  M104 (NGC 4594, the Sombrero galaxy) is a mysterious massive early-type
galaxy that shows a dominant bulge and a prominent disk. However, the presence
of a halo in M104 has been elusive, and it is not yet known how M104 has
acquired such a peculiar structure. Using wide ($\sim2$ deg$^2$) and deep $ugi$
images of M104 obtained with the CFHT/MegaCam, we detect a large number of
globular clusters (GCs) found out to $R\approx35'$ ($\sim100$ kpc). The color
distribution of these GCs shows two subpopulations: a blue (metal-poor) system
and a red (metal-rich) system. The total number of GCs is estimated to be
$N_{GC}=1610\pm30$ and the specific frequency to be $S_{N}=1.8\pm0.1$. The
radial number density profile of the GCs is steep in the inner region at
$R<20'$, and becomes shallow in the outer region at $20'<R<35'$. The outer
region is dominated by blue GCs and is extended out to $R\approx35'$. This
shows clearly the existence of a giant metal-poor halo in M104. The inner
region is composed of a bulge hosting a disk, corresponding to a metal-rich
halo as seen in early-type galaxies. At least two clumps of blue GCs are found
in the outer region. One clump is overlapped with a faint stellar stream
located in the south west, indicating that it may be a remnant of a disrupted
dwarf galaxy. Our results imply that the metal-rich inner halo of M104 formed
first via major mergers, and the metal-poor outer halo grew via numerous minor
mergers.
