Optical Spectroscopy of the Central Regions of Bright Barred Spiral Galaxies

Abstract

Optical red spectra of a set of 18 bright barred spiral galaxies are presented. The study is aimed at determining the local kinematics, and the physical conditions of ionized gas in the compact nucleus (inside a diameter of 5") and in the circumnuclear regions (inside a diameter of 20"). Only 8 galaxies showed bright emission from their east and west side of the nucleus. The spectrum of each region was analized separately. In other 10 galaxies the line emission was so weak that we were only able to obtain an average spectrum of the central emission. No emission was detected in the remaining 8 galaxies. An estimate of the dynamical mass is presented based on the observed velocities in the circumnuclear regions. In NGC 4314 and NGC 6951, that show H_alpha emission distributed in circumnuclear ring structures, we determine the [NII]/H_alpha and [SII]/H_alpha ratios for the eastern and western regions of the rings. The velocity difference for the two sides is used to derive the rotation velocity of the gas around the compact nucleus. The ratio [NII]6583/H_alpha is a factor of 2 larger in the compact nucleus of NGC 6951 than in its western side. The electron gas densities have been estimated from the [SII] lines ratio.