CIRCUMNUCLEAR STAR-FORMATION IN ACTIVE GALAXIES

We study the gas kinematics and chemical abundances in the inner regio ns of six galaxies with active galactic nuclei. The galaxies were sele cted for having star-forming regions in rings or spirals within a few kiloparsecs of the nucleus. The goal of the project is to search for a ny connections between the gasdynamics, the chemical abundances, and t he nuclear activity. Narrowband images have been obtained to map out t he ionized gas. Medium-dispersion long-slit spectroscopy at several po sitions over the nuclear region has been used to obtain the gaseous ve locity field and distribution of excitation. The H II regions in the r ings are located near the turnover point of the rotation curves, sugge sting association with the inner Lindblad resonance. The nuclear ring in the LINER NGC 1326 may be located between the two inner Lindblad re sonances, and the inner rings in the Seyfert 2 galaxy NGC 3081 and the LINER/Seyfert 1 NGC 7213 may be associated with the Omega - kappa/4 r esonance. A warm ionized medium (WIM) is found to pervade the inner re gion in all galaxies. There is a correlation between the [N II]/H alph a and [S II]/Her ratios and the FWHM of the [N N] lambda 6584 emission line in this WIM, indicating that shocks contribute to the ionization of the gas. We show that contamination by this diffuse emission incre ases the measured [N II]/H alpha and [S II]/H alpha ratios at H II reg ions close to the nuclei and thus may account, in part, for the system atically higher [N II]/H alpha and [S II]H alpha found in the present work and by previous authors for near-nuclear H n regions compared wit h H n regions farther out in the disk of the galaxy. In the present pa per, we correct for this contamination by interpolating the contributi on of the WIM at the H n regions and subtracting it off. Oxygen and ni trogen abundances are obtained for 18 H II regions and are extrapolate d to obtain the abundance of the nuclear gas, which is found to range from solar to 2 times solar for oxygen and from 2 to 4 times solar for nitrogen. Such values are similar to those observed in nonactive gala xies with the same luminosity and morphological type and do not suppor t the idea that the central regions of active galaxies have undergone unusual chemical processing.