A measurement of the Alcock-Paczynski test using cosmic voids

We perform an Alcock-Paczyński test using stacked cosmic voids identified in the SDSS Data Release 7 main sample and Data Release 10 LOWZ and CMASS samples. We find ∼1,500 voids out to redshift 0.6 using a heavily modified and extended ver-sion of the watershed algorithm ZOBOV, which we call VIDE (Void IDentification and Examination). To assess the impact of peculiar velocities we use the mock void cat-alogs presented in Sutter et al. (2013). We find a constant uniform flattening of 14% along the line of sight when peculiar velocities are included. This flattening appears universal for all void sizes at all redshifts and for all tracer densities. We also use these mocks to identify an optimal stacking strategy. After correcting for systematic effects we find that our Alcock-Paczyński measurement leads to a preference of our best-fit value of ΩM ∼ 0.15 over ΩM = 1.0 by a likelihood ratio of 10. Likewise, we find a factor of 4.5 preference of the likelihood ratio for a ΛCDM ΩM = 0.3 model and a null measurement. Taken together, we find substantial evidence for the Alcock-Paczyński signal in our sample of cosmic voids. Our assessment using realistic mocks suggests that measurements with future SDSS releases and other surveys will provide tighter cosmological parameter constraints. The void-finding algorithm and catalogs used in this work will be made publicly available a