The study of cosmological radio backgrounds with the Sunyaev-Zel'dovich effect
Date
2017
Authors
Emritte, Mohammad Shehzad
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Abstract
According to the standard model of cosmology, the Universe has evolved from a thermal bath
of elementary particles and photons towards one comprising of collapsed structures such as
stars, galaxies and clusters of galaxies. The Cosmic Microwave Background (CMB) spectrum
and its angular anisotropy across the sky contain information on the physical processes,
matter distribution and evolution of the Universe across cosmic time. Primordial spectral
distortions of the CMB and its anisotropy can be studied through the inverse comptonization
process occuring in cosmic structures, known as the Sunyaev-Zel'dovich e ect (SZE). This
present study demonstrates how the SZE can be used to obtain information on the 21
cm background produced between the Dark Ages (DA) and the Epoch of Reionization
(EoR), on Non-Planckian (NP) modi cations of the CMB due to plasma frequency at the
recombination epoch, and on the anisotropy of the CMB at cluster locations, through the
study of the polarization of the SZE. To these aims, a full relativistic approach is employed,
that allows us to calculate the spectra of the SZE and its polarization component with high
precision, and allows to calculate it for any kind of electron population (thermal or nonthermal
plasma), and for an input spectrum that can deviate from the standard black-body
spectrum.
The SZE-21cm, which is the comptonized spectrum of the modi ed CMB due to physical
processes occuring during the DA and the EoR, is calculated for four models of the 21-cm
background. A full spectral analysis of the signal is performed and the importance of
relativistic e ects are highlighted. The results demonstrate that relativistic e ects are nonzero
over the entire frequency spectrum and hence cannot be ignored, particularly for hot
clusters. It is found that the amplitude of the SZE-21cm signal is of the order of Jy and
is within the reach of the SKA instrument. Clusters with high temperature and optical
depth are optimal targets to search for the SZE-21cm signal. The SKA can measure the
signal in the frequency interval 75-90 MHz for clusters with temperature higher than 5 keV.
Discerning the SZE-21cm from the standard SZE can be achieved using the SKA depending
on the 21-cm background model for temperatures > 10 keV.
Using CMB spectral data at both low and high frequencies, upper limits (206, 346 and
418 MHz at 1, 2, 3 con dence level) are placed on NP e ects associated with a non-zero
plasma frequency at the recombination epoch. The SZENP is derived for a CMB spectrum
modi ed due to plasma e ects using these upperlimits and a unique spectral feature is
obtained. A peak occures at the plasma frequency in the SZENP independent of cluster
parameters and the possibility of measuring the plasma frequency with the SKA and eVLA
is shown. Plasma e ects are also investigated on the spectrum of the cosmological 21-cm
background and it is found that such an e ect is important to consider when recovering the
history of the Universe during these epochs.
Polarization is a natural outcome of inverse Compton (IC) scattering and the anisotropy
of the CMB plays a big role in the production of polarization in Comptonization process.
The SZE polarization associated with the anisotropy of the CMB is derived in the full relativistic
regime for any general electron distribution. The spectral shapes of the Stokes
parameters induced by the IC scattering of the multipoles of the CMB for thermal and
non-thermal electrons are derived, focusing mainly on the quadrupole and octupole which
provide the largest possible detectable signals in cosmic structures. Our results demonstrate
the implication of relativistic e ects, which become important for high temperature
or non-thermal cluster environments. When relativistic e ects are accounted for, all the
multipoles of the CMB are involved in the production of polarization. The octupole induced
polarization spectrum reveals the existence of a cross-over frequency which is dependent
on cluster parameters such as temperature, minimum momentum and spectral index. The
possibilities to disentangle the quadrupole spectrum from the octupole one are discussed,
which would allow the measurments of these multipoles at cluster locations. The generality
of our approach allows us to calculate the SZE polarization spectra of the Bullet cluster
using multifrequency SZE data in intensity and compare the results with the sensitivities of
the SKA, ALMA, Millimetron and CORE++ instruments.
Although the e ects that we studied here are small, however, they are still within the
detection limits of the SKA, due to its very high sensitivity. Therefore, the SKA will play
a big role in the study of cosmological radio backgrounds by providing high precision SZE
data.
Description
A thesis submitted to the Faculty of Science,
University of Witwatersrand,
in the ful lment of the requirements for the degree of
Doctor of Philosophy
Johannesburg, South Africa, 2017.
Keywords
Citation
Emritte, Mohammad Shehzad (2017) The study of cosmological radio backgrounds with the Sunyaev-Zel'dovich effect, University of the Witwatersrand, Johannesburg, <http://hdl.handle.net/10539/25114>