The Tully-Fisher Relation in Coma and Virgo Cluster S0 Galaxies

We use the Tully-Fisher relation (TFR) to compare the behavior of S0 and late-type spiral galaxies. We determine circular velocities based on stellar kinematics derived from stellar absorption line spectroscopy for 10 S0's in the Coma Cluster and eight S0's in the Virgo Cluster. We combine these results with similar measurements of 13 Coma S0 galaxies obtained previously. We find that there is only a small offset, Δm_H ∼ 0.2, in the H-band luminosity at a given circular velocity, v_c ∼ 200 km s^-1, between S0 and late-type spirals. This result implies a similar total H-band mass-to-light ratio (within an effective radius) among disk galaxies of different Hubble types. As the older stellar population in S0's is dimmer, this suggests a somewhat larger fraction of stellar mass in these S0's than in late-type spirals. We also find that the relation between (I- and H-band) luminosity and v_c for the S0 galaxies is at best poorly defined and has a scatter of ∼1 mag, significantly larger than the TFR for late-type spirals, where the observed I- and H-band scatter is σ ∼ 0.3–0.5 mag. This substantial scatter confirms the original findings of Dressler & Sandage and is similar to that found in a study by Neistein and coworkers of 18 nearby S0 galaxies in the field where σ_I ∼ 0.7 mag, but differs from the small scatter found by Mathieu and coworkers, σ_I ∼ 0.3 mag, for six nearby S0's. Our results suggest that differing formation histories can lead to S0's with diverse properties and that S0's are more likely to be the outcomes of minor mergers or some "preprocessing" in groups of galaxies falling into clusters, rather than simply late-type spirals that have been stripped of their gas but are kinematically preserved. We suggest that it is likely that many mechanisms, such as slow encounters, tidal interactions, and gas stripping, may have occurred in the lifetimes of the galaxies and produced the heterogeneous class of S0's that are observed today.