FAR-INFRARED LUMINOSITY FUNCTIONS OF NORMAL GALAXIES

A volume-limited sample (less-than-or-equal-to 1400 km s-1; corrected for local motion) is constructed from the Zwicky catalog and IRAS data base to examine the far-infrared (FIR) luminosity functions of normal galaxies, and to investigate possible relationships between FIR emission and galaxy morphology. Quantitative and unbiased treatment is provided by "survival analysis" statistical methods. We find that the FIR distributions of normal galaxies are better fit by lognormal than Schechter functions. The total FIR emissivity (8 to 115-mu-m) of normal galaxies is approximately equal to half their emission in the B plus V optical bands. Normal galaxy FIR emission is uncorrelated with the basic S0-Sm Hubble sequence of spiral galaxy morphology, but appears to be affected by de Vaucouleurs' revised morphological classifications based on inner rings and S-shaped arms. Spirals with bars and inner rings are systematically fainter than unbarred spirals. We suggest that bars and rings reduce the amount or spatially confine the dust in spiral disks, resulting in lower efficiency conversion of optical and UV photons into the infrared.