Five-percent measurements of the growth rate from simulation-based modelling of redshift-space clustering in BOSS LOWZ

Abstract

We use a simulation-based modelling approach to analyse the anisotropic clustering of the BOSS LOWZ sample over the radial range $0.4 \, h^{-1} \, \mathrm{Mpc}$ to $63 \, h^{-1} \, \mathrm{Mpc}$, significantly extending what is possible with a purely analytic modelling framework. Our full-scale analysis yields constraints on the growth of structure that are a factor of two more stringent than any other study on large scales at similar redshifts. We infer $f σ_8 = 0.471 \pm 0.024$ at $z \approx 0.25$, and $f σ_8 = 0.431 \pm 0.025$ at $z \approx 0.40$; the corresponding $Λ$CDM predictions of the Planck CMB analysis are $0.470 \pm 0.006$ and $0.476 \pm 0.005$, respectively. Our results are thus consistent with Planck, but also follow the trend seen in previous low-redshift measurements of $f σ_8$ falling slightly below the $Λ$CDM+CMB prediction. We find that small and large radial scales yield mutually consistent values of $f σ_8$, but there are $1-2.5 σ$ hints of small scales ($< 10 \, h^{-1} \, \mathrm{Mpc}$) preferring lower values for $f σ_8$ relative to larger scales. We analyse the constraining power of the full range of radial scales, finding that most of the multipole information about $fσ_8$ is contained in the scales $2 \, h^{-1} \, \mathrm{Mpc} \lesssim s \lesssim 20 \, h^{-1} \, \mathrm{Mpc}$. Evidently, once the cosmological information of the quasi-to-nonlinear regime has been harvested, large-scale modes contain only modest additional information about structure growth. Finally, we compare predictions for the galaxy-galaxy lensing amplitude of the two samples against measurements from SDSS and assess the lensing-is-low effect in light of our findings.