The Formation of Spheroids in Early-Type Spirals: Clues From Their
  Globular Clusters
  We use deep Hubble Space Telescope images taken with the Advanced Camera for
Surveys (ACS) in the F475W and F814W filters to investigate the globular
cluster systems in four edge-on Sa spiral galaxies covering a factor of 4 in
luminosity. The specific frequencies of the blue globular clusters in the
galaxies in our sample fall in the range 0.34 -- 0.84, similar to typical
values found for later-type spirals. The number of red globular clusters
associated with the bulges generally increases with the bulge luminosity,
similar to what is observed for elliptical galaxies, although the specific
frequency of bulge clusters is a factor of 2-3 lower for the lowest luminosity
bulges than for the higher luminosity bulges. We present a new empirical
relation between the fraction of red globular clusters and total bulge
luminosity based on the elliptical galaxies studied by ACSVCS (ACS Virgo
Cluster Survey), and discuss how this diagram can be used to assess the
importance that dissipative processes played in building spiral bulges. Our
results suggest a picture where dissipative processes, which are expected
during gas-rich major mergers, were more important for building luminous bulges
of Sa galaxies, whereas secular evolution may have played a larger role in
building lower-luminosity bulges in spirals.
