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Title: A census of hidden nuclei in radio galaxies
Author: McAllister, Joanna
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2000
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There is now convincing evidence from imaging and polarization studies that the appearance of Active Galactic Nuclei (AGN) depends strongly on orientation. This thesis proposes to address this question by imaging a sample of low-redshift radio-selected galaxies in the infrared, where the obscuration due to dust is reduced, in the hope of providing an unbiased survey of the line-of-sight extinctions towards AGN and the relative numbers of hidden sources. The low redshift of the sample allows the study of similar luminosity Fanaroff-Riley class I and class II sources, with the opportunity to explore the nuclear luminosity function of lower luminosity objects than in previous studies. Infrared K and L' images were obtained for 28 galaxies. The non-thermal nuclear contribution to the K band flux is then estimated by subtracting a fitted two-dimensional surface brightness galaxy model from each image. The stellar contribution to the L' flux is estimated by fitting simple stellar population models to the optical spectra of a subsample of the objects and calculating the infrared K-L' colour of these fitted populations. Optical spectra were obtained for 13 objects in the sample. The reddening towards the nucleus is calculated by subtracting the intrinsic K-L' colour of a quasar or starburst from the observed value. Nuclear sources are detected in 10 members of the sample. The intrinsic luminosities of all these sources would put them above the quasar/Seyfert dividing line of Mv < -23, making them possible candidates for obscured radio-loud quasars. The correlation between extinction and orientation is then explored. The expected anti-correlation between core-to-lobe ratio R and extinction is not apparent, whilst a possible correlation between extinction and galaxy size is observed, larger galaxies appearing to contain more dust.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available