BAO Feature Research Articles

Modeling the BAO feature in bispectrum

Abstract We investigate how well a simple leading order perturbation theory model of the bispectrum can fit the BAO feature in the measured bispectrum monopole of galaxies. Previous works showed that perturbative models of the galaxy bispectrum start failing at the wavenumbers of k ∼ 0.1h Mpc−1. We show that when the BAO feature in the bispectrum is separated it can be successfully modeled up to much higher wavenumbers. We validate our modeling on GLAM simulations that were run with and without the BAO feature in the initial conditions. We also quantify the amount of systematic error due to BAO template being offset from the true cosmology. We find that the systematic errors do not exceed 0.3 per cent for reasonable deviations of up to 3 per cent from the true value of the sound horizon.

Encrypted speech Biohashing authentication algorithm based on 4D hyperchaotic Bao system and feature fusion

Encrypted speech Biohashing authentication algorithm based on 4D hyperchaotic Bao system and feature fusion

The effect of quasar redshift errors on Lyman-α forest correlation functions

ABSTRACT Using synthetic Lyman-α forests from the Dark Energy Spectroscopic Instrument (DESI) survey, we present a study of the impact of errors in the estimation of quasar redshift on the Lyman-α correlation functions. Estimates of quasar redshift have large uncertainties of a few hundred km s−1 due to the broadness of the emission lines and the intrinsic shifts from other emission lines. We inject Gaussian random redshift errors into the mock quasar catalogues, and measure the auto-correlation and the Lyman-α-quasar cross-correlation functions. We find a smearing of the BAO feature in the radial direction, but changes in the peak position are negligible. However, we see a significant unphysical correlation for small separations transverse to the line of sight which increases with the amplitude of the redshift errors. We interpret this contamination as a result of the broadening of emission lines in the measured mean continuum, caused by quasar redshift errors, combined with the unrealistically strong clustering of the simulated quasars on small scales.

Can varying the gravitational constant alleviate the tensions?

Constraints on the cosmological concordance model parameters from observables at different redshifts are usually obtained using the locally measured value of the gravitational constant GN . Here we relax this assumption, by considering G as a free parameter, either constant over the redshift range or dynamical but limited to differ from fiducial value only above a certain redshift. Using CMB data and distance measurements from galaxy clustering BAO feature, we constrain the cosmological parameters, along with G, through a MCMC bayesian inference method. Furthermore, we investigate whether the tensions on the matter fluctuation σ8 and Hubble H0 parameter could be alleviated by this new variable. We used different parameterisations spanning from a constant G to a dynamical G. In all the cases investigated in this work we found no mechanism that alleviates the tensions when both CMB and BAO data are used with ξg = G / GN constrained to 1.0±0.04 (resp. ±0.01) in the constant (resp. dynamical) case. Finally, we studied the cosmological consequences of allowing a running of the spectral index, since the later is sensitive to a change in G. For the two parameterisations adopted, we found no significant changes to the previous conclusions.

Laguerre reconstruction of the BAO feature in halo-based mock galaxy catalogues

Fitting half-integer generalized Laguerre functions to the evolved, real-space dark matter and halo correlation functions provides a simple way to reconstruct their initial shapes. We show that this methodology also works well in a wide variety of realistic, assembly biased, velocity biased and redshift-space distorted mock galaxy catalogs. We use the linear point feature in the monopole of the redshift-space distorted correlation function to quantify the accuracy of our approach. We find that the linear point estimated from the mock galaxy catalogs is insensitive to the details of the biasing scheme at the subpercent level. However, the linear point scale in the nonlinear, biased, and redshift-space distorted field is systematically offset from its scale in the unbiased linear density fluctuation field by more than 1%. In the Laguerre reconstructed correlation function, this is reduced to sub-percent values, so it provides comparable accuracy and precision to methods that reconstruct the full density field before estimating the distance scale. The linear point in the reconstructed density fields provided by these other methods is likewise precise, accurate, and insensitive to galaxy bias. All reconstructions depend on some input parameters, and marginalizing over uncertainties in the input parameters required for reconstruction can degrade both accuracy and precision. The linear point simplifies the marginalization process, enabling more realistic estimates of the precision of the distance scale estimate for negligible additional computational cost. We show this explicitly for Laguerre reconstruction.

