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Measuring the radio spectra of compact radio sources

Tjoa, J.N.K.Y. (2016) Measuring the radio spectra of compact radio sources. Bachelor's Thesis, Astronomy.

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A study is performed into the angular extensions and differential number densities of gigahertzpeaked spectrum (GPS) compact radio sources (CRS) at low flux densities. An introduction is given into the topics of active galactic nuclei (AGN), CRSs and GPS, followed by a discussion of physical mechanisms abound in these sources. The selected sample of 45 CRSs is discussed and spectrally fitted using least squares and Markov-chain Monte Carlo algorithms, finding about half of the sources to indeed be GPS. Use is made of the K-z relation for radio sources, relating K-band magnitude to redshift, which is used to obtain redshifts for 14 sources without spectroscopic data, leading to a redshift completeness level in the sample of 66%. Number counts of redshift, peak flux density and peak frequency are made, showing no signs of bimodal behaviour. Obtained results are synthesised with data from Snellen et al. concerning angular size, which is shown to indeed decrease as expected at low flux densities and high frequencies. An unexpected offset is discovered in the small angular size-regime, which might hint at unusual behaviour of extremely young CRSs. Differential number counts of the number density per peak flux are performed, leading to the conclusion that a new population of unexplored, faint GPS sources may exist at low radio frequencies. Concluding remarks are provided as to how to proceed on this exploratory path, suggesting additional observations at differing frequencies, a redo of the Snellen et al. sample and exploration of the extremely high and low frequency ends of the known CRS range.

Item Type: Thesis (Bachelor's Thesis)
Degree programme: Astronomy
Thesis type: Bachelor's Thesis
Language: English
Date Deposited: 15 Feb 2018 08:25
Last Modified: 15 Feb 2018 08:25

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