Studies of IRAS sources at high galactic latitudes. IV - New redshifts and the spectroscopic properties of IRAS galaxies

The authors report data (redshifts, line and continuum fluxes) for all galaxies observed in order to complete the redshift survey described in Paper II (see 41.157.038). The galaxies involved contain an interesting sample in themselves, including the most "IR-active" objects. Most of them show emission lines, stronger than those found in optically selected spiral galaxies, and characteristic of normal H II regions, suggesting a burst of star formation as the basic energy source. There is considerable reddening towards the emission-line regions, and towards the unobserved UV sources, most of the energy emerging in the IR. A minority of the cases show high-excitation emission lines, and these are also distinguished by their IR colours, typical luminosities and emission-line strengths. Type 2 Seyferts outnumber Type 1s by 2 to 1. It remains possible that some of the low-excitation objects are highly reddened high-excitation objects.