A key result of the Two Micron All Sky Survey (2MASS) was the discovery of a popula tion of AGN that appear redder than their traditional UV/optical selected counterparts at IR wavelengths. In order to investigate the nature of 2MASSselected AGN, in this thesis I present optical spectra and near to midIR photometry for a representative sam ple of 29 nearby (z<0.28) 2MASSselected AGN with red nearIR colours (JK S # > 2.0), comparing my findings with those obtained for comparison samples of UV/optical se lected AGN. The spectra show a remarkable variety, including moderately reddened type 1 objects (58%), type 1 objects that appear similar to traditional UV/optically selected AGN, narrowline Seyfert 1 AGN (14%), type 2 AGN (21%) and HII/composite objects (7%). Although the median Balmer decrement suggests significant optical reddening compared to the comparison samples, some objects show relatively little (if any) reddening in their optical spectra. In addition, the near to midIR photometric results reveal that a fraction of the broadline objects in the 2MASS sample (26%) have unusually blue 2.173.4µm colours when compared to the rest of the sample, suggesting that their red nearIR colours are due, at least in part, to emission by a component of hot dust with an unusually high covering factor. Overall, a variety of mechanisms is required to explain the red nearIR colours of the 2MASS objects: although some are moderately reddened type 1 objects, or `genuine' type 2 objects that are highly obscured by the central torus structure, others show unusually strong emission from dust close to the AGN. This is confirmed by simple modelling of the colours of the 2MASS and comparison samples However, I find no clear evidence that the 2MASS objects are young, dust enshrouded AGN. In addition to the analysis of the full 2MASS sample, I present a detailed study of one of the red 2MASS AGN (J1131+16) which shows unusually strong forbidden high ionization lines. This study demonstrates the potential of optical spectroscopic studies of the FHILs for understanding the nature of the obscuring dust structure of AGN.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:589142 |
| Date | January 2012 |
| Creators | Rose, Marvin |
| Contributors | Tadhunter, Clive |
| Publisher | University of Sheffield |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://etheses.whiterose.ac.uk/4490/ |
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