Non-linear corrections to the cosmological matter power spectrum and scale-dependent galaxy bias: implications for parameter estimation (original) (raw)
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A prescription for galaxy biasing evolution as a nuisance parameter
Monthly Notices of the Royal Astronomical Society, 2015
There is currently no consistent approach to modelling galaxy bias evolution in cosmological inference. This lack of a common standard makes the rigorous comparison or combination of probes difficult. We show that the choice of biasing model has a significant impact on cosmological parameter constraints for a survey such as the Dark Energy Survey (DES), considering the 2-point correlations of galaxies in five tomographic redshift bins. We find that modelling galaxy bias with a free biasing parameter per redshift bin gives a Figure of Merit (FoM) for Dark Energy equation of state parameters w 0 , w a smaller by a factor of 10 than if a constant bias is assumed. An incorrect bias model will also cause a shift in measured values of cosmological parameters. Motivated by these points and focusing on the redshift evolution of linear bias, we propose the use of a generalised galaxy bias which encompasses a range of bias models from theory, observations and simulations, b(z) = c + (b 0 − c)/D(z) α , where parameters c, b 0 and α depend on galaxy properties such as halo mass. For a DES-like galaxy survey we find that this model gives an unbiased estimate of w 0 , w a with the same number or fewer nuisance parameters and a higher FoM than a simple b(z) model allowed to vary in z-bins. We show how the parameters of this model are correlated with cosmological parameters. We fit a range of bias models to two recent datasets, and conclude that this generalised parameterisation is a sensible benchmark expression of galaxy bias on large scales.
Sensitivity of Cosmological Parameter Estimation to Nonlinear Prescription from Galaxy Clustering
The Astrophysical Journal
Next generation large scale surveys will probe the nonlinear regime with high resolution. Making viable cosmological inferences based on these observations requires accurate theoretical modeling of the mildly nonlinear regime. In this work we investigate the sensitivity of cosmological parameter measurements from future probes of galaxy clustering to the choice of nonlinear prescription up to k max = 0.3 h Mpc −1. In particular, we calculate the induced parameter bias when the mildly nonlinear regime is modeled by the Halofit fitting scheme. We find significant (∼ 5σ) bias for some parameters with a future Euclid-like survey. We also explore the contribution of different scales to the parameter estimation for different observational setups and cosmological scenarios, compared for the two nonlinear prescriptions of Halofit and EFTofLSS. We include in the analysis the free parameters of the nonlinear theory and a blind parametrization for the galaxy bias. We find that marginalization over these nuisance parameters significantly boosts the errors of the standard cosmological parameters. This renders the differences in the predictions of the various nonlinear prescriptions less effective when transferred to the parameter space. More accurate modeling of these nuisance parameters would therefore greatly enhance the cosmological gain from the mildly nonlinear regime.
Phys Rev D, 2005
We combine the constraints from the recent Ly-α forest analysis of the Sloan Digital Sky Survey (SDSS) and the SDSS galaxy bias analysis with previous constraints from SDSS galaxy clustering, the latest supernovae, and 1st year WMAP cosmic microwave background anisotropies. We find significant improvements on all of the cosmological parameters compared to previous constraints, which highlights the importance of combining Lyα forest constraints with other probes. Combining WMAP and the Lyα forest we find for the primordial slope ns = 0.98 ± 0.02. We see no evidence of running, dn/d ln k = −0.003 ± 0.010, a factor of 3 improvement over previous constraints. We also find no evidence of tensors, r < 0.36 (95% c.l.). Inflationary models predict the absence of running and many among them satisfy these constraints, particularly negative curvature models such as those based on spontaneous symmetry breaking. A positive correlation between tensors and primordial slope disfavors chaotic inflation type models with steep slopes: while the V ∝ φ 2 model is within the 2-sigma contour, V ∝ φ 4 is outside the 3-sigma contour. For the amplitude we find σ8 = 0.90 ± 0.03 from the Lyα forest and WMAP alone. We find no evidence of neutrino mass: for the case of 3 massive neutrino families with an inflationary prior, mν < 0.42eV and the mass of lightest neutrino is m1 < 0.13eV at 95% c.l. For the 3 massless + 1 massive neutrino case we find mν < 0.79eV for the massive neutrino, excluding at 95% c.l. all neutrino mass solutions compatible with the LSND results. We explore dark energy constraints in models with a fairly general time dependence of dark energy equation of state, finding Ω λ = 0.72 ± 0.02, w(z = 0.3) = −0.98 +0.10 −0.12 , the latter changing to w(z = 0.3) = −0.92 +0.09 −0.10 if tensors are allowed. We find no evidence for variation of the equation of state with redshift, w(z = 1) = −1.03 +0.21 −0.28. These results rely on the current understanding of the Lyα forest and other probes, which need to be explored further both observationally and theoretically, but extensive tests reveal no evidence of inconsistency among different data sets used here.
