Weak-lensing observables in relativistic N-body simulations

Abstract

<jats:title>Abstract</jats:title> <jats:p>We present a numerical weak-lensing analysis that is fully relativistic and non-perturbative for the scalar part of the gravitational potential and first-order in the vector part, frame dragging. Integrating the photon geodesics backwards from the observer to the emitters, we solve the Sachs optical equations and study in detail the weak-lensing convergence, ellipticity and rotation. For the first time, we apply such an analysis to a high-resolution relativistic N-body simulation, which consistently includes the leading-order corrections due to general relativity on both large and small scales. These are related to the question of gauge choice and to post-Newtonian corrections, respectively. We present the angular power spectra and one-point probability distribution functions for the weak-lensing variables, which we find are broadly in agreement with comparable Newtonian simulations. Our geometric approach, however, is more robust and flexible, and can therefore be applied consistently to non-standard cosmologies and modified theories of gravity.</jats:p>

Clustering dark energy imprints on cosmological observables of the gravitational field

“…In this work, we use a fast pixel-based method to solve the integrals of equations ( 13), (24), and (29) in the Born approximation, given that post-Born corrections typically affect the angular power spectra only at very high multipoles. A comparison of this approach with 'exact' ray tracing of the deformed geodesics is presented in Lepori et al (2020) for the case of the weak-lensing convergence (see also Pratten & Lewis 2016) and justifies the use of the Born approximation for the multipoles discussed here. Note, however, that post-Born corrections can play an important role in higher order correlation functions like the angular bispectrum.…”

“…In Adamek et al (2019), some of us have implemented a raytracing method to analyse relativistic N-body simulations performed with the code GEVOLUTION. In this method, one solves the optical equations in the scalar sector of gravity without any approximation and additionally keeps track of the frame dragging to first order. Weak-lensing convergence and shear obtained with this numerical method were studied in more detail in Lepori et al (2020). While other approaches often try to reconstruct the signal from the mass distribution, our method works with the metric perturbations directly and is therefore more robust once we consider DE/MG like in this work.…”

“…N-body simulation data agree better compared to the lower redshift results, as the scale where the finite resolution of the simulation affects the result is shifted to higher multipoles; see Appendix A (cf. also appendix C of Lepori et al 2020). Moreover, the relative difference between the angular power spectra is less substantial compared to lower redshift result that comes from the fact that dark energy starts to dominate at lower redshift and integrating to higher redshifts therefore effectively dilutes the signal.…”

“…The relation between a non-perturbative geometrical description and these first-order quantities is discussed in detail in Lepori et al (2020).…”

Observing relativistic features in large-scale structure surveys – I. Multipoles of the power spectrum

“…We apply a ray tracing algorithm to our simulation as a postprocessing tool. The algorithm was previously described in Lepori et al (2020),butwegiveabriefreviewofithere.…”