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Register a new userDetection of the Baryon Acoustic Peak in the Large-Scale Correlation Function of SDSS Luminous Red Galaxies
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We present the large-scale correlation function measured from a spectroscopic sample of 46,748 luminous red galaxies from the Sloan Digital Sky Survey. The survey region covers 0.72 h^{-3} Gpc^3 over 3816 square degrees and 0.16<z<0.47, making it the best sample yet for the study of large-scale structure. We find a well-detected peak in the correlation function at 100h^{-1} Mpc separation that is an excellent match to the predicted shape and location of the imprint of the recombination-epoch acoustic oscillations on the low-redshift clustering of matter. This detection demonstrates the linear growth of structure by gravitational instability between z=1000 and the present and confirms a firm prediction of the standard cosmological theory. The acoustic peak provides a standard ruler by which we can measure the ratio of the distances to z=0.35 and z=1089 to 4% fractional accuracy and the absolute distance to z=0.35 to 5% accuracy. From the overall shape of the correlation function, we measure the matter density Omega_mh^2 to 8% and find agreement with the value from cosmic microwave background (CMB) anisotropies. Independent of the constraints provided by the CMB acoustic scale, we find Omega_m = 0.273 +- 0.025 + 0.123 (1+w_0) + 0.137 Omega_K. Including the CMB acoustic scale, we find that the spatial curvature is Omega_K=-0.010+-0.009 if the dark energy is a cosmological constant. More generally, our results provide a measurement of cosmological distance, and hence an argument for dark energy, based on a geometric method with the same simple physics as the microwave background anisotropies. The standard cosmological model convincingly passes these new and robust tests of its fundamental properties.
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We present the 3-point function xi_3 and Q_3=xi_3/xi_2^2 for a spectroscopic sample of luminous red galaxies (LRG) from SDSS DR6 & DR7. We find a strong (S/N$>$6) detection of $Q_3$ on scales of 55-125 Mpc/h, with a well defined peak around 105 Mpc/h in all xi_2, xi_3 and Q_3, in excellent agreement with the predicted shape and location of the imprint of the baryon acoustic oscillations (BAO). We use very large simulations to asses and test the significance of our measurement. Models without the BAO peak are ruled out by the $Q_3$ data with 99% confidence. Our measurements show the expected shape for Q_3 as a function of the triangular configuration. This provides a first direct measurement of the non-linear mode coupling coefficients of density and velocity fluctuations which, on these large scales, are independent of cosmic time, the amplitude of fluctuations or cosmological parameters. The location of the BAO peak in the data indicates Omega_m =0.28 pm 0.05 and Omega_B=0.079 pm 0.025 (h=0.70) after marginalization over spectral index (n_s=0.8-1.2) linear b_1 and quadratic c_2 bias,which are found to be in the range: b_1=1.7-2.2 and c_2=0.75-3.55. The data allows a hierarchical contribution from primordial non-Gaussianities in the range Q_3=0.55-3.35. These constraints are independent and complementary to the ones that can be obtained using the 2-point function, which are presented in a separate paper. This is the first detection of the shape of $Q_3$ on BAO scales, but our errors are shot-noise dominated and the SDSS volume is still relatively small, so there is ample room for future improvement in this type of measurements.
