טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentMikulizky Ziv
SubjectThe Kinematics of the Local Group
DepartmentDepartment of Physics
Supervisor Professor Adi Nusser
Full Thesis textFull thesis text - English Version


Abstract

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

nearby galaxies.

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.