Simulations for 21 cm radiation lensing at EoR redshifts

Abstract

We introduce simulations aimed at assessing how well weak gravitational lensing of 21cm radiation from the Epoch of Reionization (z ∼ 8) can be measured by an SKA-like radio telescope. A simulation pipeline has been implemented to study the performance of lensing reconstruction techniques. We show how well the lensing signal can be reconstructed using the three-dimensional quadratic lensing estimator in Fourier space assuming different survey strategies. The numerical code introduced in this work is capable of dealing with issues that can not be treated analytically such as the discreteness of visibility measurements and the inclusion of a realistic model for the antennae distribution. This paves the way for future numerical studies implementing more realistic reionization models, foreground subtraction schemes, and testing the performance of lensing estimators that take into account the non Gaussian distribution of HI after reionization. If multiple frequency channels covering z ∼ 7 − 11.6 are combined, Phase 1 of SKA-Low should be able to obtain good quality images of the lensing potential with a total resolution of ∼ 1.6 arcmin. The SKA-Low Phase 2 should be capable of providing images with high-fidelity even using data from z ∼ 7.7−8.3. We perform tests aimed at evaluating the numerical implementation of the mapping reconstruction. We also discuss the possibility of measuring an accurate lensing power spectrum. Combining data from z ∼ 7 − 11.6 using the SKA2-Low telescope model, we find constraints comparable to sample variance in the range L < 1000, even for survey areas as small as 25 deg 2 .

Lensing reconstruction from line intensity maps: the impact of gravitational nonlinearity

“…Note that similar expressions in the literature (e.g. [19,30]) often have an extra factor of 2 in the denominator of the integrand of Eq. (2.15).…”

“…We use the values for phase 1 of SKA-Low, also from Ref. [30]: A e = 925 m 2 is the effective receiving area of a single station, ν c = 110 MHz is the "critical frequency" above which the effective receiving area receives a multiplicative correction of (ν c /ν) 2 , N pol = 2 is the number of polarizations per receiver, B = 5 MHz is the observing bandwidth, and t 0 = 2000 hrs is the total observing time. The system temperature T sys is the fundamental source of thermal noise in an antenna, and has contributions from the instrumental receiver temperature, set to 40 K, and galactic synchrotron radiation, which can be approximated as (4.6)…”

“…Other estimators have also been discussed, including configuration-space correlation-function-based estimators [22,23] similar to those for the CMB [24,25], mixed configuration-Fourier space estimators [22], and estimators for the lensing convergence and shear instead of the deflection angle [26,27]. Fourier-space estimators have been further investigated, in the presence of a Poisson component of the source field power spectrum [28,29] and in simulations [30]. An alternative method for calculating the effect of lensing on 21cm observations, involving a Wilsonian cutoff-based approach that leads to a system of differential equations, was investigated in Ref.…”

Fundamental physics with the Square Kilometre Array

“…Increasing the survey area would allow access to large angular scales, where the signal-to-noise is the greatest. This measurement would be significantly improved with the larger sensitivity of SKA2 (Romeo et al 2018). For redshifts after reionisation, the power spectrum of weak lensing should be better measured using SKA-Mid and the 21-cm intensity mapping (IM) approach discussed above, but covering a much wider sky area (Pourtsidou & Metcalf 2014).…”

Full-sky lensing reconstruction of 21 cm intensity maps

“…LIM has lately been considered as a promising new probe of the lensing potential. LIM lensing has mostly been considered in terms of the 3D Fourier-space quadratic estimator derived in Zahn & Zaldarriaga (2006) while numerous other estimators have also been considered (Mandel & Zaldarriaga 2006;Metcalf & White 2007;Lu & Pen 2008;Metcalf & White 2009;Lu et al 2010;Pourtsidou & Metcalf 2014, 2015Romeo et al 2018) LIM has significant advantages over traditional lensing tracers. For one, unlike CMB fluctuations, 21-cm fluctuations do not experience Silk damping on small scales (Hu & White 1997); they are limited instead by the Jeans length of the gas which occurs at much smaller scales (Loeb & Zaldarriaga 2004), providing more power to sample the lens field.…”