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Register a new userA 2.5% measurement of the growth rate from small-scale redshift space clustering of SDSS-III CMASS galaxies
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We perform the first fit to the anisotropic clustering of SDSS-III CMASS DR10 galaxies on scales of ~ 0.8 - 32 Mpc/h. A standard halo occupation distribution model evaluated near the best fit Planck LCDM cosmology provides a good fit to the observed anisotropic clustering, and implies a normalization for the peculiar velocity field of M ~ 2 x 10^13 Msun/h halos of f*sigma8(z=0.57) = 0.450 +/- 0.011. Since this constraint includes both quasi-linear and non-linear scales, it should severely constrain modified gravity models that enhance pairwise infall velocities on these scales. Though model dependent, our measurement represents a factor of 2.5 improvement in precision over the analysis of DR11 on large scales, f*sigma8(z=0.57) = 0.447 +/- 0.028, and is the tightest single constraint on the growth rate of cosmic structure to date. Our measurement is consistent with the Planck LCDM prediction of 0.480 +/- 0.010 at the ~1.9 sigma level. Assuming a halo mass function evaluated at the best fit Planck cosmology, we also find that 10% of CMASS galaxies are satellites in halos of mass M ~ 6 x 10^13 Msun/h. While none of our tests and model generalizations indicate systematic errors due to an insufficiently detailed model of the galaxy-halo connection, the precision of these first results warrant further investigation into the modeling uncertainties and degeneracies with cosmological parameters.
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General relativistic effects have long been predicted to subtly influence the observed large-scale structure of the universe. The current generation of galaxy redshift surveys have reached a size where detection of such effects is becoming feasible. In this paper, we report the first detection of the redshift asymmetry from the cross-correlation function of two galaxy populations which is consistent with relativistic effects. The dataset is taken from the Sloan Digital Sky Survey DR12 CMASS galaxy sample, and we detect the asymmetry at the $2.7sigma$ level by applying a shell-averaged estimator to the cross-correlation function. Our measurement dominates at scales around $10$ h$^{-1}$Mpc, larger than those over which the gravitational redshift profile has been recently measured in galaxy clusters, but smaller than scales for which linear perturbation theory is likely to be accurate. The detection significance varies by 0.5$sigma$ with the details of our measurement and tests for systematic effects. We have also devised two null tests to check for various survey systematics and show that both results are consistent with the null hypothesis. We measure the dipole moment of the cross-correlation function, and from this the asymmetry is also detected, at the $2.8 sigma$ level. The amplitude and scale-dependence of the clustering asymmetries are approximately consistent with the expectations of General Relativity and a biased galaxy population, within large uncertainties. We explore theoretical predictions using numerical simulations in a companion paper.
With the largest spectroscopic galaxy survey volume drawn from the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), we can extract cosmological constraints from the measurements of redshift and geometric distortions at quasi-linear scales (e.g. above 50 $h^{-1}$Mpc). We analyze the broad-range shape of the monopole and quadrupole correlation functions of the BOSS Data Release 12 (DR12) CMASS galaxy sample, at the effective redshift $z=0.59$, to obtain constraints on the Hubble expansion rate $H(z)$, the angular-diameter distance $D_A(z)$, the normalized growth rate $f(z)sigma_8(z)$, and the physical matter density $Omega_mh^2$. We obtain robust measurements by including a polynomial as the model for the systematic errors, and find it works very well against the systematic effects, e.g., ones induced by stars and seeing. We provide accurate measurements ${D_A(0.59)r_{s,fid}/r_s$ $rm Mpc$, $H(0.59)r_s/r_{s,fid}$ $km s^{-1} Mpc^{-1}$, $f(0.59)sigma_8(0.59)$, $Omega_m h^2}$ = ${1427pm26$, $97.3pm3.3$, $0.488 pm 0.060$, $0.135pm0.016}$, where $r_s$ is the comoving sound horizon at the drag epoch and $r_{s,fid}=147.66$ Mpc is the sound scale of the fiducial cosmology used in this study. The parameters which are not well constrained by our galaxy clustering analysis are marginalized over with wide flat priors. Since no priors from other data sets, e.g., cosmic microwave background (CMB), are adopted and no dark energy models are assumed, our results from BOSS CMASS galaxy clustering alone may be combined with other data sets, i.e., CMB, SNe, lensing or other galaxy clustering data to constrain the parameters of a given cosmological model. The uncertainty on the dark energy equation of state parameter, $w$, from CMB+CMASS is about 8 per cent. The uncertainty on the curvature fraction, $Omega_k$, is 0.3 per cent. We do not find deviation from flat $Lambda$CDM.
