We present new results for the three-point correlation function, ζ, measured as a function of scale, luminosity and colour from the final version of the 2dF Galaxy Redshift Survey (2dFGRS). The ...reduced three-point correlation function, Q3~ζ/ξ2, is estimated for different triangle shapes and sizes, employing a full covariance analysis. The form of Q3 is consistent with the expectations for the Λ cold dark matter model, confirming that the primary influence shaping the distribution of galaxies is gravitational instability acting on Gaussian primordial fluctuations. However, we find a clear offset in amplitude between Q3 for galaxies and the predictions for the dark matter. We are able to rule out the scenario in which galaxies are unbiased tracers of the mass at the 9σ level. On weakly non-linear scales, we can interpret our results in terms of galaxy bias parameters. We find a linear bias term that is consistent with unity, b1= 0.93+0.10-0.08 and a quadratic bias c2=b2/b1=-0.34+0.11-0.08. This is the first significant detection of a non-zero quadratic bias, indicating a small but important non-gravitational contribution to the three-point function. Our estimate of the linear bias from the three-point function is independent of the normalization of underlying density fluctuations, so we can combine this with the measurement of the power spectrum of 2dFGRS galaxies to constrain the amplitude of matter fluctuations. We find that the rms linear theory variance in spheres of radius 8 h−1 Mpc is σ8= 0.88+0.12-0.10, providing an independent confirmation of values derived from other techniques. On non-linear scales, where ξ > 1, we find that Q3 has a strong dependence on scale, colour and luminosity.
We explore the biasing in the clustering statistics of haloes as compared to dark matter (DM) in simulations. We look at the second- and third-order statistics at large scales of the (intermediate) ...MICEL1536 simulation and also measure directly the local bias relation h=f(δ) between DM fluctuations, δ, smoothed over a top-hat radius R
s at a point in the simulation and its corresponding tracer h (i.e. haloes) at the same point. This local relation can be Taylor expanded to define a linear (b
1) and non-linear (b
2) bias parameter. The values of b
1 and b
2 in the simulation vary with R
s approaching a constant value around R
s > 30-60 Mpc h
−1. We use the local relation to predict the clustering of the tracer in terms of the one of DM. This prediction works very well (about per cent level) for the halo 2-point correlation ξ(r
12) for r
12 > 15 Mpc h
−1, but only when we use the biasing values that we found at very large smoothing radii R
s > 30-60 Mpc h
−1. We find no effect from stochastic or next-to-leading-order terms in the f(δ) expansion. However, we do find some discrepancies in the 3-point function that needs further understanding. We also look at the clustering of the smoothed moments, the variance and skewness which are volume-average correlations and therefore include clustering from smaller scales. In this case, we find that both next-to-leading-order and discreteness corrections (to the local model) are needed at the 10-20 per cent level. Shot-noise can be corrected with a term
, where σ2
e < 1, that is, always smaller than the Poisson correction. We also compare these results with the peak-background split predictions from the measured halo mass function. We find 5-10 per cent systematic (and similar statistical) errors in the mass estimation when we use the halo model biasing predictions to calibrate the mass.
We cross-correlate the third-year Wilkinson Microwave Anisotropy Probe (WMAP) data with galaxy samples extracted from the SDSS DR4 (SDSS4) covering 13 per cent of the sky, increasing the volume ...sampled in previous analysis by a factor of 3.7. The new measurements confirm a positive cross-correlation with higher significance (total signal-to-noise ratio of about 4.7). The correlation as a function of angular scale is well fitted by the integrated Sachs–Wolfe (ISW) effect for Λ cold dark matter (ΛCDM) flat Friedmann–Robertson–Walker models with a cosmological constant. The combined analysis of different samples gives ΩΛ = 0.80–0.85 (68 per cent confidence level, CL) or 0.77–0.86 (95 per cent CL). We find similar best-fitting values for ΩΛ for different galaxy samples with median redshifts of z≃ 0.3 and z≃ 0.5, indicating that the data scale with redshift as predicted by the LCDM cosmology (with equation of state parameter w =−1). This agreement is not trivial, but cannot yet be used to break the degeneracy constraints in the w versus ΩΛ plane using only the ISW data.