Laguerre reconstruction of the correlation function on baryon acoustic oscillation scales

The baryon acoustic oscillation feature can be used as a standard cosmological ruler. In practice, for subpercent level accuracy on the distance scale, it must be standardized. The physical reason why is understood, so we use this to develop an algorithm which improves the estimated scale. The algorithm exploits the fact that, over the range of scales where the initial correlation function is well fit by a polynomial, the leading order effects which distort the length of the ruler can be accounted for analytically. Tests of the method in numerical simulations show that it provides simple and fast reconstruction of the full shape of the BAO feature, as well as subpercent determination of the linear point in the correlation function of biased tracers with minimal assumptions about the underlying cosmological model or the nature of the observed tracers. Our results also suggest that, for least squares estimators of the correlation function, half-integer generalized Laguerre functions are a particularly useful choice.

The clustering of the SDSS-IV extended Baryon Oscillation Spectroscopic Survey quasar sample: testing observational systematics on the Baryon Acoustic Oscillation measurement

ABSTRACT Baryon Acoustic Oscillations (BAO) are considered to be a very robust standard ruler against various systematics. This premise has been tested against observational systematics, but not to the level required for the next generation of galaxy surveys such as the Dark Energy Spectroscopic Instrument (DESI) and Euclid. In this paper, we investigate the effect of observational systematics on the BAO measurement of the final sample of quasars from the extended Baryon Oscillation Spectroscopic Survey Data Release 16 in order to prepare and hone a similar analysis for upcoming surveys. We employ catalogues with various treatments of imaging systematic effects using linear and neural network-based non-linear approaches and consider how the BAO measurement changes. We also test how the variations to the BAO fitting model respond to the observational systematics. As expected, we confirm that the BAO measurements obtained from the DR16 quasar sample are robust against imaging systematics well within the statistical error, while reporting slightly modified constraints that shift the line-of-sight BAO signal by less than 1.1 per cent. We use realistic simulations with similar redshift and angular distributions as the DR16 sample to conduct statistical tests for validating the pipeline, quantifying the significance of differences, and estimating the expected bias on the BAO scale in future high-precision data sets. Although we find a marginal impact for the eBOSS QSO data, the work presented here is of vital importance for constraining the nature of dark energy with the BAO feature in the new era of big data cosmology.

The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: measurement of the BAO and growth rate of structure of the emission line galaxy sample from the anisotropic power spectrum between redshift 0.6 and 1.1

Abstract We analyse the large-scale clustering in Fourier space of emission line galaxies (ELG) from the Data Release 16 of the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey. The ELG sample contains 173,736 galaxies covering 1,170 square degrees in the redshift range 0.6 < z < 1.1. We perform a BAO measurement from the post-reconstruction power spectrum monopole, and study redshift space distortions (RSD) in the first three even multipoles. Photometric variations yield fluctuations of both the angular and radial survey selection functions. Those are directly inferred from data, imposing integral constraints which we model consistently. The full data set has only a weak preference for a BAO feature (1.4σ). At the effective redshift zeff = 0.845 we measure $D_{\rm V}(z_{\rm eff})/r_{\rm drag} = 18.33_{-0.62}^{+0.57}$, with DV the volume-averaged distance and rdrag the comoving sound horizon at the drag epoch. In combination with the RSD measurement, at zeff = 0.85 we find $f\sigma _8(z_{\rm eff}) = 0.289_{-0.096}^{+0.085}$, with f the growth rate of structure and σ8 the normalisation of the linear power spectrum, $D_{\rm H}(z_{\rm eff})/r_{\rm drag} = 20.0_{-2.2}^{+2.4}$ and DM(zeff)/rdrag = 19.17 ± 0.99 with DH and DM the Hubble and comoving angular distances, respectively. These results are in agreement with those obtained in configuration space, thus allowing a consensus measurement of fσ8(zeff) = 0.315 ± 0.095, $D_{\rm H}(z_{\rm eff})/r_{\rm drag} = 19.6_{-2.1}^{+2.2}$ and DM(zeff)/rdrag = 19.5 ± 1.0. This measurement is consistent with a flat ΛCDM model with Planck parameters.

