How large are the globular cluster systems of early-type galaxies and do
  they scale with galaxy halo properties?
  The globular cluster systems of galaxies are well-known to extend to large
galactocentric radii. Here we quantify the size of GC systems using the half
number radius of 22 GC systems around early-type galaxies from the literature.
We compare GC system sizes to the sizes and masses of their host galaxies. We
find that GC systems typically extend to 4$\times$ that of the host galaxy
size, however this factor varies with galaxy stellar mass from about 3$\times$
for M$^{\ast}$ galaxies to 5$\times$ for the most massive galaxies in the
universe. The size of a GC system scales approximately linearly with the virial
radius (R$_{200}$) and with the halo mass (M$_{200}$) to the 1/3 power. The GC
system of the Milky Way follows the same relations as for early-type galaxies.
For Ultra Diffuse Galaxies their GC system size scales with halo mass and
virial radius as for more massive, larger galaxies. UDGs indicate that the
linear scaling of GC system size with stellar mass for massive galaxies
flattens out for low stellar mass galaxies. Our scalings are different to those
reported recently by Hudson \& Robison (2017).
