  Assuming that center vortices are the confining gauge field configurations,
we argue that in gauges that are sensitive to the confining center vortex
degrees of freedom, and where the latter lie on the Gribov horizon, the
corresponding ghost form factor is infrared divergent. Furthermore, this
infrared divergence disappears when center vortices are removed from the
Yang-Mills ensemble. On the other hand, for gauge conditions which are
insensitive to center vortex degrees of freedom, the ghost form factor is
infrared finite and does not change (qualitatively) when center vortices are
removed. Evidence for our observation is provided from lattice calculations.