Dark Energy Survey Year 1 results: measurement of the galaxy angular power spectrum

ABSTRACT We use data from the first-year observations of the DES collaboration to measure the galaxy angular power spectrum (APS), and search for its BAO feature. We test our methodology in a sample of 1800 DES Y1-like mock catalogues. We use the pseudo-Cℓ method to estimate the APS and the mock catalogues to estimate its covariance matrix. We use templates to model the measured spectra and estimate template parameters firstly from the Cℓ’s of the mocks using two different methods, a maximum likelihood estimator and a Markov Chain Monte Carlo, finding consistent results with a good reduced χ2. Robustness tests are performed to estimate the impact of different choices of settings used in our analysis. Finally, we apply our method to a galaxy sample constructed from DES Y1 data specifically for LSS studies. This catalogue comprises galaxies within an effective area of 1318 deg2 and 0.6 < z < 1.0. We find that the DES Y1 data favour a model with BAO at the $2.6 \sigma$ C.L. However, the goodness of fit is somewhat poor, with χ2/(d.o.f.) = 1.49. We identify a possible cause showing that using a theoretical covariance matrix obtained from Cℓ’s that are better adjusted to data results in an improved value of χ2/(dof) = 1.36 which is similar to the value obtained with the real-space analysis. Our results correspond to a distance measurement of DA(zeff = 0.81)/rd = 10.65 ± 0.49, consistent with the main DES BAO findings. This is a companion paper to the main DES BAO article showing the details of the harmonic space analysis.

A new scale in the bias expansion

The fact that the spatial nonlocality of galaxy formation is controlled by some short length scale like the Lagrangian radius is the cornerstone of the bias expansion for large-scale-structure tracers. However, the first sources of ionizing radiation between z≈ 15 and z≈ 6 are expected to have significant effects on the formation of galaxies we observe at lower redshift, at least on low-mass galaxies. These radiative-transfer effects introduce a new scale in the clustering of galaxies, i.e. the finite distance which ionizing radiation travels until it reaches a given galaxy. This mean free path can be very large, of order 100 h−1 Mpc. Consequently, higher-derivative terms in the bias expansion could turn out to be non-negligible even on these scales: treating them perturbatively would lead to a massive loss in predictivity and, for example, could spoil the determination of the BAO feature or constraints on the neutrino mass. Here, we investigate under what assumptions an explicit non-perturbative model of radiative-transfer effects can maintain the robustness of large-scale galaxy clustering as a cosmological probe.

Theoretical Systematics of Future Baryon Acoustic Oscillation Surveys

Future Baryon Acoustic Oscillation surveys aim at observing galaxy clustering over a wide range of redshift and galaxy populations at great precision, reaching tenths of a percent, in order to detect any deviation of dark energy from the $\LCDM$ model. We utilize a set of paired quasi-\Nb\, FastPM simulations that were designed to mitigate the sample variance effect on the BAO feature and evaluated the BAO systematics as precisely as $\sim 0.01\%$. We report anisotropic BAO scale shifts before and after density field reconstruction in the presence of redshift-space distortions over a wide range of redshift, galaxy/halo biases, and shot noise levels. We test different reconstruction schemes and different smoothing filter scales, and introduce physically-motivated BAO fitting models. For the first time, we derive a Galilean-invariant infrared resummed model for halos in real and redshift space. We test these models from the perspective of robust BAO measurements and non-BAO information such as growth rate and nonlinear bias. We find that pre-reconstruction BAO scale has moderate fitting-model dependence at the level of $0.1\%-0.2\%$ for matter while the dependence is substantially reduced to less than $0.07\%$ for halos. We find that post-reconstruction BAO shifts are generally reduced to below $0.1\%$ in the presence of galaxy/halo bias and show much smaller fitting model dependence. Different reconstruction conventions can potentially make a much larger difference on the line-of-sight BAO scale, upto $0.3\%$. Meanwhile, the precision (error) of the BAO measurements is quite consistent regardless of the choice of the fitting model or reconstruction convention.

