Abstract
We present the first application to density field reconstruction to a galaxy survey to undo the smoothing of the baryon acoustic oscillation (BAO) feature due to non-linear gravitational ...evolution and thereby improve the precision of the distance measurements possible. We apply the reconstruction technique to the clustering of galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) luminous red galaxy (LRG) sample, sharpening the BAO feature and achieving a 1.9 per cent measurement of the distance to z = 0.35. We update the reconstruction algorithm of Eisenstein et al. to account for the effects of survey geometry as well as redshift-space distortions and validate it on 160 LasDamas simulations. We demonstrate that reconstruction sharpens the BAO feature in the angle averaged galaxy correlation function, reducing the non-linear smoothing scale Σnl from 8.1 to 4.4 Mpc h
−1. Reconstruction also significantly reduces the effects of redshift-space distortions at the BAO scale, isotropizing the correlation function. This sharpened BAO feature yields an unbiased distance estimate (<0.2 per cent) and reduces the scatter from 3.3 to 2.1 per cent. We demonstrate the robustness of these results to the various reconstruction parameters, including the smoothing scale, the galaxy bias and the linear growth rate. Applying this reconstruction algorithm to the SDSS LRG DR7 sample improves the significance of the BAO feature in these data from 3.3σ for the unreconstructed correlation function to 4.2σ after reconstruction. We estimate a relative distance scale D
V
/r
s
to z = 0.35 of 8.88 ± 0.17, where r
s
is the sound horizon and is a combination of the angular diameter distance D
A and Hubble parameter H. Assuming a sound horizon of 154.25 Mpc, this translates into a distance measurement D
V
(z = 0.35) = 1.356 ± 0.025 Gpc. We find that reconstruction reduces the distance error in the DR7 sample from 3.5 to 1.9 per cent, equivalent to a survey with three times the volume of SDSS.
Abstract
We present results from fitting the baryon acoustic oscillation (BAO) signal in the correlation function obtained from the first application of density-field reconstruction to a galaxy ...redshift survey, namely the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) luminous red galaxy (LRG) catalogue. Reconstruction works to partially remove the effects of non-linear structure growth on the BAO by reconstructing the linear matter density field from the observed galaxy density field using the continuity equation. We also introduce more careful approaches for deriving a suitable covariance matrix and fitting model for galaxy correlation functions. Our covariance matrix technique guarantees smooth diagonal and off-diagonal terms by fitting a modified Gaussian covariance matrix to that calculated from mock catalogues. Our proposed fitting model is effective at removing broad-band effects such as redshift-space distortions, scale-dependent bias and any artefacts introduced by assuming the wrong model cosmology. These all aid in obtaining a more accurate measurement of the acoustic scale and its error. We validate these techniques on 160 mock catalogues derived from the LasDamas simulations in real and redshift space. We then apply these techniques to the DR7 LRG sample and find that the error on the acoustic scale decreases from ∼3.5 per cent before reconstruction to ∼1.9 per cent after reconstruction. We also see an increase in our BAO detection confidence from ∼3σ to ∼4σ after reconstruction with our confidence level in measuring the correct acoustic scale increasing from ∼3σ to ∼5σ. Using the mean of the acoustic scale probability distributions produced from our fits, we find D
v
/r
s
= 8.89 ± 0.31 before reconstruction and 8.88 ± 0.17 after reconstruction.
Abstract
We use the 2 per cent distance measurement from our reconstructed baryon acoustic oscillations (BAOs) signature using the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) luminous red ...galaxies from Padmanabhan et al. and Xu et al. combined with cosmic microwave background data from Wilkinson Microwave Anisotropy Probe (WMAP7) to measure parameters for various cosmological models. We find a 1.7 per cent measurement of H
0 = 69.8 ± 1.2 km s−1 Mpc−1 and a 5.0 per cent measurement of for a flat universe with a cosmological constant. These measurements of H
0 and Ωm are robust against a range of underlying models for the expansion history. We measure the dark energy equation of state parameter w = −0.97 ± 0.17, which is consistent with a cosmological constant. If curvature is allowed to vary, we find that the Universe is consistent with a flat geometry (ΩK = −0.004 ± 0.005). We also use a combination of the 6 Degree Field Galaxy Survey BAO data, WiggleZ Dark Energy Survey data, Type Ia supernovae data and a local measurement of the Hubble constant to explore cosmological models with more parameters. Finally, we explore the effect of varying the energy density of relativistic particles on the measurement of H
0.
