Clustering and Bias Measurements of SDSS Voids
  Using a void catalog from the SDSS survey, we present the first measurements
of void clustering and the corresponding void bias. Over the range 30-200 Mpc/h
the void auto-correlation is detected at 5-sigma significance for voids of
radius 15-20 Mpc/h. We also measure the void-galaxy cross-correlation at higher
signal-to-noise and compare the inferred void bias with the autocorrelation
results. Void bias is constant with scale for voids of a given size, but its
value falls from 5.6 +/- 1.0 to below zero as the void radius increases from 15
to 30 Mpc/h. The comparison of our measurements with carefully matched galaxy
mock catalogs, with no free parameters related to the voids, shows that model
predictions can be reliably made for void correlations. We study the dependence
of void bias on tracer density and void size with a view to future
applications. In combination with our previous lensing measurements of void
mass profiles, these clustering measurements provide another step towards using
voids as cosmological tracers.
