to study the formation of a local group-like system within a sphere of ~7 Mpc/h. The first one is a pure dark matter simulation (runDM) while a complete treatment of the physics of baryons is introduced in the second one (runB). We found that galaxies identified in runB and their corresponding dark matter haloes in runDM have very similar spatial distributions and dynamical properties on large scales. Then, when analyzing the velocity field and the deviation from a pure Hubble flow in both simulations, namely when computing the dispersion of peculiar velocities of galaxies \sigma*(R) and those of their corresponding dark matter haloes in runDM, we found no particular differences for distances R=1 to 8 Mpc from the local group mass center. The results indicate that the "true" \sigma*(R) values can be estimated from the pure dark matter simulation with a mean error of 3 km/s when dark matter haloes are selected with maximum circular velocities of Vc$\ge$30 km/s, corresponding to a population of dark matter haloes in runB that host galaxies. By investigating the properties of the Hubble flow at distances R~0.7 to 3 Mpc, we also found that the estimation of the total mass enclosed at the radius of the zero-velocity surface R0, using the spherical infall model adapted to LCDM, can be underestimated by at least 50%.