A Search for “Dwarf'' Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies

Abstract

We have completed an optical spectroscopic survey of the nuclear regions (r <\n200 pc) of a large sample of nearby galaxies. Although the main objectives of\nthe survey are to search for low-luminosity active galactic nuclei and to\nquantify their luminosity function, the database can be used for a variety of\nother purposes. This paper presents measurements of the spectroscopic\nparameters for the 418 emission-line nuclei, along with a compilation of the\nglobal properties of all 486 galaxies in the survey. Stellar absorption\ngenerally poses a serious obstacle to obtaining accurate measurement of\nemission lines in nearby galactic nuclei. We describe a procedure for removing\nthe starlight from the observed spectra in an efficient and objective manner.\nThe main parameters of the emission lines (intensity ratios, fluxes, profile\nwidths, equivalent widths) are measured and tabulated, as are several stellar\nabsorption-line and continuum indices useful for studying the stellar\npopulation. Using standard nebular diagnostics, we determine the probable\nionization mechanisms of the emission-line objects. The resulting spectral\nclassifications provide extensive information on the demographics of\nemission-line nuclei in the local universe. This new catalog contains over 200\nobjects showing spectroscopic evidence for recent star formation and an equally\nlarge number of active galactic nuclei, including 46 which show broad H-alpha\nemission. These samples will serve as the basis of future studies of nuclear\nactivity in nearby galaxies.\n