The IRAS Bright Galaxy Sample. IV - Complete IRAS observations

Abstract

Total flux densities, peak flux densities, and spatial extents, are reported at 12, 25, 60, and 100 micron for all sources in the IRAS Bright Galaxy Sample. This sample represents the brightest examples of galaxies selected by a strictly infrared flux-density criterion, and as such presents the most complete description of the infrared properties of infrared bright galaxies observed in the IRAS survey. Data for 330 galaxies are reported here, with 313 galaxies having 60 micron flux densities > 5.24 Jy, the completeness limit of this revised Bright Galaxy sample. At 12 micron, 300 of the 313 galaxies are detected, while at 25 micron, 312 of the 313 are detected. At 100 micron, all 313 galaxies are detected. The relationships between number counts and flux density show that the Bright Galaxy sample contains significant subsamples of galaxies that are complete to 0.8, 0.8, and 16 Jy at 12, 25, and 100 micron, respectively. These cutoffs are determined by the 60 micron selection criterion and the distribution of infrared colors of infrared bright galaxies. The galaxies in the Bright Galaxy sample show significant ranges in all parameters measured by IRAS. All correlations that are found show significant dispersion, so that no single measured parameter uniquely defines a galaxy's infrared properties. Galaxies selected to be "warm" and "cold" in the observed ratio of flux densities at 25 and 60 micron can be distinguished in several of the infrared properties. For the galaxies in the Bright Galaxy sample both the ratio of flux densities Snu_,(60 micron)/Snu_,(100 micron) and Snu_, (12 micron)/Snu_,(25 micron) correlate with infrared luminosity, and more significantly with the ratio of infrared-to-visible flux. The relation between these two ratios of flux densities, found previously by several workers, holds for the sample, with different slopes appearing to exist for the warmer and colder galaxies in the sample. It is suggested that single photon heating of small grains, often the dominant source of 12 and 25 micron radiation from galaxies, significantly affects the emission of some galaxies at 60 micron, while optical depth effects appear to alter the emergent radiation at 12 and 25 micron. The warmer galaxies generally have less dust mass at a given infrared luminosity than do the cold galaxies.