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تسجيل مستخدم جديدConstraints on primordial non-Gaussianity from WMAP7 and Luminous Red Galaxies power spectrum and forecast for future surveys
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We place new constraints on the primordial local non-Gaussianity parameter f_NL using recent Cosmic Microwave Background anisotropy and galaxy clustering data. We model the galaxy power spectrum according to the halo model, accounting for a scale dependent bias correction proportional to f_NL/k^2. We first constrain f_NL in a full 13 parameters analysis that includes 5 parameters of the halo model and 7 cosmological parameters. Using the WMAP7 CMB data and the SDSS DR4 galaxy power spectrum, we find f_NL=171pm+140 at 68% C.L. and -69<f_NL<+492 at 95% C.L.. We discuss the degeneracies between f_NL and other cosmological parameters. Including SN-Ia data and priors on H_0 from Hubble Space Telescope observations we find a stronger bound: -35<f_NL<+479 at 95% C.L.. We also fit the more recent SDSS DR7 halo power spectrum data finding, for a Lambda-CDM+f_NL model, f_NL=-93pm128 at 68% C.L. and -327<f_{NL}<+177 at 95% C.L.. We finally forecast the constraints on f_NL from future surveys as EUCLID and from CMB missions as Planck showing that their combined analysis could detect f_NLsim 5.
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We study the constraining power on primordial non-Gaussianity of future surveys of the large-scale structure of the Universe for both near-term surveys (such as the Dark Energy Survey - DES) as well as longer term projects such as Euclid and WFIRST.
Specifically we perform a Fisher matrix analysis forecast for such surveys, using DES-like and Euclid-like configurations as examples, and take account of any expected photometric and spectroscopic data. We focus on two-point statistics and we consider three observables: the 3D galaxy power spectrum in redshift space, the angular galaxy power spectrum, and the projected weak-lensing shear power spectrum. We study the effects of adding a few extra parameters to the basic LCDM set. We include the two standard parameters to model the current value for the dark energy equation of state and its time derivative, w_0, w_a, and we account for the possibility of primordial non-Gaussianity of the local, equilateral and orthogonal types, of parameter fNL and, optionally, of spectral index n_fNL. We present forecasted constraints on these parameters using the different observational probes. We show that accounting for models that include primordial non-Gaussianity does not degrade the constraint on the standard LCDM set nor on the dark-energy equation of state. By combining the weak lensing data and the information on projected galaxy clustering, consistently including all two-point functions and their covariance, we find forecasted marginalised errors sigma (fNL) ~ 3, sigma (n_fNL) ~ 0.12 from a Euclid-like survey for the local shape of primordial non-Gaussianity, while the orthogonal and equilateral constraints are weakened for the galaxy clustering case, due to the weaker scale-dependence of the bias. In the lensing case, the constraints remain instead similar in all configurations.
We investigate how well future large-scale radio surveys could measure different shapes of primordial non-Gaussianity; in particular we focus on angle-dependent non-Gaussianity arising from primordial anisotropic sources, whose bispectrum has an angl
e dependence between the three wavevectors that is characterized by Legendre polynomials $mathcal{P}_L$ and expansion coefficients $c_L$. We provide forecasts for measurements of galaxy power spectrum, finding that Large-Scale Structure (LSS) data could allow measurements of primordial non-Gaussianity competitive or improving upon current constraints set by CMB experiments, for all the shapes considered. We argue that the best constraints will come from the possibility to assign redshift information to radio galaxy surveys, and investigate a few possible scenarios for the EMU and SKA surveys. A realistic (futuristic) modeling could provide constraints of $f_{rm NL}^{rm loc} approx 1 (0.5)$ for the local shape, $f_{rm NL}$ of $mathcal{O}(10) (mathcal{O}(1))$ for the orthogonal, equilateral and folded shapes, and $c_{L=1} approx 80 (2)$, $c_{L=2} approx 400 (10)$ for angle-dependent non-Gaussianity. The more futuristic forecasts show the potential of LSS analyses to considerably improve current constraints on non-Gaussianity, and so on models of the primordial Universe. Finally, we find the minimum requirements that would be needed to reach $sigma(c_{L=1})=10$, which can be considered as a typical (lower) value predicted by some (inflationary) models.
