This thesis presents a detailed multi-wavelength study of radio sources. A major part of the thesis
focuses on radio sources in the FIRST survey while the latter part of the thesis studies low
redshift radio galaxies in X-ray selected galaxy clusters. In the first part of the thesis a cross
correlation analysis of FIRST radio sources with optical data from the NDWFS and infrared
data from the FLAMINGOS survey in the Boötes and Cetus fields was performed. Optical
counterparts were found for 76% (688/900) of sources in one band or more i.e., Bw, R, I or K.
Photometric redshifts for these sources have been computed using the Hyperz code. The red-shifts
obtained are fairly consistent with those expected from the K−z relation for brighter radio
sources. A total number of 57 counterparts have extremely red colour (R− K > 5). Photometric
redshifts derived using Hyperz imply that these Extremely Red Object (ERO) counterparts to
FIRST radio sources are mostly located in the range z ∼ 0.7 −2, with the bulk of the population
at z ∼ 1. A total of 25 ERO counterparts to FIRST radio sources were identified in R, J and
K bands. These objects were separated into passively-evolving and dusty star-forming galaxies
using their R, J and K colours. The relatively blue J − K colour of these galaxies suggest that
most (72%, 18/25) are elliptical galaxies rather than dusty starburst galaxies.
Using data from the Chandra XBoötes survey, a total of 92 (10%) FIRST radio sources were
identified above the X-ray flux limit, fX (0.5 − 7) keV = 8 × 10−15 erg s−1 cm−2, and of these 79 optical counterparts are in common to the radio-X-ray matches. The majority (68%) of the
radio-X-ray matched population were found to have −1 < log fX/ fopt < +1 indicative of AGNs.
There is a significant population (23%) with high X-ray-to-optical flux ratio (log fX/ fopt > 1),
suggesting high redshift and/or dust obscured AGN. In addition, there is also a population of
sources that are X-ray faint optically bright sources with log fX/ fopt < −1. Spectroscopic identifications
were found for 22 of the 79 sources. These optical spectra were dominated by broad
line AGNs and also included narrow emission line galaxies. It was found that many classes of
objects contribute to the X-ray/radio emission including quasars, BL Lacs, starburst galaxies,
normal galaxies and galaxies with both AGN and starburst activity.
This thesis also investigated the clustering analysis of FIRST radio sources optically identified
in the SDSS DR6 survey using the two point angular correlation function ω(θ). The
matched sources were found to have a larger amplitude of clustering compared to the full catalogue
of radio sources consistent with similar studies in the literature. The angular correlation
function was measured for different magnitude limited and flux limited subsamples. It was
found that the angular correlation function scales with the depth of the optical survey as expected,
whereas the amplitude of the angular correlation function increases as the radio flux
increases.
The last part of this thesis is devoted to studying radio galaxies in galaxy clusters at high
frequencies to explore their contamination to the Sunyaev-Zel’dovich effect signal in these clusters.
A total of 139 galaxies at low redshift (z < 0.25) in X-ray selected clusters were observed
at four frequencies, 4.9, 9, 22, and 43 GHz using the NRAO Very Large Array. It was found that
more than half of the observed sources have steep microwave spectra with steep spectral index,
α < −0.5, as generally expected. However, about 60% of the unresolved or barely resolved
sources have flat or inverted spectra. Most of these sources show an upward turn in flux at
ν > 22 GHz, implying a higher flux than would be expected from an extrapolation of the lower
frequency flux measurements. Our results quantify the need for careful source subtraction in
increasingly sensitive measurements of the Sunyaev-Zel’dovich effect in clusters of galaxies. / Thesis (PhD)-University of KwaZulu-Natal, Westville, 2009.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/445 |
| Date | January 2009 |
| Creators | El Bouchefry, Khadija. |
| Contributors | Rash, Jonathan Paul Stuart., Moodley, Kavilan. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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