We analyse the large-scale angular correlation function (ACF) of the CMASS luminous galaxies (LGs), a photometric-redshift catalogue based on the Data Release 8 (DR8) of the Sloan Digital Sky Survey-III. This catalogue contains over $600 , , 000$ LGs in the range $0.45 leq z leq 0.65$, which was split into four redshift shells of constant width. First, we estimate the constraints on the redshift-space distortion (RSD) parameters $bsigma_8$ and $fsigma_8$, where $b$ is the galaxy bias, $f$ the growth rate and $sigma_8$ is the normalization of the perturbations, finding that they vary appreciably among different redshift shells, in agreement with previous results using DR7 data. When assuming constant RSD parameters over the survey redshift range, we obtain $fsigma_8 = 0.69 pm 0.21$, which agrees at the $1.5sigma$ level with Baryon Oscillation Spectroscopic Survey DR9 spectroscopic results. Next, we performed two cosmological analyses, where relevant parameters not fitted were kept fixed at their fiducial values. In the first analysis, we extracted the baryon acoustic oscillation peak position for the four redshift shells, and combined with the sound horizon scale from 7-year textit{Wilkinson Microwave Anisotropy Probe} $(WMAP7)$ to produce the constraints $Omega_{m}=0.249 pm 0.031$ and $w=-0.885 pm 0.145$. In the second analysis, we used the ACF full shape information to constrain cosmology using real data for the first time, finding $Omega_{m} = 0.280 pm 0.022$ and $f_b = Omega_b/Omega_m = 0.211 pm 0.026$. These results are in good agreement with $WMAP7$ findings, showing that the ACF can be efficiently applied to constrain cosmology in future photometric galaxy surveys.
The 2-point angular correlation function $w(theta)$ (2PACF), where $theta$ is the angular separation between pairs of galaxies, provides the transversal Baryon Acoustic Oscillation (BAO) signal almost model-independently. In this paper we use 409,337 luminous red galaxies in the redshift range $z = [0.440,0.555]$ obtained from the tenth data release of the Sloan Digital Sky Survey (SDSS DR10) to estimate $theta_{rm{BAO}}(z)$ from the 2PACF at six redshift {shells}. Since noise and systematics can hide the BAO signature in the $w - theta$ plane, we also discuss some criteria to localize the acoustic bump. We identify two sources of model-dependence in the analysis, namely, the value of the acoustic scale from Cosmic Microwave Background (CMB) measurements and the correction in the $theta_{rm{BAO}}(z)$ position due to projection effects. Constraints on the dark energy equation-of-state parameter w$(z)$ from the $theta_{rm{BAO}}(z)$ diagram are derived, as well as from a joint analysis with current CMB measurements. We find that the standard $Lambda$CDM model as well as some of its extensions are in good agreement with these $theta_{rm{BAO}}(z)$ measurements.
A new determination of the sound horizon scale in angular coordinates is presented. It makes use of ~ 0.6 x 10^6 Luminous Red Galaxies, selected from the Sloan Digital Sky Survey imaging data, with photometric redshifts. The analysis covers a redshift interval that goes from z=0.5 to z=0.6. We find evidence of the Baryon Acoustic Oscillations (BAO) signal at the ~ 2.3 sigma confidence level, with a value of theta_{BAO} (z=0.55) = (3.90 pm 0.38) degrees, including systematic errors. To our understanding, this is the first direct measurement of the angular BAO scale in the galaxy distribution, and it is in agreement with previous BAO measurements. We also show how radial determinations of the BAO scale can break the degeneracy in the measurement of cosmological parameters when they are combined with BAO angular measurements. The result is also in good agreement with the WMAP7 best-fit cosmology. We obtain a value of w_0 = -1.03 pm 0.16 for the equation of state parameter of the dark energy, Omega_M = 0.26 pm 0.04 for the matter density, when the other parameters are fixed. We have also tested the sensitivity of current BAO measurements to a time varying dark energy equation of state, finding w_a = 0.06 pm 0.22 if we fix all the other parameters to the WMAP7 best-fit cosmology.
The correlation function of the distribution of matter in the universe shows, at large scales, baryon acoustic oscillations, which were imprinted prior to recombination. This feature was first detected in the correlation function of the luminous red galaxies (LRG) of the Sloan Digital Sky Survey (SDSS). The final release (DR7) of the SDSS has been recently made available, and the useful volume is about two times bigger than in the old sample. We present here, for the first time, the redshift space correlation function of this sample at large scales together with that for one shallower, but denser volume-limited subsample drawn from the 2dF redshift survey. We test the reliability of the detection of the acoustic peak at about 100 Mpc/h and the behaviour of the correlation function at larger scales by means of careful estimation of errors. We confirm the presence of the peak in the latest data although broader than in previous detections.
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