The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: cosmological analysis of the DR12 galaxy sample

We present cosmological results from the final galaxy clustering dataset of the Baryon Oscillation Spectroscopic Survey, part of the SloanDigital Sky Survey III. Our combined galaxy sample comprises 1.2 millionmassive galaxies over an effective area of 9329 deg² andvolume of 18.7 Gpc³, divided into three partially overlappingredshift slices centred at effective redshifts 0.38, 0.51 and 0.61. Wemeasure the angular diameter distance D_M and Hubble parameterH from the baryon acoustic oscillation (BAO) method, in combination witha cosmic microwave background prior on the sound horizon scale, afterapplying reconstruction to reduce non-linear effects on the BAO feature.Using the anisotropic clustering of the pre-reconstruction densityfield, we measure the product D_MH from the Alcock-Paczynski(AP) effect and the growth of structure, quantified byfσ₈(z), from redshift-space distortions (RSD). Wecombine individual measurements presented in seven companion papers intoa set of consensus values and likelihoods, obtaining constraints thatare tighter and more robust than those from any one method; inparticular, the AP measurement from sub-BAO scales sharpens constraintsfrom post-reconstruction BAOs by breaking degeneracy betweenD_M and H. Combined with Planck 2016 cosmic microwavebackground measurements, our distance scale measurements simultaneouslyimply curvature Ω_K = 0.0003 ± 0.0026 and a darkenergy equation-of-state parameter w = -1.01 ± 0.06, in strongaffirmation of the spatially flat cold dark matter (CDM) model with acosmological constant (ΛCDM). Our RSD measurements offσ₈, at 6 per cent precision, are similarly consistentwith this model. When combined with supernova Ia data, we findH₀ = 67.3 ± 1.0 km s^-1 Mpc^-1even for our most general dark energy model, in tension with some directmeasurements. Adding extra relativistic species as a degree of freedomloosens the constraint only slightly, to H₀ = 67.8 ±1.2 km s^-1 Mpc^-1. Assuming flat ΛCDM, wefind Ω_m = 0.310 ± 0.005 and H₀ = 67.6± 0.5 km s^-1 Mpc^-1, and we find a 95 percent upper limit of 0.16 eV c^-2 on the neutrino mass sum.