A comparison of Coma Cluster S0 galaxies with the Tully-Fisher relation for late-type spirals

We present I-band photometry for 13 S0 galaxies in the Coma Cluster and estimate their circular velocities based on stellar kinematics derived from stellar absorption-line spectroscopy. We find that there is at most a small offset, Δm_I ≤ 0.2, in the I-band luminosity at a given circular velocity, v_c ∼ 200 km s^-1, between late-type spirals and the S0 galaxies studied here. This result implies a similar total I-band mass-to-light ratio (within an effective radius) among disk galaxies of rather 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-band luminosity and v_c for the S0 galaxies is at best poorly defined and has a scatter of σ_I ∼ 0.5 mag, significantly larger than the Tully-Fisher relation (TFR) for late-type spirals in clusters, where the observed I-band scatter is σ_I ≲ 0.3 mag. This substantial scatter is only somewhat less than that found by Neistein et al. in a recent study of 18 nearby S0 galaxies in the field (σ_I ∼ 0.7 mag), implying that no tight TFR holds for field S0 galaxies. These results suggest that differing formation histories can lead to S0's with diverse properties. Our analysis of S0's in the Coma Cluster differs from previous analyses in two important respects: the data are independent of distance estimate errors, and they contain S0's formed in a more homogeneous environment.