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In this Master's project, the X-ray nuclear properties of a sample of brightnearby galaxies are explored. This is done by matching their comprehensiveoptical spectroscopic classification to the latest available XMM-Newtoncatalogue - 3XMM-DR4. The good coverage (approx. 38 per cent) ensures that astatistically representative sample is investigated. All nuclear andmorphological subsets found within the original sample of 486 galaxies areencompassed, but early-type galaxies and galaxies with optical featurescharacteristic for active galactic nuclei (AGN) are favoured. The results fromthe investigation of the properties of our cross-matched sample are overallconsistent with the presence of a large fraction of X-ray - detectedlow-luminosity AGN (LLAGN). The X-ray - detected galaxies within our HII andtransition-LINER subsets are of particular interest, as they could harbourLLAGN missed by optical spectroscopic selection. The properties of these nucleiare explored by X-ray spectral fitting of available XMM-Newton observations.The majority of the examined spectra are found to be consistent with a thermalplasma model and an underlying power-law continuum, and the relativecontributions of a potential LLAGN and of thermal emission to the sourceluminosity are presented. In the case that these spectra are not highlycontaminated, as confirmed for some of the nuclei by examining availablehigher-resolution Chandra images, we classify approx. 43 per cent of the HIInuclei and 40 per cent of the transition-LINER nuclei as optically undetectedLLAGN-candidates. This classification is found to be reasonably successful,given the project limitations, when compared to X-ray and multi-wavelengthresults found in literature for many of the nuclei.

Sleeping Giants? - X-ray search for low-luminosity AGN candidates in nearby optically bright galaxies