On the Use of the Number Count of Blue Horizontal--Branch Stars to Infer
  the Dominant Building Blocks of the Milky Way Halo
  The formation of the Milky Way stellar halo is thought to be the result of
merging and accretion of building blocks such as dwarf galaxies and massive
globular clusters. Recently, Deason et al. (2015) suggested that the Milky Way
outer halo formed mostly from big building blocks, such as dwarf spheroidal
galaxies, based on the similar number ratio of blue straggler (BS) stars to
blue horizontal-branch (BHB) stars. Here we demonstrate, however, that this
result is seriously biased by not taking into detailed consideration on the
formation mechanism of BHB stars from helium enhanced second-generation
population. In particular, the high BS-to-BHB ratio observed in the outer halo
fields is most likely due to a small number of BHB stars provided by GCs rather
than to a large number of BS stars. This is supported by our dynamical
evolution model of GCs which shows preferential removal of first generation
stars in GCs. Moreover, there are a sufficient number of outer halo GCs which
show very high BS-to-BHB ratio. Therefore, the BS-to-BHB number ratio is not a
good indicator to use in arguing that more massive dwarf galaxies are the main
building blocks of the Milky Way outer halo. Several lines of evidence still
suggest that GCs can contribute a significant fraction of the outer halo stars.
