|Ph.D Student||Mikulizky Ziv|
|Subject||The Kinematics of the Local Group|
|Department||Department of Physics||Supervisor||Professor Adi Nusser|
|Full Thesis text|
The aim of this research is to use the comprehensive and accurate
present day observational data on positions, distances and
heliocentric radial velocities of galaxies, to study the kinematics of
the Local Group and the flow of nearby galaxies. The main goals are:
to place strong constraints on the properties of the local universe and
on the cosmological paradigm for structure formation; estimate the
amplitude of the Local Group bulk motion and study the coherence of
the local flow; estimate Hubble's constant at different volumes shells.
We achieve this using our own catalogue of galaxies within a radius
of 5 Mpc. This catalogue is the product of cross-referencing
observational data from various publicly available databases.
In this study the kinematic of the Local Group and nearby galaxies are
studied with respect to the Local Group rest frame. To obtain an
accurate transformation of the observed heliocentric radial velocities
to the Local Group rest frame we must start with a detailed study of
the Local Group.
The Local Group of galaxies is a dynamical gravitationally bound system.
It consists of our own galaxy, the Milky Way, with its satellite galaxies,
the Andromeda (M31) galaxy with its own satellites, and a handful of
``non-satellite'' galaxies, i.e. galaxies which are neither bound to
the Milky-Way or Andromeda. The transformation of the observed
heliocentric radial velocities to the Local Group rest frame requires
an accurate estimate of the solar motion in the Local Group rest frame.
This in turn demands an accurate sample of the ``non-satellite'' Local
Group members. We start by using the data in the literature to identify
what we call the well-established ``non-satellite'' members of the Local
Group. We then employ a physical criterion to assess the membership of
additional candidates. Once we have an accurate sample of the
``non-satellite'' members we use it to estimate the solar motion with
respect to the Local Group rest frame.
Using our estimate for the solar motion in the Local Group rest frame
we transform the observed heliocentric radial velocities to the Local
Group rest frame and plot the velocity maps for the Local Group and
We then propose two models for the flow of nearby galaxies. In the first
model the flow is modelled has a Hubble term (isotopic expansion) plus a
bulk motion term. In the second model, the Hubble term is replaced with a
symmetric tensor, which allows us to probe the expansion rate of the
universe at different directions. The free parameters of both of these
models are estimated at different volume shells. For the second model,
we also find the diagonalized form of the tensor.
The anisotropy in the spatial distribution of nearby galaxies together
with their law number, may bias our results. The robustness of our
results against biasing is verified by conducting bias tests on various
samples of mock catalogues.