On the coldness of the local Hubble flow: the role of baryons
  (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%.