We present new Near-Infrared Camera and Multi-Object Spectrometer and attitude control system observations of the quasar jet PKS 0637-752, and we use them, together with existing multiwavelength ...observations, to produce the most complete spectral coverage of the source to date. We explore the implications of these observations in the context of models for the jet X-ray emission. By relaxing the assumption of equipartition, we undertake an exhaustive study of the parameter space for external Compton off the cosmic microwave background (CMB) (EC/CMB) model. We find that the multiwavelength observations exclude a magnetic-field-dominated jet. Using the method proposed by Georganopoulos et al. for probing the jet matter content, we show that protons are practically needed for all jet configurations, extending a previous application of the method by Uchiyama et al. that was based on exploring three particular jet configurations. We also show that equipartition is the only configuration that can reproduce the observations and have one proton per radiating lepton. We finally present a rather model-independent argument that the jet has a spine-sheath flow pattern, with the spine being faster and emitting most of the infrared-optical X-ray emission.
ABSTRACT
We present measurements of galaxy clustering from the Baryon Oscillation Spectroscopic Survey (BOSS), which is part of the Sloan Digital Sky Survey III (SDSS‐III). These use the Data Release ...9 (DR9) CMASS sample, which contains 264 283 massive galaxies covering 3275 square degrees with an effective redshift z = 0.57 and redshift range 0.43 < z < 0.7. Assuming a concordance ΛCDM cosmological model, this sample covers an effective volume of 2.2 Gpc3, and represents the largest sample of the Universe ever surveyed at this density, n¯≈3×10−4h−3 Mpc 3. We measure the angle‐averaged galaxy correlation function and power spectrum, including density‐field reconstruction of the baryon acoustic oscillation (BAO) feature. The acoustic features are detected at a significance of 5σ in both the correlation function and power spectrum. Combining with the SDSS‐II luminous red galaxy sample, the detection significance increases to 6.7σ. Fitting for the position of the acoustic features measures the distance to z = 0.57 relative to the sound horizon DV/rs = 13.67 ± 0.22 at z = 0.57. Assuming a fiducial sound horizon of 153.19 Mpc, which matches cosmic microwave background constraints, this corresponds to a distance DV (z = 0.57) = 2094 ± 34 Mpc. At 1.7 per cent, this is the most precise distance constraint ever obtained from a galaxy survey. We place this result alongside previous BAO measurements in a cosmological distance ladder and find excellent agreement with the current supernova measurements. We use these distance measurements to constrain various cosmological models, finding continuing support for a flat Universe with a cosmological constant.
The baryon acoustic oscillation (BAO) feature in the clustering of matter in the universe serves as a robust standard ruler and hence can be used to map the expansion history of the universe. We use ...high force resolution simulations to analyze the effects of galaxy bias on the measurements of the BAO signal. We apply a variety of Halo Occupation Distributions (HODs) and produce biased mass tracers to mimic different galaxy populations. We investigate whether galaxy bias changes the nonlinear shifts on the acoustic scale relative to the underlying dark matter distribution presented by Seo et al. For the less biased HOD models (b < 3), we do not detect any shift in the acoustic scale relative to the no-bias case, typically 0.10% ? 0.10%. However, the most biased HOD models (b > 3) show a shift at moderate significance (0.79% ? 0.31% for the most extreme case). We test the one-step reconstruction technique introduced by Eisenstein et al. in the case of realistic galaxy bias and shot noise. The reconstruction scheme increases the correlation between the initial and final (z = 1) density fields, achieving an equivalent level of correlation at nearly twice the wavenumber after reconstruction. Reconstruction reduces the shifts and errors on the shifts. We find that after reconstruction the shifts from the galaxy cases and the dark matter case are consistent with each other and with no shift. The 1 Delta *s systematic errors on the distance measurements inferred from our BAO measurements with various HODs after reconstruction are about 0.07%-0.15%.
The baryon acoustic oscillation (BAO) feature in the clustering of matter in the universe serves as a robust standard ruler and hence can be used to map the expansion history of the universe. We use ...high force resolution simulations to analyze the effects of galaxy bias on the measurements of the BAO signal. We apply a variety of Halo Occupation Distributions (HODs) and produce biased mass tracers to mimic different galaxy populations. We investigate whether galaxy bias changes the non-linear shifts on the acoustic scale relative to the underlying dark matter distribution presented by Seo et al. (2009). For the less biased HOD models (b < 3), we do not detect any shift in the acoustic scale relative to the no-bias case, typically 0.10% ± 0.10%. However, the most biased HOD models (b > 3) show a shift at moderate significance (0.79% ± 0.31% for the most extreme case). We test the one-step reconstruction technique introduced by Eisenstein et al. (2007) in the case of realistic galaxy bias and shot noise. The reconstruction scheme increases the correlation between the initial and final (z = 1) density fields achieving an equivalent level of correlation at nearly twice the wavenumber after reconstruction. Reconstruction reduces the shifts and errors on the shifts. We find that after reconstruction the shifts from the galaxy cases and the dark matter case are consistent with each other and with no shift. The 1σ systematic errors on the distance measurements inferred from our BAO measurements with various HODs after reconstruction are about 0.07%-0.15%.
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