The effects of interactions on spiral galaxies. I - Nuclear activity and star formation

Abstract

The authors have obtained spectra of the nuclei of 161 interacting spirals, and compared their properties to those of a complete sample of field spirals. They find that the interacting systems show: (1) Significantly higher levels of emission, in equivalent width and luminosity. (2) More active and extensive nuclear star formation, over all Hubble types. (3) More frequent Seyfert nuclei among close pairs, but fewer among very disturbed (post-encounter) systems. (4) Fewer low-ionization nuclei, which have presumably been turned into Seyferts or masked by nuclear H II regions. The higher incidence of Seyferts in the complete sample supports the notion of central compact objects' being common but normally quiescent in luminous spirals, while their deficiency among distorted pairs suggests that these objects may become gas starved.