We measure the small-scale clustering of the Data Release 16 extended Baryon Oscillation Spectroscopic Survey Luminous Red Galaxy sample, corrected for fibre-collisions using Pairwise Inverse Probability weights, which give unbiased clustering measurements on all scales. We fit to the monopole and quadrupole moments and to the projected correlation function over the separation range $7-60,h^{-1}$Mpc with a model based on the Aemulus cosmological emulator to measure the growth rate of cosmic structure, parameterized by $fsigma_8$. We obtain a measurement of $fsigma_8(z=0.737)=0.408pm0.038$, which is $1.4sigma$ lower than the value expected from 2018 Planck data for a flat $Lambda$CDM model, and is more consistent with recent weak-lensing measurements. The level of precision achieved is 1.7 times better than more standard measurements made using only the large-scale modes of the same sample. We also fit to the data using the full range of scales $0.1-60,h^{-1}$Mpc modelled by the Aemulus cosmological emulator and find a $4.5sigma$ tension in the amplitude of the halo velocity field with the Planck+$Lambda$CDM model, driven by a mismatch on the non-linear scales. This may not be cosmological in origin, and could be due to a breakdown in the Halo Occupation Distribution model used in the emulator. Finally, we perform a robust analysis of possible sources of systematics, including the effects of redshift uncertainty and incompleteness due to target selection that were not included in previous analyses fitting to clustering measurements on small scales.
We perform a tomographic analysis of structure growth and expansion rate from the anisotropic galaxy clustering of the combined sample of Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12, which covers the redshift range of $0.2<z<0.75$. In order to extract the redshift information of anisotropic galaxy clustering, we analyse this data set in nine overlapping redshift slices in configuration space and perform the joint constraints on the parameters $(D_V, F_{mathrm{AP}}, fsigma_8)$ using the correlation function multipoles. The analysis pipeline is validated using the MultiDark-Patchy mock catalogues. We obtain a measurement precision of $1.5%-2.9%$ for $D_V$, $5.2%-9%$ for $F_{mathrm{AP}}$ and $13.3%-24%$ for $f sigma_8$, depending on the effective redshift of the slices. We report a joint measurement of $(D_V, F_{mathrm{AP}}, fsigma_8)$ with the full covariance matrix in nine redshift slices. We use our joint BAO and RSD measurement combined with external datasets to constrain the gravitational growth index $gamma$, and find $gamma=0.656 pm 0.057$, which is consistent with the $Lambda$CDM prediction within 95% CL.
We study the clustering of galaxies, as a function of their colour, from Data Release Ten (DR10) of the SDSS-III Baryon Oscillation Spectroscopic Survey. We select 122,967 galaxies with 0.43 < z < 0.7 into a Blue sample and 131,969 into a Red sample based on k+e corrected (to z=0.55) r-i colours and i band magnitudes. The samples are chosen to each contain more than 100,000 galaxies, have similar redshift distributions, and maximize the difference in clustering amplitude. The Red sample has a 40% larger bias than the Blue (b_Red/b_Blue = 1.39+-0.04), implying the Red galaxies occupy dark matter halos with an average mass that is 0.5 log Mo greater. Spherically averaged measurements of the correlation function, xi 0, and the power spectrum are used to locate the position of the baryon acoustic oscillation (BAO) feature of both samples. Using xi 0, we obtain distance scales, relative to our reference LCDM cosmology, of 1.010+-0.027 for the Red sample and 1.005+-0.031 for the Blue. After applying reconstruction, these measurements improve to 1.013+/-0.020 for the Red sample and 1.008+-0.026 for the Blue. For each sample, measurements of xi 0 and the second multipole moment, xi 2, of the anisotropic correlation function are used to determine the rate of structure growth, parameterized by fsigma 8. We find fsigma 8,Red = 0.511+-0.083, fsigma 8,Blue = 0.509+/-0.085, and fsigma 8,Cross = 0.423+-0.061 (from the cross-correlation between the Red and Blue samples). We use the covariance between the bias and growth measurements obtained from each sample and their cross-correlation to produce an optimally-combined measurement of fsigma 8,comb = 0.443+-0.055. In no instance do we detect significant differences in distance scale or structure growth measurements obtained from the Blue and Red samples.
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