The 2QDES Pilot: the luminosity and redshift dependence of quasar clustering

We present a new redshift survey, the 2dF Quasar Dark Energy Survey pilot (2QDESp), which consists of ${\approx}10000$ quasars from ${\approx}150$ deg$^2$ of the southern sky, based on VST-ATLAS imaging and 2dF/AAOmega spectroscopy. Combining our optical photometry with the WISE (W1,W2) bands we can select essentially contamination free quasar samples with $0.8{<}z{<}2.5$ and $g{<}20.5$. At fainter magnitudes, optical UVX selection is still required to reach our $g{\approx}22.5$ limit. Using both these techniques we observed quasar redshifts at sky densities up to $90$ deg$^{-2}$. By comparing 2QDESp with other surveys (SDSS, 2QZ and 2SLAQ) we find that quasar clustering is approximately luminosity independent, with results for all four surveys consistent with a correlation scale of $r_{0}{=}6.1{\pm}0.1 \: h^{-1}$Mpc, despite their decade range in luminosity. We find a significant redshift dependence of clustering, particularly when BOSS data with $r_{0}{=}7.3{\pm}0.1 \: h^{-1}$Mpc are included at $z{\approx}2.4$. All quasars remain consistent with having a single host halo mass of ${\approx}2{\pm}1{\times}10^{12} \: h^{-1}M_\odot$. This result implies that either quasars do not radiate at a fixed fraction of the Eddington luminosity or AGN black hole and dark matter halo masses are weakly correlated. No significant evidence is found to support fainter, X-ray selected quasars at low redshift having larger halo masses as predicted by the `hot halo' mode AGN model of Fanidakis et al. 2013. Finally, although the combined quasar sample reaches an effective volume as large as that of the original SDSS LRG sample, we do not detect the BAO feature in these data.

The MICE Grand Challenge lightcone simulation – II. Halo and galaxy catalogues

This is the second in a series of three papers in which we present an end-to-end simulation from the MICE collaboration, the MICE Grand Challenge (MICE-GC) run. The N-body contains about 70 billion dark-matter particles in a $(3 \, h^{-1} \, {\rm Gpc})^3$ comoving volume spanning 5 orders of magnitude in dynamical range. Here we introduce the halo and galaxy catalogues built upon it, both in a wide ($5000 \,{\rm deg}^2$) and deep ($z<1.4$) light-cone and in several comoving snapshots. Halos were resolved down to few $10^{11} \,h^{-1}\,{\rm M_{\odot}}$. This allowed us to model galaxies down to absolute magnitude M$_r<-18.9$. We used a new hybrid Halo Occupation Distribution and Abundance Matching technique for galaxy assignment. The catalogue includes the Spectral Energy Distributions of all galaxies. We describe a variety of halo and galaxy clustering applications. We discuss how mass resolution effects can bias the large scale $2$-pt clustering amplitude of poorly resolved halos at the $\lesssim 5\%$ level, and their $3$-pt correlation function. We find a characteristic scale dependent bias of $\lesssim 6\%$ across the BAO feature for halos well above $M_{\star}\sim 10^{12}\,h^{-1}\,{\rm M_{\odot}}$ and for LRG like galaxies. For halos well below $M_{\star}$ the scale dependence at $100\,{\rm Mpc} h^{-1}$ is $\lesssim 2\%$. Lastly we discuss the validity of the large-scale Kaiser limit across redshift and departures from it towards nonlinear scales. We make the current version of the light-cone halo and galaxy catalogue (MICECATv1.0) publicly available through a dedicated web portal, http://cosmohub.pic.es, to help develop and exploit the new generation of astronomical surveys.

The MICE grand challenge lightcone simulation – I. Dark matter clustering

We present a new N-body simulation from the MICE collaboration, the MICE Grand Challenge (MICE-GC), containing about 70 billion dark-matter particles in a (3 Gpc/h)^3 comoving volume. Given its large volume and fine spatial resolution, spanning over 5 orders of magnitude in dynamic range, it allows an accurate modeling of the growth of structure in the universe from the linear through the highly non-linear regime of gravitational clustering. We validate the dark-matter simulation outputs using 3D and 2D clustering statistics, and discuss mass-resolution effects in the non-linear regime by comparing to previous simulations and the latest numerical fits. We show that the MICE-GC run allows for a measurement of the BAO feature with percent level accuracy and compare it to state-of-the-art theoretical models. We also use sub-arcmin resolution pixelized 2D maps of the dark-matter counts in the lightcone to make tomographic analyses in real and redshift space. Our analysis shows the simulation reproduces the Kaiser effect on large scales, whereas we find a significant suppression of power on non-linear scales relative to the real space clustering. We complete our validation by presenting an analysis of the 3-point correlation function in this and previous MICE simulations, finding further evidence for mass-resolution effects. This is the first of a series of three papers in which we present the MICE-GC simulation, along with a wide and deep mock galaxy catalog built from it. This mock is made publicly available through a dedicated webportal, http://cosmohub.pic.es.