ABSTRACT There is an overwhelming evidence that white dwarfs host planetary systems; revealed by the presence, disruption, and accretion of planetary bodies. A lower limit on the frequency of white ...dwarfs that host planetary material has been estimated to be ≃ 25–50 per cent; inferred from the ongoing or recent accretion of metals on to both hydrogen-atmosphere and warm helium-atmosphere white dwarfs. Now with the unbiased sample of white dwarfs observed by the Dark Energy Spectroscopic Instrument (DESI) survey in their Early Data Release (EDR), we have determined the frequency of metal enrichment around cool-helium atmosphere white dwarfs as 21 ± 3 per cent using a sample of 234 systems. This value is in good agreement with values determined from previous studies. With the current samples we cannot distinguish whether the frequency of planetary accretion varies with system age or host-star mass, but the DESI data release 1 will contain roughly an order of magnitude more white dwarfs than DESI EDR and will allow these parameters to be investigated.
We model the abundance of haloes in the ∼(3 Gpc h
−1)3 volume of the MICE Grand Challenge simulation by fitting the universal mass function with an improved Jackknife error covariance estimator that ...matches theory predictions. We present unifying relations between different fitting models and new predictions for linear (b
1) and non-linear (c
2 and c
3) halo clustering bias. Different mass function fits show strong variations in their performance when including the low mass range (M
h ≲ 3 × 1012 M⊙ h
−1) in the analysis. Together with fits from the literature, we find an overall variation in the amplitudes of around 10 per cent in the low mass and up to 50 per cent in the high mass (galaxy cluster) range (M
h > 1014 M⊙ h
−1). These variations propagate into a 10 per cent change in b
1 predictions and a 50 per cent change in c
2 or c
3. Despite these strong variations, we find universal relations between b
1 and c
2 or c
3 for which we provide simple fits. Excluding low-mass haloes, different models fitted with reasonable goodness in this analysis, show per cent level agreement in their b
1 predictions, but are systematically 5–10 per cent lower than the bias directly measured with two-point halo-mass clustering. This result confirms previous findings derived from smaller volumes (and smaller masses). Inaccuracies in the bias predictions lead to 5–10 per cent errors in growth measurements. They also affect any halo occupation distribution fitting or (cluster) mass calibration from clustering measurements.
Baryon Acoustic Oscillations (BAOs) provide a 'standard ruler' of known physical length, making it one of the most promising probes of the nature of dark energy (DE). The detection of BAOs as an ...excess of power in the galaxy distribution at a certain scale requires measuring galaxy positions and redshifts. 'Transversal' (or 'angular') BAOs measure the angular size of this scale projected in the sky and provide information about the angular distance. 'Line-of-sight' (or 'radial') BAOs require very precise redshifts, but provide a direct measurement of the Hubble parameter at different redshifts, a more sensitive probe of DE. The main goal of this paper is to show that it is possible to obtain photometric redshifts with enough precision ( sigma z ) to measure BAOs along the line of sight. There is a fundamental limitation as to how much one can improve the BAO measurement by reducing sigma z . We show that sigma z ~ 0.003(1 + z) is sufficient: a much better precision will produce an oversampling of the BAO peak without a significant improvement on its detection, while a much worse precision will result in the effective loss of the radial information. This precision in redshift can be achieved for bright, red galaxies, featuring a prominent 4000 A break, by using a filter system comprising about 40 filters, each with a width close to 100 A, covering the wavelength range from ~4000 to ~8000 A, supplemented by two broad-band filters similar to the Sloan Digital Sky Survey u and z bands. We describe the practical implementation of this idea, a new galaxy survey project, PAU16Physics of the Accelerating Universe (PAU): http://www.ice.cat/pau., to be carried out with a telescope/camera combination with an etendue about 20 m2 deg2, equivalent to a 2 m telescope equipped with a 6 deg2 field of view camera, and covering 8000 deg2 in the sky in four years. We expect to measure positions and redshifts for over 14 million red, early-type galaxies with L > L and iAB 22.5 in the redshift interval 0.1 < z < 0.9, with a precision sigma z < 0.003(1 + z). This population has a number density n 10 -3 Mpc -3 h 3 galaxies within the 9 Gpc3 h -3 volume to be sampled by our survey, ensuring that the error in the determination of the BAO scale is not limited by shot noise. By itself, such a survey will deliver precisions of order 5% in the dark-energy equation of state parameter w, if assumed constant, and can determine its time derivative when combined with future cosmic microwave background measurements. In addition, PAU will yield high-quality redshift and low-resolution spectroscopy for hundreds of millions of other galaxies, including a very significant high-redshift population. The data set produced by this survey will have a unique legacy value, allowing a wide range of astrophysical studies.
