Infrared emission in paired galaxies. II - Luminosity functions and far-infrared properties

We have studied the optical and FIR luminosity functions, as well as other FIR statistics, for a sample of galaxy pairs selected from the Catalogue of Isolated Pairs of Galaxies in the Northern Sky (CPG). A comparison has been made with two control samples selected from the Catalogue of Isolated Galaxies (CIG). We find the following: 1. Approximately 10% of field galaxies are in isolated pairs. 2. The optical luminosity functions for late-type (SS), early-type (EE), and mixed (ES) pairs show enhancement at the bright end relative to control samples. 3. The optical luminosity function reveals a complete absence of dwarf EE pairs in the CPG (fainter than Mₚg_ = -19). 4. SS pairs dominate the bright end of the IRAS luminosity function (Lfir_ > 2 x 10¹1^ Lₛun_), while their contribution to the faint end (Lfir_ = 10¹0^ Lₛun _), which indicates an enhancement in the FIR emission. 8. SS pairs also show statistically significant enhancements in their mean FIR to optical luminosity ratio (~ 3 σ) and FIR color ratio (~ 5 σ), compared to isolated spiral/irregular galaxies. 9. SS pairs with signs of interaction and with component separation less than the diameter of the primary show significantly higher mean FIR-to-optical luminosity ratio and mean FIR color ratio compared not only with isolated spiral/irregular galaxies, but also with other SS pairs. These "close-interacting" (CLO) pairs represent ~ 40% of all SS pairs in the CPG. 10. Only one component (the FIR bright component) in wide SS pairs (SS pairs other than CLO) is (marginally) FIR enhanced. A considerable number of CLO SS pairs show evidence for enhancement in both components.