Open AccessMeasuring the three‐dimensional shear from simulation data, with applications to weak gravitational lensing
Author(s) -
Couchman H. M. P.,
Barber Andrew J.,
Thomas Peter A.
Publication year - 1999
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1999.02714.x
Subject(s) - physics , weak gravitational lensing , gravitational lens , convolution (computer science) , algorithm , fourier transform , planar , gravitation , computational physics , mathematical analysis , classical mechanics , galaxy , astrophysics , computer science , redshift , mathematics , computer graphics (images) , quantum mechanics , machine learning , artificial neural network
We have developed a new three‐dimensional algorithm, based on the standard P 3 M method, for computing deflections resulting from weak gravitational lensing. We compare the results of this method with those of the two‐dimensional planar approach, and rigorously outline the conditions under which the two approaches are equivalent. Our new algorithm uses a Fast Fourier Transform convolution method for speed, and has a variable softening feature to provide a realistic interpretation of the large‐scale structure in a simulation. The output values of the code are compared with those from the Ewald summation method, which we describe and develop in detail. With an optimal choice of the high‐frequency filtering in the Fourier convolution, the maximum errors, when using only a single particle, are about 7 per cent, with an rms error less than 2 per cent. For ensembles of particles, used in typical N ‐body simulations, the rms errors are typically 0.3 per cent. We describe how the output from the algorithm can be used to generate distributions of magnification, source ellipticity, shear and convergence for large‐scale structure.