E. Davoust

Starbursts in barred spiral galaxies - III. Definition of a homogeneous sample of starburst nucleus galaxies

This paper presents optical long-slit spectro- scopic observations of 105 barred Markarian IRAS galax- ies. These observations are used to determine the spectral type (starburst or Seyfert) of emission-line regions in the nucleus and along the bar of the galaxies, in order to de- ne a homogeneous sample of Starburst Nucleus Galaxies (SBNGs). Our selection criteria (ultraviolet excess, far infrared emission and barred morphology) have been very ecient for selecting star-forming galaxies, since our sample of 221 emission-line regions includes 82% nuclear or extranuclear starbursts. The contamination by Seyferts is low (9%). The remaining galaxies (9%) are objects with ambiguous classication (Hii or LINER). The dust content and H luminosity increase towards the nuclei of the galaxies. No signicant variation of the electron density is found between nuclear and bar Hii re- gions. However, the mean H luminosity and electron den- sity in the bar are higher than in typical disk Hii regions. We investigate dierent mechanisms for explaining the excess of nitrogen emission observed in our starburst nu- clei. There is no evidence for the presence of a weak hidden active galactic nucleus in our starburst galaxies. The cause of this excess is probably a selective enrichment of nitro- gen in the nuclei of the galaxies, following a succession of short and intense bursts of star formation. Our sample of SBNGs, located at a mean redshift of 0.015, has moderate H ( 10 41 erg s 1 ) and far in- frared (10 10 L) luminosities. The types are distributed equally among early- and late-type giant spirals with a