New Insights from HST Studies of Globular Cluster Systems II: Analysis of 29 S0 Systems

Abstract

We examine the globular cluster systems (GCS) of a sample of 34 S0 galaxies from a WFPC2 snapshot survey in the V and I-bands. Of these 34 galaxies, 29 have measurable globular cluster systems. The mean color of the GCSs of individual galaxies vary from V-I=0.85 mag to V-I=1.17 mag. The average color of GCSs in all 29 S0 galaxies, V-I=1.00 +/- 0.07 mag, is similar to the value of V-I=1.04 +/- 0.04 derived for ellipticals in a companion paper. The mean metallicity of a cluster system is correlated to the luminosity (or mass) of the host galaxy, but is not dependent on the Hubble type. Our measurements of the local specific frequency, on the other hand, confirm that the cluster formation efficiency is a function of Hubble type. The mean local specific frequency of our sample within the WFPC2 field-of-view is 1.0 +/- 0.6, lower than S_(N Local)=2.4 +/- 1.8 derived for ellipticals in a similar analysis. Although we are able to confirm a bimodal color distribution in only one galaxy from the shallow 'snapshot' images analyzed in this paper statistical tests suggest that 10-20% of S0s are bimodal it at the present level of photometric accuracy. There are no significant trends in GCS properties with membership or location of the S0 host in a galaxy cluster. We have measured the turnover luminosity of the globular cluster luminosity function (GCLF) for the richest few GCSs and find the GCLF distances to be in agreement with other estimates. The globular clusters in S0 galaxies have average half-light radii of ~2.6 pc which is similar to that of other galaxies, including our own.