  We report on the first application of the Alcock-Paczynski test to stacked
voids in spectroscopic galaxy redshift surveys.We use voids from the Sutter et
al. (2012) void catalog, which was derived from the Sloan Digital Sky Survey
Data Release 7 main sample and luminous red galaxy catalogs. The construction
of that void catalog removes potential shape measurement bias by using a
modified version of the ZOBOV algorithm and by removing voids near survey
boundaries and masks. We apply the shape-fitting procedure presented in Lavaux
& Wandelt (2012) to ten void stacks out to redshift z=0.36. Combining these
measurements, we determine the mean cosmologically induced "stretch" of voids
in three redshift bins, with 1-sigma errors of 5-15%. The mean stretch is
consistent with unity, providing no indication of a distortion induced by
peculiar velocities. While the statistical errors are too large to detect the
Alcock-Paczynski effect over our limited redshift range, this proof-of-concept
analysis defines procedures that can be applied to larger spectroscopic galaxy
surveys at higher redshifts to constrain dark energy using the expected
statistical isotropy of structures that are minimally affected by uncertainties
in galaxy velocity bias.

Cosmology and Nongalactic Astrophysics