THE EFFECT OF INCLINATION-DEPENDENT SELECTION ON IRAS GALAXY DETECTION RATES

We have investigated the suggestion by Burstein and Lebofsky that Sc spiral galaxies are optically thick at 100-mu-m, when viewed edge-on. Having examined the inclination dependence of the 100-mu-m surface brightness and 100 to 60-mu-m color for a sample of UGC Sc spirals, we find no evidence to support large optical depth at 100-mu-m. By comparing the inclination distribution of these Sc spirals with a random distribution, we find an excess of edge-on [log (a/b) > 0.7] spirals. We interpret this as a systematic misclassification of edge-on spirals as Sc and an increase in diameter with inclination in the UGC. We therefore conclude that there is no evidence to support the notion that edge-on Sc galaxies are optically thick at 100-mu-m.