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dc.contributor.authorLira, Paulinaen
dc.date.accessioned2018-01-31T11:47:06Z
dc.date.available2018-01-31T11:47:06Z
dc.date.issued1999en
dc.identifier.urihttp://hdl.handle.net/1842/28437
dc.description.abstracten
dc.description.abstractThis thesis reports on the study of a volume-limited sample of 46 galaxies. It forms part of a continuing, multi wavelength program to assess the prevalence of low luminosity nuclear activity in galaxies with a wide range of sizes. X-ray observations are used, together with images at other wavelengths from previous work, to create a list of possible sites of nuclear activity. Optical spectra of these targets are analysed. The X-ray and optical properties of the nuclear regions, and their relationship with the host galaxies, are investigated. Finally, one particular object, NGC4395, is described in detail.en
dc.description.abstractR.OSAT X-ray images were studied for 29 galaxies. Contour maps are presented for all galaxies with detected emission and fluxes are given for all observed point sources. Upper limits are given for galaxies with no detected nuclear sources. In general, X-ray nuclear sources are found to be extremely common. Their fluxes correlate strongly with the host galaxy luminosity (the analysis includes results from the literature for another 4 galaxies).en
dc.description.abstractLong slit, high resolution, ~ 3600 — 6800 A optical spectra were obtained for all the nuclear targets identified during careful examination of radio, IR, optical and X-ray images. Spectra are presented for each target and emission line fluxes are measured. Emission line diagnostic diagrams are used to investigate the nature of the ionising sources of the line-emitting targets. Results are compared with the spectral classification given by ? for galaxies common to both surveys and objects without previous observations are classified. The fraction of optically identified AGN in the sample is obtained.en
dc.description.abstractBased on the observed correlation between X-ray and host galaxy luminosity, the properties of the nuclear X-ray sources are investigated. Nuclear Ha and X-ray luminosities are compared with relationships established for more luminous AGN and with predictions from starburst models. Correlations are also found between nuclear Lla luminosities and host absolute magnitudes for nuclei optically classified as sta.rbursts or AGN. Tentative explanations for the observed correlations are explored.en
dc.description.abstractAs part of the multiwavelength project, optical spectra and X-ray images of NGC 4395, the least luminous known Seyfertl, were obtained. The ROSAT observations show a change in the X-ray flux by a factor of ~ 2 in 15 days. The spectra show a change in both the level and shape of the continuum, becoming bluer when brighter. A power law fit to the observations shows that the spectral shape changes between a low state (with a ~ 2), a medium state (a ~ 1), and a high state (a ~ 0). A week of ground-based optical broad band monitoring of NGC4395 has also given evidence of a variation in the flux by ~ 20% in less than 24 hours.en
dc.publisherThe University of Edinburghen
dc.relation.isreferencedbyen
dc.subjectAnnexe Thesis Digitisation Project 2017 Block 16en
dc.titleNuclear activity in a volume-limited sample of nearby galaxiesen
dc.typeThesis or Dissertationen
dc.type.qualificationlevelen
dc.type.qualificationnamePhD Doctor of Philosophyen


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