MULTIPOLE FORMULAE FOR GRAVITATIONAL LENSING SHEAR AND FLEXION
- Department of Physics and Astronomy, University of Pennsylvania, 209 S. 33rd St., Philadelphia, PA 19104 (United States)
The gravitational lensing equations for convergence, potential, shear, and flexion are simple in polar coordinates and separate under a multipole expansion once the shear and flexion spinors are rotated into a 'tangential' basis. We use this to investigate whether the useful monopole aperture-mass shear formulae generalize to all multipoles and to flexions. We re-derive the result of Schneider and Bartelmann that the shear multipole m at radius R is completely determined by the mass multipole at R, plus specific moments Q '('m') {sub in} and Q '('m') {sub out} of the mass multipoles internal and external, respectively, to R. The m {>=} 0 multipoles are independent of Q {sub out}. But in contrast to the monopole, the m < 0 multipoles are independent of Q {sub in}. These internal and external mass moments can be determined by shear (and/or flexion) data on the complementary portion of the plane, which has practical implications for lens modeling. We find that the ease of E/B separation in the monopole aperture moments does not generalize to m {ne} 0: the internal monopole moment is the only nonlocal E/B discriminant available from lensing observations. We have also not found practical local E/B discriminants beyond the monopole, though they could exist. We show also that the use of weak-lensing data to constrain a constant shear term near a strong-lensing system is impractical without strong prior constraints on the neighboring mass distribution.
- OSTI ID:
- 21279460
- Journal Information:
- Astrophysical Journal, Vol. 693, Issue 2; Other Information: DOI: 10.1088/0004-637X/693/2/1508; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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