Massive star formation in the central regions of spiral galaxies

Context The morphology of massive star formation in the central regions of galaxies is an important tracer of the dynamical processes that govern the evolution of disk, bulge, and nuclear activity. Aims We present optical imaging of the central regions of a sample of 73 spiral galaxies in the Hα line and in optical broad bands, and derive information on the morphology of massive star formation. Methods We obtained images with the William Herschel Telescope, mostly at a spatial resolution of below one second of arc. For most galaxies, no Hα imaging is available in the literature. We outline the observing and data reduction procedures, list basic properties, and present the I-band and continuum-subtracted Hα images. We classify the morphology of the nuclear and circumnuclear Hα emission and explore trends with host galaxy parameters. Results We confirm that late-type galaxies have a patchy circumnuclear appearance in Hα, and that nuclear rings occur primarily in spiral types Sa-Sbc. We identify a number of previously unknown nuclear rings, and confirm that nuclear rings are predominantly hosted by barred galaxies. Conclusions Other than in stimulating nuclear rings, bars do not influence the relative strength of the nuclear Hα peak, nor the circumnuclear Hα morphology. Even though our selection criteria led to an over-abundance of galaxies with close massive companions, we do not find any significant influence of the presence or absence of a close companion on the relative strength of the nuclear Hα peak, nor on the Hα morphology around the nucleus.