Motion of the Local Group as a cosmological probe
  In this thesis, we use the motion of the Local Group of galaxies (LG) through
the Universe to measure the cosmological parameter of non-relativistic matter
density, Omega_m. For that purpose, we compare the peculiar velocity of the LG
with its gravitational acceleration. The former is known from the dipole of the
cosmic microwave background radiation and the latter is estimated here from the
clustering dipole of galaxies in the Two Micron All Sky Survey (2MASS) Extended
Source Catalog. We start by presenting the general framework of perturbation
theory of gravitational instability in the expanding Universe and how it
applies to the peculiar motion of the LG. Next, we study a particular effect
for the dipole measurement, related to the fact that a nearby Local Void is
partially hidden behind our Galaxy. We then describe in detail how we handled
the 2MASS extragalactic data for the purpose of our analysis. Finally, we
present two methods to estimate the density Omega_m, combined with the linear
biasing b into the parameter beta = (Omega_m)^{0.55} / b, from the comparison
of the LG velocity and acceleration. The first approach is to study the growth
of the 2MASS clustering dipole with increased depth of the sample and compare
it with theoretical expectations. The second is to apply the maximum-likelihood
method in order to improve the precision of the measurement. With both these
methods we find beta=0.4 and Omega_m=0.2, which is consistent with various
independent estimates. We also briefly mention some future prospects in the
field.