The bias of weighted dark matter haloes from peak theory

We give an analytical form for the weighted correlation function of peaks in a Gaussian random field. In a cosmological context, this approach strictly describes the formation bias and is the main result here. Nevertheless, we show its validity and applicability to the evolved cosmological density field and halo field, using Gaussian random field realisations and dark matter N-body numerical simulations. Using this result from peak theory we compute the bias of peaks (and dark matter halos) and show that it reproduces results from the simulations at the ${\mathcal O}(10\%)$ level. Our analytical formula for the bias predicts a scale-dependent bias with two characteristics: a broad band shape which, however, is most affected by the choice of weighting scheme and evolution bias, and a more robust, narrow feature localised at the BAO scale, an effect that is confirmed in simulations. This scale-dependent bias smooths the BAO feature but, conveniently, does not move it. We provide a simple analytic formula to describe this effect. We envision that our analytic solution will be of use for galaxy surveys that exploit galaxy clustering.

Photo-z quality cuts and their effect on the measured galaxy clustering

Photometric galaxy surveys are an essential tool to further our understanding of the large-scale structure of the universe, its matter and energy content and its evolution. These surveys necessitate the determination of the galaxy redshifts using photometric techniques (photo-z). Oftentimes, it is advantageous to remove from the galaxy sample those for which one suspects that the photo-z estimation might be unreliable. In this paper, we show that applying these photo-z quality cuts blindly can grossly bias the measured galaxy correlations within and across photometric redshift bins. We then extend the work of Ho et al. (2012) and Ross et al. (2011) to develop a simple and effective method to correct for this using the data themselves. Finally, we apply the method to the Mega-Z catalog, containing about a million luminous red galaxies in the redshift range 0.45 < z < 0.65. After splitting the sample into four \Delta z = 0.05 photo-z bins using the BPZ algorithm, we see how our corrections bring the measured galaxy auto- and cross-correlations into agreement with expectations. We then look for the BAO feature in the four bins, with and without applying the photo-z quality cuts, and find a broad agreement between the BAO scales extracted in both cases. Intriguingly, we observe a correlation between galaxy density and photo-z quality even before any photo-z quality cuts are applied. This may be due to uncorrected observational effects that result in correlated gradients across the sky of the galaxy density and the galaxy photo-z precision. Our correction procedure could also help to mitigate some of these systematic effects.

Skewness as a probe of baryon acoustic oscillations

In this study we show that the skewness S_3 of the cosmic density field contains a significant and potentially detectable and clean imprint of Baryonic Acoustic Oscillations. Although the BAO signal in the skewness has a lower amplitude than second order measures like the two-point correlation function and power spectrum, it has the advantage of a considerably lower sensitivity to systematic influences. Because it lacks a direct dependence on bias if this concerns simple linear bias, skewness will be considerably less beset by uncertainties due to galaxy bias. Also, it has a weaker sensitivity to redshift distortion effects. We use perturbation theory to evaluate the magnitude of the effect on the volume-average skewness, for various cosmological models. One important finding of our analysis is that the skewness BAO signal occurs at smaller scales than that in second order statistics. For an LCDM spectrum with WMAP7 normalization, the BAO feature has a maximum wiggle amplitude of ~3% and appears at a scale of ~82Mpc/h. We conclude that the detection of BAO wiggles in future extensive galaxy surveys via the skewness of the observed galaxy distribution may provide us with a useful, and potentially advantageous, measure of the nature of Dark Energy.

