Physical Parameters and Classification of Eight Galactic Nuclei from the Second Byurakan Survey

Abstract

Accurate spectral parameters estimates are essential to investigate the physical conditions in AGNs. Particularly, intrinsic reddening can be estimated from the Hα/Hβ ratio of the narrow line components. The mass of the central black hole can be obtained from the stellar velocity dispersion in the bulge, which can be estimated from the [O III] λ5007 width, or by the relation between the AGN luminosity and the width of the broad Hβ component. Two different luminosity values are important: one derived from the monochromatic 5100Å, and the integrated luminosity for the broad component of Hβ. The spectral parameters are also a fundamental key to obtain a reliable classification. Spectroscopic observations with a resolution of 4.5Å were performed for a sample of eight galactic nuclei extracted from the Second Byurakan Survey, and one companion galaxy of SBS 1204+505B. The EW and FWHM of the emission lines were measured, and useful line ratios and diagnostic diagrams were used for object classification and reddening estimates. Intrinsic reddening quantities were calculated for all non QSO, i.e. seven objects. Particularly the amount of reddening, B −V color excess, extinction coefficient and optical depths in the V band, at Hα and Hβ wavelengths, and at 5100Å. The broad line region size was also estimated for seven objects, as well as the central black hole masses. Three mass estimates were usually performed for each object and compared. A peculiar line, probably He I λ5048, is detected in the QSO SBS 1626+554. Evidence for a stratified narrow line region is found for the two narrow line Seyfert 1 galaxies included in the sample. A revised classification is proposed for two objects, and the companion galaxy of SBS 1204+505B is reported as a nuclear starburst galaxy.