Physical Review D, 2005
We combine the constraints from the recent Ly-α forest analysis of the Sloan Digital Sky Survey (SDSS) and the SDSS galaxy bias analysis with previous constraints from SDSS galaxy clustering, the latest supernovae, and 1st year WMAP cosmic microwave background anisotropies. We find significant improvements on all of the cosmological parameters compared to previous constraints, which highlights the importance of combining Lyα forest constraints with other probes. Combining WMAP and the Lyα forest we find for the primordial slope ns = 0.98 ± 0.02. We see no evidence of running, dn/d ln k = −0.003 ± 0.010, a factor of 3 improvement over previous constraints. We also find no evidence of tensors, r < 0.36 (95% c.l.). Inflationary models predict the absence of running and many among them satisfy these constraints, particularly negative curvature models such as those based on spontaneous symmetry breaking. A positive correlation between tensors and primordial slope disfavors chaotic inflation type models with steep slopes: while the V ∝ φ 2 model is within the 2-sigma contour, V ∝ φ 4 is outside the 3-sigma contour. For the amplitude we find σ8 = 0.90 ± 0.03 from the Lyα forest and WMAP alone. We find no evidence of neutrino mass: for the case of 3 massive neutrino families with an inflationary prior, mν < 0.42eV and the mass of lightest neutrino is m1 < 0.13eV at 95% c.l. For the 3 massless + 1 massive neutrino case we find mν < 0.79eV for the massive neutrino, excluding at 95% c.l. all neutrino mass solutions compatible with the LSND results. We explore dark energy constraints in models with a fairly general time dependence of dark energy equation of state, finding Ω λ = 0.72 ± 0.02, w(z = 0.3) = −0.98 +0.10 −0.12 , the latter changing to w(z = 0.3) = −0.92 +0.09 −0.10 if tensors are allowed. We find no evidence for variation of the equation of state with redshift, w(z = 1) = −1.03 +0.21 −0.28 . These results rely on the current understanding of the Lyα forest and other probes, which need to be explored further both observationally and theoretically, but extensive tests reveal no evidence of inconsistency among different data sets used here.
Physical Review D
We study the accuracy with which cosmological parameters can be determined from real space power spectrum of matter density contrast at weakly nonlinear scales using analytical approaches. From power spectra measured in N -body simulations and using Markov chain Monte-Carlo technique, the best-fitting cosmological input parameters are determined with several analytical methods as a theoretical template, such as the standard perturbation theory, the regularized perturbation theory, and the effective field theory. We show that at redshift 1, all two-loop level calculations can fit the measured power spectrum down to scales k ∼ 0.2 h Mpc −1 and cosmological parameters are successfully estimated in an unbiased way. Introducing the Figure of bias (FoB) and Figure of merit (FoM) parameter, we determine the validity range of those models and then evaluate their relative performances. With one free parameter, namely the damping scale, the regularized perturbation theory is found to be able to provide the largest FoM parameter while keeping the FoB in the acceptance range. PACS numbers: 98.80.-k, 98.80.Es
Journal of Cosmology and Astroparticle Physics, 2012
We investigate the accuracy of Eulerian perturbation theory for describing the matter and galaxy power spectra in real and redshift space in light of future observational probes for precision cosmology. Comparing the analytical results with a large suite of Nbody simulations (160 independent boxes of 13.8 (Gpc/h) 3 volume each, which are publicly available), we find that re-summing terms in the standard perturbative approach predicts the real-space matter power spectrum with an accuracy of 2% for k ≤ 0.20 h/Mpc at redshifts z 1.5. This is obtained following the widespread technique of writing the resummed propagator in terms of 1-loop contributions. We show that the accuracy of this scheme increases by considering higher-order terms in the resummed propagator. By combining resummed perturbation theories with several models for the mappings from real to redshift space discussed in the literature, the multipoles of the dark-matter power spectrum can be described with sub-percent deviations from N-body results for k ≤ 0.15 h/Mpc at z 1. As a consequence, the logarithmic growth rate, f , can be recovered with sub-percent accuracy on these scales. Extending the models to massive dark-matter haloes in redshift space, our results describe the monopole term from N-body data within 2% accuracy for scales k ≤ 0.15 h/Mpc at z 0.5; here f can be recovered within < 5% when the halo bias is known. We conclude that these techniques are suitable to extract cosmological information from future galaxy surveys.
