Multi-wavelength spectroscopic probes: biases from neglecting light-cone effects

Abstract

Next-generation cosmological surveys will observe larger cosmic volumes than ever before, enabling us to access information on the primordial Universe, as well as on relativistic effects. In a companion paper, we applied a Fisher analysis to forecast the expected precision on f NL and the detectability of the lensing magnification and Doppler contributions to the power spectrum. Here we assess the bias on the best-fit values of f NL and other parameters, from neglecting these light-cone effects. We consider forthcoming 21cm intensity mapping surveys (SKAO) and optical galaxy surveys (DESI and Euclid), both individually and combined together. We conclude that lensing magnification at higher redshifts must be included in the modelling of spectroscopic surveys. If lensing is neglected in the analysis, this produces a bias of more than 1σ -not only on f NL , but also on the standard cosmological parameters.

Anti-symmetric clustering signals in the observed power spectrum

“…Such relativistic effects only become important on the largest scales and for most purposes can be safely neglected in standard cosmological parameter estimation from single tracer clustering [16]. However, for combinations of multiple tracers, this is no longer true [17].…”

Constraining primordial non-Gaussianity by combining next-generation galaxy and 21 cm intensity mapping surveys

“…where the amplitude b A0 is a free parameter. We highlight the point that a multi-tracer approach reduces the impact of this assumption on σ(f NL ) [35].…”

“…• A theoretical systematic arising from the neglect of lensing magnification and other relativistic lightcone effects on the power spectrum, which can bias the best-fit f NL [22][23][24][25][26][27][28][29][30][31][32][33][34][35]. Although the bias on best-fit can be large, the error σ(f NL ) is not significantly affected and we therefore omit these lightcone effects.…”

On cosmological bias due to the magnification of shear and position samples in modern weak lensing analyses

“…It is common for the analysis of modern weak lensing surveys to analyse a "3x2pt" data vector containing the cosmic shear, galaxy-galaxy lensing and galaxy clustering, each a 2-point correlation in either Fourier/Harmonic space or configuration space. The effect of magnification in the position signal (termed "magnification bias") causes additional correlations in the clustering and galaxy-galaxy lensing part of the 3x2pt data vectors, and the impacts of such an effect on cosmological parameter estimation is now well studied (Duncan et al 2014;Raccanelli et al 2016;Cardona et al 2016;Lorenz et al 2018;Villa et al 2018;Thiele et al 2020;Tanidis et al 2020;Viljoen et al 2021). These studies show a consistent picture, that indicates that this magnification bias may provide cosmological information on clustering studies, but does not add valuable extra cosmological information E-mail: christopher.duncan@physics.ox.ac.uk when combined with weak lensing shear measurements.…”