Future constraints on angle-dependent non-Gaussianity from large radio surveys

Abstract

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 angle dependence between the three wavevectors that is characterized by Legendre polynomials PL and expansion coefficients cL. We provide forecasts for measurements of galaxy power spectrum, finding that Large-Scale Structure (LSS) data could allow measurements of primordial non-Gaussianity that would be competitive with, or improve 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 fNL loc≈1(0.5) for the local shape, fNL of O(10)(O(1)) for the orthogonal, equilateral and folded shapes, and cL=1≈80(2), cL=2≈400(10) for angle-dependent non-Gaussianity showing that only futuristic galaxy surveys will be able to set strong constraints on these models. Nevertheless, 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 σ(cL=1)=10, which can be considered as a typical (lower) value predicted by some (inflationary) models. © 201

Towards a measurement of the spectral runnings

“…Moreover, multi-tracer (MT) analyses [98,99], where one can divide the galaxy catalog into subsamples of different populations, can potentially improve the constraints from galaxy surveys by a factor of a few, depending on the assumptions on the number of distinguishable populations and their bias (for some first analyses using the MT technique, see Refs. [87,[100][101][102][103][104] We show the confidence ellipses for a DESI-like survey, as well as for a SKA-like survey, in Fig. 3, where we also include the information from Planck.…”

“…, where σ v is the velocity dispersion and is modeled as in [87]. A real data analysis will need to take into account a variety of additional corrections, such as wide-angle effects [88][89][90], and cosmic magnification [91,92]; however none of these effects should be degenerate with modifications of the power spectrum spectral index or its runnings, so we will not include a detailed modeling of them.…”

The gravitational and lensing-ISW bispectrum of 21 cm radiation

“…They predict that a cosmic variance limited experiment would be able to measure fNL down to σ f NL ∼ 0.03, and thus able to constrain single-field slow-roll inflation (Maldacena 2003;Acquaviva et al 2003). Observations of PNG at lower redshifts rely on the scale dependence of the halo bias and can achieve competitive constraints for the primordial non-Gaussianity parameter D'Aloisio et al 2013;Li & Ma 2017;Raccanelli et al 2017;Karagiannis et al 2018). The prospects of constraining PNG with the cosmic 21cm signal are thus promising.…”

Constraints on primordial non-Gaussianity from future Hi intensity mapping experiments

“…More accurate analytical expressions for the scaledependent bias have been studied [17][18][19][20][21][22]. A widely used expression is derived by Matarrese and Verde [17],…”

“…Current measurements of the temperature and polarization of CMB from the Planck satellite provide state-of-the-art constraints on local, equilateral and orthogonal types of PNG [15] as f Besides the constraints from CMB, there have been many efforts to measure f NL through large-scale structure surveys. This is because the PNG induces a scale-dependent bias of the galaxy with respect to the underlying dark matter distribution tracer [16][17][18][19][20][21][22]. Reference [19] used spectroscopic and photometric luminous red galaxy samples and quasar samples * Electronic address: lixiating@gmail.com † Electronic address: ma@ukzn.ac.za from the SDSS survey to obtain the limit for local-type PNG as −31(−96) < f local NL < +70(+96) at 95% (99.7%) C.L., which was comparable to the measurements at the time from the Wilkinson Microwave Anisotropy Probe (WMAP) five-year results.…”