Beyond BAO: improving cosmological constraints from BOSS with measurement of the void-galaxy cross-correlation

Abstract

We present a measurement of the anisotropic void-galaxy cross-correlation function in the CMASS galaxy sample of the BOSS DR12 data release. We perform a joint fit to the data for redshift space distortions (RSD) due to galaxy peculiar velocities and anisotropies due to the Alcock-Paczynski (AP) effect, for the first time using a velocity field reconstruction technique to remove the complicating effects of RSD in the void centre positions themselves. Fits to the void-galaxy function give a 1% measurement of the AP parameter combination \(D_A(z)H(z)/c = 0.436\pm0.005\) at redshift \(z=0.57\), where \(D_A\) is the angular diameter distance and \(H\) the Hubble parameter, exceeding the precision obtainable from baryon acoustic oscillations (BAO) by a factor of ~3.5 and free of systematic errors. From voids alone we also obtain a 12% measure of the growth rate, \(f\sigma_8(z=0.57)=0.050\pm0.06\). The parameter degeneracies are orthogonal to those obtained from galaxy clustering. Combining void information with that from BAO and galaxy RSD in the same CMASS sample, we measure \(D_A(0.57)/r_s=9.36\pm0.07\) (at 0.75% precision), \(H(0.57)r_s=(14.03\pm0.16)\;10^3\) kms\(^{-1}\)Mpc\(^{-1}\) (1.1%) and \(f\sigma_8=0.450\pm0.019\) (4.2%), consistent with cosmic microwave background (CMB) measurements from Planck. These represent a factor ~2 improvement in precision over previous results through the inclusion of void information. Fitting a flat cosmological constant LCDM model to these results in combination with Planck CMB data, we find up to a 16% reduction in uncertainties on \(H_0\) and \(\Omega_m\) compared to use of the corresponding BOSS consensus values. Constraints on extended models with non-flat geometry and a dark energy of state that differs from \(w=-1\) show an even greater improvement.