Abstract
We compare reduced three-point correlations Q of matter, haloes (as proxies for galaxies) and their cross-correlations, measured in a total simulated volume of ∼100 (h−1 Gpc)3, to ...predictions from leading order perturbation theory on a large range of scales in configuration space. Predictions for haloes are based on the non-local bias model, employing linear (b1) and non-linear (c2, g2) bias parameters, which have been constrained previously from the bispectrum in Fourier space. We also study predictions from two other bias models, one local (g2 = 0) and one in which c2 and g2 are determined by b1 via approximately universal relations. Overall, measurements and predictions agree when Q is derived for triangles with (r1r2r3)1/3 ≳60 h−1 Mpc, where r1 − 3 are the sizes of the triangle legs. Predictions for Qmatter, based on the linear power spectrum, show significant deviations from the measurements at the BAO scale (given our small measurement errors), which strongly decrease when adding a damping term or using the non-linear power spectrum, as expected. Predictions for Qhalo agree best with measurements at large scales when considering non-local contributions. The universal bias model works well for haloes and might therefore be also useful for tightening constraints on b1 from Q in galaxy surveys. Such constraints are independent of the amplitude of matter density fluctuation (σ8) and hence break the degeneracy between b1 and σ8, present in galaxy two-point correlations.
This paper presents a comparison of the predictions for the two- and three-point correlation functions of density fluctuations, ξ and ζ, in gravitational perturbation theory (PT) against large cold ...dark matter (CDM) simulations. This comparison is made possible for the first time on large weakly non-linear scales (>10 h−1 Mpc) thanks to the development of a new algorithm for estimating correlation functions for millions of points in only a few minutes. Previous studies in the literature comparing the PT predictions of the three-point statistics with simulations have focused mostly on Fourier space, angular space or smoothed fields. Results in configuration space, such as those presented here, were limited to small scales where leading-order PT gives a poor approximation. Here we also propose and apply a method for separating the first-order and subsequent contributions to PT by combining different output times from the evolved simulations. We find that in all cases there is a regime where simulations do reproduce the leading-order (tree-level) predictions of PT for the reduced three-point function Q3∼ζ/ξ2. For steeply decreasing correlations (such as the standard CDM model) deviations from the tree-level results are important even at relatively large scales, ≃20 Mpc h−1. On larger scales ξ goes to zero and the results are dominated by sampling errors. In more realistic models (such as the ΛCDM cosmology) deviations from the leading-order PT become important at smaller scales r≃10 Mpc h-1, although this depends on the particular three-point configuration. We characterize the range of validity of this agreement and show the behaviour of the next-order (one-loop) corrections.
Large-scale modes in the temperature anisotropy power spectrum Cl measured by the Wilkinson Microwave Anisotropy Probe (WMAP) seem to have lower amplitudes (C2, C3 and C4) than that expected in the ...so-called concordance Λ-cold dark matter (ΛCDM) model. In particular, the quadrupole C2 is reported to have a smaller value than allowed by cosmic variance. This has been interpreted as a possible indication of new physics. In this paper, we re-analyse the WMAP data using the two-point angular correlation and its higher-order moments. This method, which requires a full covariance analysis, is more direct and provides better sampling of the largest modes than the standard harmonic decomposition. We show that the WMAP data are in good agreement (≃30 per cent probability) with a ΛCDM model when the WMAP data are considered as a particular realization drawn from a set of realistic ΛCDM simulations with the corresponding covariance. This is also true for the higher-order moments, shown here up to sixth order, which are consistent with the Gaussian hypothesis. The sky mask plays a major role in assessing the significance of these agreements. We recover the best-fitting model for the low-order multipoles based on the two-point correlation with different assumptions for the covariance. Assuming that the observations are a fair sample of the true model, we find C2= 123 ± 233, C3= 217 ± 241 and C4= 212 ± 162 (in μK2). The errors increase by about a factor of 5 if we assume the ΛCDM model. If we exclude the Galactic plane ∼b∼ < 30 from our analysis, we recover very similar values within the errors (i.e. C2= 172, C3= 89, C4= 129). This indicates that the Galactic plane is not responsible for the lack of large-scale power in the WMAP data.
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