Constraining primordial non-Gaussianity using two galaxy surveys and CMB lensing

Abstract

Next-generation galaxy surveys will be able to measure perturbations on scales beyond the equality scale. On these ultra-large scales, primordial non-Gaussianity leaves signatures that can shed light on the mechanism by which perturbations in the early Universe are generated. We perform a forecast analysis for constraining local type non-Gaussianity and its two-parameter extension with a simple scale-dependence. We combine different clustering measurements from future galaxy surveys -a 21cm intensity mapping survey and two photometric galaxy surveys -via the multi-tracer approach. Furthermore we then include CMB lensing from a CMB Stage 4 experiment in the multi-tracer, which can improve the constraints on bias parameters. We forecast σ( f NL ) 0.9 (1.4) by combining SKA1, a Euclid-like (LSST-like) survey, and CMB-S4 lensing. With CMB lensing, the precision on f NL improves by up to a factor of 2, showing that a joint analysis is important. In the case with running of f NL , our results show that the combination of upcoming cosmological surveys could achieve σ(n NL ) 0.12 (0.22) on the running index.

Optimal filters for the moving lens effect

“…We use lensed C ΘΘ , approximate the kSZ contribution as a constant 3 µK 2 in ( + 1)/(2π) 2 C ΘΘ and assume perfect removal of foregrounds such as the cosmic infrared background and tSZ from the CMB. Note that individual halo masses are expected to be measured imperfectly, with around 40 percent error in ln M , from combinations of lensing and SZ measurements and redshift measurements are subject to photo-z errors [9,21,22]. We discuss these in Section VI, before forecasting on the transverse velocity amplitude reconstruction fidelity of the upcoming surveys in cross correlations of CMB and galaxy measurements.…”

“…In particular, there is evidence that the measurement of small-scale secondary anisotropies that are imprinted on the CMB by cosmological structures between our telescopes and the surface of last scattering will provide strong constrains on a multitude of cosmological signatures (see e.g. [4][5][6][7][8][9][10]). The statistics of these secondaries and their cross-correlations with large-scale structure (LSS) surveys carry information about cosmological fluctuations on large scales.…”

Predictions for local PNG bias in the galaxy power spectrum and bispectrum and the consequences for $f_{\rm NL}$ constraints

“…In this way, the contribution scales as ∝ (b 1 − 1) f nl /k 2 , and since b 1 can in principle be constrained using the smaller-scale part of the power spectrum (where f nl contributes weakly), it then becomes possible to constrain f nl . The universality relation is adopted by almost all existing galaxy data constraints on f nl [16,[18][19][20][21][22][23][24][25] (the current tightest bound is f nl = −12 ± 21 (1σ) [25]), as well as in forecast studies [7,[26][27][28][29][30][31][32][33][34][35][36] for next-generation surveys. Despite its widespread adoption, there is however no reason to expect the universality relation to hold for real-life galaxy samples, and in fact, studies using N -body simulations have been indicating this to be the case already.…”

Cosmological parameter forecasts by a joint 2D tomographic approach to CMB and galaxy clustering

“…Current estimates for this SNR is around ∼20 (for Planck and NVSS [21]), but a sensible improvement is expected in the perspective of future CMB experiments, which will improve the measurement of CMB lensing. It has been studied how this cross-correlation will contribute to the measurements of the amplitude of matter fluctuations, neutrino mass [25,26], primordial non-Gaussianities [26][27][28], and galaxy bias. The cross-correlations of CMB lensing with galaxies and galaxy shear is also used in lensing ratio estimators, which can mitigate the uncertainties of the galaxy bias [29][30][31][32].…”