A search for dead QSOs among nearby luminous galaxies.

Abstract

Quasi-stellar objects (QSOs) and active galactic nuclei (AGNs) with luminosities $\geq$10$\sp{12}$ L$\sb\odot$ (where L$\sb\odot$ is the solar luminosity) are generally presumed to be powered by accretion of matter onto a black hole with mass of $\geq$10$\sp9$ M$\sb\odot$ (where M$\sb\odot$ is the solar mass). When the host galaxy is exhausted of matter capable of feeding the central black hole, the energy output rapidly decreases leaving behind a dead QSO engine. Confirmation of this model would then be provided by the identification of dead engines in nearby galaxies. The observed stellar kinematics in the nuclei of the galaxies, when combined with dynamical models, indicate whether unseen central masses are present. This dissertation describes the first results of an extensive project to analyze high spatial resolution observations of the nuclei of nearby galaxies with similar morphological properties as QSO host galaxies. Long slit optical spectra of spiral galaxies NGC 2613, NGC 4699, NGC 5746, and NGC 7331 are analyzed with a cross correlation method to measure the stellar kinematics. Using the observations in conjunction with a maximum entropy method to model the dynamics shows that unseen masses in the nuclei of these four galaxies are not required in order to explain the observations. The upper limit of possible black hole masses are 7 $\times$ 10$\sp8$ M$\sb\odot$ for NGC 7331 and few $\times$ 10$\sp9$ M$\sb\odot$ for the other three galaxies. In addition, long slit optical spectroscopy of many of the candidate galaxies show weak nuclear emission lines. The ratios of the emission lines indicate that most of the galaxies harbor low-luminosity AGNs or LINERs (Low-Ionization Nuclear Emission Line Regions). Determining the local space density of $\sim$10$\sp9$ M$\sb\odot$ black holes provides a constraint on evolution scenarios of the QSO population because this space density should be a measure of the rate of the evolution from large redshifts to the present epoch.