Biases on cosmological parameter estimators from galaxy cluster number counts
Journal of Cosmology and Astroparticle Physics, 2014
The abundance of galaxy clusters is becoming a standard cosmological probe. In particular, Sunyaev-Zel'dovich (SZ) surveys are promising probes of the Dark Energy equation of state, given their ability to find distant clusters and provide estimates for their mass. However, current SZ catalogs contain tens to hundreds of objects. In this case, it is not guaranteed that maximum likelihood estimators of cosmological parameters are unbiased. In this work
Cosmological parameters degeneracies and non-Gaussian halo bias
Journal of Cosmology and Astroparticle Physics, 2010
We study the impact of the cosmological parameters uncertainties on the measurements of primordial non-Gaussianity through the large-scale non-Gaussian halo bias effect. While this is not expected to be an issue for the standard LCDM model, it may not be the case for more general models that modify the large-scale shape of the power spectrum. We consider the so-called local non-Gaussianity model and forecasts from planned surveys, alone and combined with a Planck CMB prior. In particular, we consider EUCLID- and LSST-like surveys and forecast the correlations among frmNLf_{\rm NL}frmNL and the running of the spectral index alphas\alpha_salphas, the dark energy equation of state www, the effective sound speed of dark energy perturbations c2sc^2_sc2s, the total mass of massive neutrinos Mnu=summnuM_\nu=\sum m_\nuMnu=summnu, and the number of extra relativistic degrees of freedom NnurelN_\nu^{rel}Nnurel. Neglecting CMB information on frmNLf_{\rm NL}frmNL and scales k>0.03hk > 0.03 hk>0.03h/Mpc, we find that, if NnurmrelN_\nu^{\rm rel}Nnurmrel is assumed to be known, the uncertainty on cosmological parameters increases the error on frmNLf_{\rm NL}frmNL by 10 to 30% depending on the survey. Thus the frmNLf_{\rm NL}frmNL constraint is remarkable robust to cosmological model uncertainties. On the other hand, if NnurmrelN_\nu^{\rm rel}Nnurmrel is simultaneously constrained from the data, the frmNLf_{\rm NL}frmNL error increases by sim80\sim 80%sim80. Finally, future surveys which provide a large sample of galaxies or galaxy clusters over a volume comparable to the Hubble volume can measure primordial non-Gaussianity of the local form with a marginalized 1--$\sigma$ error of the order DeltafrmNLsim2−5\Delta f_{\rm NL} \sim 2-5DeltafrmNLsim2−5, after combination with CMB priors for the remaining cosmological parameters. These results are competitive with CMB bispectrum constraints achievable with an ideal CMB experiment.
Galaxy Bias in Quintessence Cosmological Models
The Astrophysical Journal, 2003
We derive the evolution of the linear bias factor, b(z), in cosmological models driven by an exotic fluid with an equation of state: p x = wρ x , where −1 ≤ w < 0 (quintessence). Our aim is to put constrains on different cosmological and biasing models by combining the recent observational clustering results of optical (2dF) galaxies (Hawkings et al.) with those predicted by the models. We find that our bias model when fitted to the 2dF clustering results predicts different bias evolution for different values of w. The models that provide the weak biasing (b • ∼ 1.1) of optical galaxies found in many recent observational studies are flat, Ω m = 0.3 with w ≤ −0.9. These models however, predict a weak redshift evolution of b(z), not corroborated by N-body simulations.