Giant radio halos and relics in ACTPol clusters.
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Date
2017
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Abstract
Galaxy clusters are the largest gravitationally-bound structures in the universe. They act as
the largest astrophysical laboratories in the universe and are extremely interesting objects
to study as they are at crossroads between astrophysics and cosmology. In previous decades
the most prominent cluster studies were focused on thermal processes in the intracluster
medium (ICM). However, recent studies have shown that non-thermal studies give a different
perspective on ICM processes.
Giant radio halos and radio relics are examples of this non-thermal diffuse radio emission.
Giant radio halos are believed to originate from synchrotron radiation resulting from the
re-acceleration of relativistic electrons in the cluster's magnetic field by the turbulent energy
following merger activity. Radio relics, another form of non-thermal diffuse radio emission,
have been identi ed as possible tracers of merger shock waves. The study of diffuse radio
emission has a number of open questions such as; the observed bimodality in the radio power
versus X-ray luminosity plot. The bimodality could partly be due to the identi cation of
halos and relics in clusters without a well-de ned selection function.
In this thesis, we studied giant radio halos and relics in a homogeneous, mass-selected
sample of sixteen clusters selected via the Sunyaev- Zel'dovich (SZ) effect by the Atacama
Cosmology Telescope (ACT) with polarization sensitive receivers (ACTPol). We carried out
a radio wavelength study using data obtained from the Giant Metrewave Radio Telescope
(GMRT) for four of these clusters. This subsample of four clusters will be added to the
larger sample, eight of which have archival data, and four of which will be proposed for
observations in the next GMRT observation cycle. We used the GMRT data at 610 MHz to
search for diffuse radio emission in each cluster. We applied various uv-cuts and tapers to
isolate the low-resolution emission in the target fi eld. For two of the four observed clusters,
we tentatively discovered extended radio emission at a signifi cance level of at least 3o' We
then measured radio
fluxes for compact sources in the cluster region. We were able to
calculate spectral indices for the compact sources that were cross-matched in FIRST.
Description
Master of Science in Mathematics, Statistics and Computer Science. University of KwaZulu-Natal, Durban, 2017.
Keywords
Theses - Applied Mathematics.