THE CIRCUMNUCLEAR REGION IN THE SEYFERT-2 GALAXY NGC-5953

This article presents narrow-band H alpha and [O III] images of the in teracting pair of galaxies NGC 5953 (with a Seyfert type 2 nucleus) an d NGC 5954 (with a LINER). Long-slit spectroscopy? from [Nev] lambda 3 425 Angstrom to [S III] lambda 9532 Angstrom, at intermediate resoluti on along position angles 44 degrees and 182 degrees through the nucleu s of NGC 5953, is also presented. Both objects show a recent burst of star formation in the circumnuclear region, more conspicuous in NGC 59 53. The HII regions are photoionized by a cluster of stars with effect ive temperature 42 000 K; the ionized gas has a metallicity of three t imes the solar value, with an overabundance of nitrogen. In the north- eastern part of the nucleus of NGC 5953 there is extended circumnuclea r emission produced by a mixture of low- and high-excitation gas, whic h is kinematically perturbed; this probably reflects photoionization b y stars and by an additional source, which may be identified with radi ation escaping from the nucleus and/or ionization related to the radio jet, which has a geometry closely related to the line emission. A pro blem is identified with the line ratios involving the infrared [S III] lines, which may reflect a problem with the sulphur atomic parameters , depletion of the sulphur abundance or the inadequacy of one-componen t photoionization models to reproduce the observed line ratios.