Extracting the bispectrum information from the large scale structure observations is challenging due to the complex models and the computational costs to measure the signal and its covariance. Recently, the skew spectrum was proposed to access parts
of the bispectrum information with a more effective way and has been confirmed it can provide complementary information to that enclosed in the power spectrum measurements. In this work, we generalize the theory to apply the multitracer technique and explore its ability to constrain the local type primordial non-Gaussianity. Using the spectra and their covariance estimated from $N$-body simulations, we find the multitracer approach is effective to reduce the cosmic variance noise. The $1sigma$ marginalized errors for $b_1^2A_s, n_s$ and $f_{rm NL}^{rm loc}$ are reduced by 50%, 52% and 73% comparing with the results using only power spectrum obtained from a single tracer. It indicate that both the skew spectrum and the multitracer technique are useful to constrain the primordial non-Gaussianity with the forthcoming wide-field galaxy surveys.
After reionisation, the 21cm emission line of neutral hydrogen within galaxies provides a tracer of dark matter. Next-generation intensity mapping surveys, with the SKA and other radio telescopes, will cover large sky areas and a wide range of redshi
fts, facilitating their use as probes of primordial non-Gaussianity. {Previous works have shown that the bispectrum can achieve tight constraints on primordial non-Gaussianity with future surveys that are purposely designed for intensity mapping in interferometer mode}. Here we investigate the constraints attainable from surveys operating in single-dish mode, rev{using the combined power spectrum and bispectrum signal}. In the case of the power spectrum, single-dish surveys typically outperform interferometer surveys. We find that the reverse holds for the bispectrum: single-dish surveys are not competitive with surveys designed for interferometer mode.
We derive robust constraints on primordial non-Gaussianity (PNG) using the clustering of 800,000 photometric quasars from the Sloan Digital Sky Survey in the redshift range $0.5<z<3.5$. These measurements rely on the novel technique of {it extended m
ode projection} to control the impact of spatially-varying systematics in a robust fashion, making use of blind analysis techniques. This allows the accurate measurement of quasar halo bias at the largest scales, while discarding as little as possible of the data. The standard local-type PNG parameters $f_mathrm{NL}$ and $g_mathrm{NL}$ both imprint a $k^{-2}$ scale-dependent effect in the bias. Constraining these individually, we obtain $-49<f_mathrm{NL}<31$ and $-2.7times10^5<g_mathrm{NL}<1.9times10^5$, while their joint constraints lead to $-105<f_mathrm{NL}<72$ and $-4.0times10^5<g_mathrm{NL}<4.9times10^5$ (all at 95% CL) . Introducing a running parameter $n_{f_mathrm{NL}}$ to constrain $b(k) propto k^{-2+n_{f_mathrm{NL}}}$ and a generalised PNG amplitude $tilde{f}_mathrm{NL}$, we obtain $-45.5 exp({3.7, n_{f_mathrm{NL}}}) < tilde{f}_mathrm{NL} < 34.4 exp({3.3, n_{f_mathrm{NL}}})$ at 95% CL. These results incorporate uncertainties in the cosmological parameters, redshift distributions, shot noise, and the bias prescription used to relate the quasar clustering to the underlying dark matter. These are the strongest constraints obtained to date on PNG using a single population of large-scale structure tracers, and are already at the level of pre-{it Planck} constraints from the cosmic microwave background. A conservative forecast for a {it Large Synoptic Survey Telescope}-like survey incorporating mode projection yields $sigma(f_mathrm{NL}) sim 5$ -- competitive with the {it Planck} result -- highlighting the power of upcoming large scale structure surveys to probe the initial conditions of the universe.
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