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

Abstract

ABSTRACTAccurate estimates of spectral parameters are essential to investigate the physical conditions in active galactic nuclei (AGNs). In particular, 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 line width or from the relation between the AGN luminosity and the width of the broad Hβ component. Two different luminosity values are important: one is derived from the monochromatic flux at 5100 Å, and the other is the integrated luminosity for the broad component of Hβ. The spectral parameters are also a fundamental key to obtaining a reliable classification. Spectroscopic observations with a resolution of 4.5 Å were performed for a sample of eight galactic nuclei extracted from the Second Byurakan Survey, in addition to one galaxy companion of SBS 1204+505B. The equivalent width 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–quasi‐stellar objects (QSOs) (i.e., seven objects). In particular, these include the amount of reddening, B - V color excess, extinction coefficient, and optical depth in the V band, at the Hα and Hβ wavelengths, and at 5100 Å. The size of the broad‐line region was also estimated for seven objects, as were the central black hole masses. Three mass estimates were usually performed for each object and were 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 galaxy companion of SBS 1204+505B is reported as being a nuclear starburst galaxy.