THE INFLUENCE OF ENVIRONMENT ON GAS AND DUST IN S0 GALAXIES

The H I content and far-infrared continuum properties of a complete sample of S0 galaxies in the Local Supercluster (z<0.01) are investigated in an attempt to understand the origin of their low gas and dust content. The major thrust of this analysis is the comparison of the global H I and far-infrared properties of objects in regions of both high- and low-density and potential for tidal interaction. The restriction of the sample to the northern celestial hemisphere portion of the Local Supercluster allows the computation of density and tidal damage parameters for the comparative analysis from a relatively complete redshift catalog. Within the Local Supercluster, the S0 galaxies are found in regions of local galaxy density differing by more than a factor of 100. S0's in high-density environments are H I deficient compared to those in lower-density regions, a result like that found previously for later-type spiral galaxies. The S0's in the highest-density regions (the core of the Virgo Cluster) are characterized by an H I surface density about a factor of 4 lower than those in lower-density regions. The depletion of H I in galaxies is more severe among early-type spirals than among Sc galaxies, but the variation in the degree of depletion is not monotonic along the spiral sequence. In fact, the presence of H I in gas-rich S0's can often be explained as the result of the recent accretion of a gas-rich companion. The far-infrared continuum emission is found to depend only marginally on environment among the early-type spirals and S0's. However, the FIR emission in Sc's is similar in high- and low-density regions, indicating that the dust emission is not strongly associated with the H I gas. This apparent contradiction could result from the dust being associated primarily with molecular gas or could be due to the removal of H I in the outer parts of the galaxy where the radiation field is low or the gas-to-dust ratio is large. Galaxies noted to contain significant amounts of dust upon optical inspection often show large ratios of far-infrared to H I flux.