HI CONTENT AND FIR EMISSION OF SO GALAXIES

We have examined the relationship between H I content and FIR emission of a sample of 252 S0 galaxies. Using statistical methods that take limit values into account (survival analysis), we evaluate a best-fit linear regression line for the logarithm of the H I content versus the FIR emission (both scaled by the blue flux) with a slope of roughly unity. This slope is not significantly different for subsets of barred versus unbarred galaxies; however, the slopes differ for S0 and SB0 galaxies (the "S0 sample") versus S0/a and SB0/a galaxies (the "S0/a sample") at the 96% confidence level. Applying the Kaplan-Meier estimator and a battery of two-sample tests, we find that the presence or absence of bars does not affect either the relative H I content or FIR emission in our sample. These tests do show the S0/a sample to have relatively more H I and stronger FIR emission than the S0 sample. The presence or absence of bars, and the differences between S0 and S0/a systems do not significantly affect the distribution of the 60-100-mu-m flux ratio (r60/100). Roughly 34% of our sample has r60/100 greater-than-or-equal-to 0.447, the critical value of Helou above which a majority of the FIR emission is expected to be due to star formation. Repeating these analyses on a sample from which all systems with known nuclear emission have been removed does not yield significantly different results. However, among the subset of known AGN, the relative FIR emission and relative H I content are greater than for the normal S0 galaxies to many sigma. Our results indicate that, by and large, S0 galaxies have a normal ISM, at least for those components probed by the H I line and satellite FIR. Where there are glaring exceptions to this, comparison with other observations indicates that those systems with relatively more H I than expected on the basis of their FIR emission appear to have accreted their H I gas. Those systems with excess FIR emission for their H I content may be examples of galaxies that have been swept of their H I gas, or that are currently undergoing bursts of enhanced star formation.