The Aemulus Project V: Cosmological constraint from small-scale clustering of BOSS galaxies

Abstract

We analyze clustering measurements of BOSS galaxies using a simulation-based emulator of two-point statistics. We focus on the monopole and quadrupole of the redshift-space correlation function, and the projected correlation function, at scales of 0.1 ∼ 60 h −1 Mpc. Although our simulations are based on wCDM with general relativity (GR), we include a scaling parameter of the halo velocity field, γ f , defined as the amplitude of the halo velocity field relative to the GR prediction. We divide the BOSS data into three redshift bins. After marginalizing over other cosmological parameters, galaxy bias parameters, and the velocity scaling parameter, we find f σ 8 (z = 0.25) = 0.404 ± 0.03, f σ 8 (z = 0.4) = 0.444 ± 0.025 and f σ 8 (z = 0.55) = 0.385 ± 0.019. Compared with Planck observations using a flat ΛCDM model, our results are lower by 2.29σ, 1.3σ and 4.58σ respectively. These results are consistent with other recent simulation-based results at non-linear scales, including weak lensing measurements of BOSS LOWZ galaxies, two-point clustering of eBOSS LRGs, and an independent clustering analysis of BOSS LOWZ. All these results are generally consistent with a combination of γ 1/2 f σ 8 ≈ 0.75. We note, however, that the BOSS data is well fit assuming GR, i.e. γ f = 1. We cannot rule out an unknown systematic error in the galaxy bias model at non-linear scales, but near-future data and modeling will enhance our understanding of the galaxy-halo connection, and provide a strong test of new physics beyond the standard model.

Stringent $σ_8$ constraints from small-scale galaxy clustering using a hybrid MCMC+emulator framework

“…However, there is still some disagreement amongst the small-scale analyses despite a qualitative agreement in favoring a low 𝑓 𝜎 8 relative to Planck. Our results are statistically consistent with all other small-scale analyses except for the highest redshift bin of Zhai et al (2022), which finds a particularly low 𝑓 𝜎 8 that is in ∼ 2.9𝜎 tension with our results. A full exploration of this disagreement is beyond the scope of this paper, but is necessary to ensure small-scale simulation-based analyses account for all the necessary systematics.…”

“…The authors analyzed the small-scale RSD of a small sample of BOSS LOWZ LRGs and found constraints competitive with other small-scale analyses, while including a concentration-based prescription of secondary bias. Zhai et al (2022) and Chapman et al (2021) respectively analyzed the small-scale clusteirng of BOSS and eBOSS LRGs with an emulator built on the A simulation suite (DeRose et al 2019).…”

“…The issue of sparse cosmology sampling can be addressed with interpolative surrogate models known as emulators, as demonstrated with various degrees of success in recent studies (e.g. Heitmann et al 2009;Lawrence et al 2010;Heitmann et al 2014;Zhai et al 2019Zhai et al , 2022Lange et al 2019Lange et al , 2021Kobayashi et al 2021). These emulator models utilize flexible parametrized models such as polynomial expansions and Gaussian processes to interpolate between the model predictions at the available cosmologies to enable dense sampling of the cosmology likelihood space, but at the cost of additional errors due to uncertainties in the model.…”

Going Beyond the Galaxy Power Spectrum: an Analysis of BOSS Data with Wavelet Scattering Transforms

“…( 35) and the fact that the Hubble constant was not explicitly varied in our analysis, but was rather derived from a fixed θ 17 . This is also the case when attempting to compare against recent BOSS analyses using emulators of the redshift-space power spectrum [126] or the correlation function [90,119], with the additional difference that the correlation function analyses focused on much smaller scales than the ones we worked with. It should be also noted that the 1σ errors reported above are purely statistical, since we did not attempt to quantify how the various systematics and approximations adopted by our analysis would affect the final results.…”

“…[90] for a recent BOSS re-analysis using an ABACUS-trained emulator), the construction of an actual WST emulator will soon be possible in future work. Finally, we clarify that, even though a wide variety of approaches exist for a more accurate modeling of the cosmological dependence of the galaxy power spectrum or correlation function (e.g., perturbation theory [20, 76-78, 109, 110]) or emulators [90,103,[117][118][119]), we use the model from Eq. ( 35) for the power spectrum, as well, in order to guarantee a fair comparison against the performance of the WST, which is the ultimate purpose of this work.…”