Globular Clusters and Spur Clusters in NGC 4921, the Brightest Spiral
  Galaxy in the Coma Cluster
  We resolve a significant fraction of globular clusters (GCs) in NGC 4921, the
brightest spiral galaxy in Coma. Also we find a number of extended bright star
clusters (star complexes) in the spur region of the arms. The latter are much
brighter and bluer than those in the normal star-forming region, being as
massive as 3x10^5 M_odot. The color distribution of the GCs in this galaxy is
found to be bimodal. The turnover magnitudes of the luminosity functions (LF)
of the blue (metal-poor) GCs (0.70<(V-I)<1.05) in the halo are estimated to be
V(max) =27.11+-0.09 mag and I(max)=26.21+-0.11 mag. We obtain similar values
for NGC 4923, a companion S0 galaxy, and two Coma cD galaxies (NGC 4874 and NGC
4889). The mean value for the turnover magnitudes of these four galaxies is
I(max)=26.25+-0.03 mag. Adopting M_I (max) = -8.56+-0.09 mag for the metal-poor
GCs, we determine the mean distance to the four Coma galaxies, 91+-4 Mpc.
Combining this and the Coma radial velocity, we derive a value of the Hubble
constant, H_0 = 77.9+-3.6 km/s/Mpc. We estimate the GC specific frequency of
NGC 4921 to be S_N = 1.29+-0.25, close to the values for early-type galaxies.
This indicates that NGC 4921 is in the transition phase to S0s.
