Beyond BAO: Improving cosmological constraints from BOSS data 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 DA(z)H(z)/c = 0.4367±0.0045 at redshift z = 0.57, where DA 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 10% measure of the growth rate, f σ8(z = 0.57) = 0.501 ± 0.051. 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 DA(0.57)/rs = 9.383 ± 0.077 (at 0.8% precision), H(0.57)rs = (14.05 ± 0.14) 10 3 kms −1 Mpc −1 (1%) and f σ8 = 0.453 ± 0.022 (4.9%), 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 ΛCDM model to these results in combination with Planck CMB data, we find up to an 11% reduction in uncertainties on H0 and Ωm 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.

The Gravitational Lensing Signatures of BOSS Voids in the Cosmic Microwave Background

“…We will assume that the effect of this on the calibration of our lensing templates is small and neglect it for the purposes of this work. Note that this is not an unreasonable approximation, as the most relevant parameter for determining the matter content of voids (and thus their lensing convergence κ) is σ 8 (Nadathur et al 2019b), and for the Takahashi simulations this is quite close to the Planck value σ 8 = 0.81 (Planck Collaboration et al 2018b).…”

“…These galaxies are biased tracers of the matter distribution, with a bias of b CMASS ∼ 2 (Alam et al 2017). Voids from this CMASS sample have previously been used in a variety of works (e.g., Nadathur 2016;Nadathur & Crittenden 2016;Hamaus et al 2016;Cai et al 2017;Nadathur et al 2019b).…”

“…We construct a void catalog from the CMASS data using the public REVOLVER void-finding code (Nadathur et al 2019b,c) 2 which is derived from the earlier ZOBOV algorithm (Neyrinck 2008). REVOLVER estimates the local galaxy overdensity field from the discrete galaxy distribution using a Voronoi tessellation field estimator (VTFE) technique including additional corrections for the CMASS selection function and the survey angular completeness and masks using appropriate weights, as described in detail in Nadathur & Hotchkiss (2014); Nadathur (2016); Nadathur et al (2019b). Locations of minima of this density field are identified as the sites of potential voids, the extents of which are determined by a watershed algorithm without pre-determined assumptions about void shapes.…”

“…We run REVOLVER on each of these MD-Patchy mocks in the same way as for the CMASS data sample, thus obtaining 2048 mock void catalogs that statistically closely match the BOSS voids. Similar mock void catalogs have been used for covariance estimation for void measurements by Nadathur & Crittenden (2016); Nadathur et al (2019b). These MD-Patchy voids have the same clustering properties as the BOSS voids and occupy the same section of the Planck sky defined by the BOSS footprint, but are uncorrelated with real structures and thus with the Planck κ map.…”

“…As a consequence of their low matter content, voids become dominated by dark energy at early times, and so are sensitive to its nature (Lee & Park 2009;Lavaux & Wandelt 2012;Bos et al 2012;Pisani et al 2015). The dynamics within voids can be accurately modelled by linear perturbation theory even on small scales (Cai et al 2016;Nadathur & Percival 2019;Nadathur et al 2019a), which provides a unique opportunity to measure the growth rate of structure through redshift-space distortions (RSD) in the distribution of galaxies around voids (some examples of these studies in survey data include Hamaus et al 2016;Hawken et al 2017;Achitouv et al 2017;Nadathur et al 2019b). A recent analysis by Nadathur et al (2019b) of the redshift-space void-galaxy correlation observed in the Baryon Oscillation Spectroscopic survey (BOSS; Dawson et al 2013) showed that in combination with galaxy clustering, this method reduces the uncertainty in the measurement of cosmological distance scales by 50% compared to previous results arXiv:1911.08475v2 [astro-ph.CO] 21 Jan 2020 based on baryon acoustic oscillations (Alam et al 2017).…”