The circumnuclear region in the Seyfert 2 galaxy NGC 5953

Abstract

This article presents narrow-band Hα and [O iii] images of the interacting pair of galaxies NGC 5953 (with a Seyfert type 2 nucleus) and NGC 5954 (with a LINER). Long-slit spectroscopy, from [Nev] λ3425 Å to [S iii] λ9532 Å, at intermediate resolution along position angles 44° and 182° through the nucleus of NGC 5953, is also presented. Both objects show a recent burst of star formation in the circumnuclear region, more conspicuous in NGC 5953. The H ii regions are photoionized by a cluster of stars with effective temperature 42 000 K; the ionized gas has a metallicity of three times the solar value, with an overabundance of nitrogen. In the north-eastern part of the nucleus of NGC 5953 there is extended circumnuclear emission produced by a mixture of low- and high-excitation gas, which is kinematically perturbed; this probably reflects photoionization by stars and by an additional source, which may be identified with radiation escaping from the nucleus and/or ionization related to the radio jet, which has a geometry closely related to the line emission. A problem 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-component photoionization models to reproduce the observed line ratios.