A SEARCH FOR DWARF SEYFERT NUCLEI .3. SPECTROSCOPIC PARAMETERS AND PROPERTIES OF THE HOST GALAXIES

We have completed an optical spectroscopic survey of the nuclear regio ns (r less than or similar to 200 pc) of a large sample of nearby gala xies. Although the main objectives of the survey are to search for low -luminosity active galactic nuclei and to quantify their luminosity fu nction, the database can be used for a variety of other purposes. This paper presents measurements of the spectroscopic parameters for the 4 18 emission-line nuclei, along with a compilation of the global proper ties of all 486 galaxies in the survey. Stellar absorption generally p oses a serious obstacle to obtaining accurate measurement of emission lines in nearby galactic nuclei. We describe a procedure for removing the starlight from the observed spectra in an efficient and objective manner. The main parameters of the emission lines (intensity ratios, f luxes, profile widths, and equivalent widths) are measured and tabulat ed, as are several stellar absorption-line and continuum indices usefu l for studying the stellar population. Using standard nebular diagnost ics, we determine the probable ionization mechanisms of the emission-l ine objects. The resulting spectral classifications provide extensive information on the demographics of emission-line nuclei in the nearby regions of the universe. This new catalog contains over 200 objects sh owing spectroscopic evidence for recent star formation and an equally large number of active galactic nuclei, including 46 that show broad H alpha emission. These samples will serve as the basis of future studi es of nuclear activity in nearby galaxies.