DETECTING BARYON ACOUSTIC OSCILLATIONS

Baryon Acoustic Oscillations are a feature imprinted in the galaxy distribution by acoustic waves traveling in the plasma of the early universe. Their detection at the expected scale in large-scale structures strongly supports current cosmological models with a nearly linear evolution from redshift approximately 1000, and the existence of dark energy. Besides, BAOs provide a standard ruler for studying cosmic expansion. In this paper we focus on methods for BAO detection using the correlation function measurement. For each method, we want to understand the tested hypothesis (the hypothesis H0 to be rejected) and the underlying assumptions. We first present wavelet methods which are mildly model-dependent and mostly sensitive to the BAO feature. Then we turn to fully model-dependent methods. We present the most often used method based on the chi^2 statistic, but we find it has limitations. In general the assumptions of the chi^2 method are not verified, and it only gives a rough estimate of the significance. The estimate can become very wrong when considering more realistic hypotheses, where the covariance matrix of the measurement depends on cosmological parameters. Instead we propose to use a new method based on two modifications: we modify the procedure for computing the significance and make it rigorous, and we modify the statistic to obtain better results in the case of varying covariance matrix. We verify with simulations that correct significances are different from the ones obtained using the classical chi^2 procedure. We also test a simple example of varying covariance matrix. In this case we find that our modified statistic outperforms the classical chi^2 statistic when both significances are correctly computed. Finally we find that taking into account variations of the covariance matrix can change both BAO detection levels and cosmological parameter constraints.

SDSS-III: MASSIVE SPECTROSCOPIC SURVEYS OF THE DISTANT UNIVERSE, THE MILKY WAY, AND EXTRA-SOLAR PLANETARY SYSTEMS

Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II), SDSS-III is a program of four spectroscopic surveys on three scientific themes: dark energy and cosmological parameters, the history and structure of the Milky Way, and the population of giant planets around other stars. In keeping with SDSS tradition, SDSS-III will provide regular public releases of all its data, beginning with SDSS DR8 (which occurred in Jan 2011). This paper presents an overview of the four SDSS-III surveys. BOSS will measure redshifts of 1.5 million massive galaxies and Lya forest spectra of 150,000 quasars, using the BAO feature of large scale structure to obtain percent-level determinations of the distance scale and Hubble expansion rate at z<0.7 and at z~2.5. SEGUE-2, which is now completed, measured medium-resolution (R=1800) optical spectra of 118,000 stars in a variety of target categories, probing chemical evolution, stellar kinematics and substructure, and the mass profile of the dark matter halo from the solar neighborhood to distances of 100 kpc. APOGEE will obtain high-resolution (R~30,000), high signal-to-noise (S/N>100 per resolution element), H-band (1.51-1.70 micron) spectra of 10^5 evolved, late-type stars, measuring separate abundances for ~15 elements per star and creating the first high-precision spectroscopic survey of all Galactic stellar populations (bulge, bar, disks, halo) with a uniform set of stellar tracers and spectral diagnostics. MARVELS will monitor radial velocities of more than 8000 FGK stars with the sensitivity and cadence (10-40 m/s, ~24 visits per star) needed to detect giant planets with periods up to two years, providing an unprecedented data set for understanding the formation and dynamical evolution of giant planet systems. (Abridged)

Large-scale BAO signatures of the smallest galaxies

Recent work has shown that at high redshift, the relative velocity between dark matter and baryonic gas is typically supersonic. This relative velocity suppresses the formation of the earliest baryonic structures like minihalos, and the suppression is modulated on large scales. This effect imprints a characteristic shape in the clustering power spectrum of the earliest structures, with significant power on ∼ 100 Mpc scales featuring highly pronounced baryon acoustic oscillations. The amplitude of these oscillations is orders of magnitude larger at z ∼ 20 than previously expected. This characteristic signature can allow us to distinguish the effects of minihalos on intergalactic gas at times preceding and during reionization. We illustrate this effect with the example of 21 cm emission and absorption from redshifts during and before reionization. This effect can potentially allow us to probe physics on kpc scales using observations on 100 Mpc scales.We present sensitivity forecasts for FAST and Arecibo. Depending onparameters, this enhanced structure may be detectable by Arecibo atz ∼ 15−20, and with appropriate instrumentation FAST could measurethe BAO power spectrum with high precision. In principle, this effectcould also pose a serious challenge for efforts to constrain darkenergy using observations of the BAO feature at low redshift.