# Galaxy-Galaxy Lensing by Non-Spherical Haloes I:Theoretical Considerations - Astrophysics > Cosmology and Nongalactic Astrophysics

Galaxy-Galaxy Lensing by Non-Spherical Haloes I:Theoretical Considerations - Astrophysics > Cosmology and Nongalactic Astrophysics - Download this document for free, or read online. Document in PDF available to download.

Abstract: We use Monte Carlo simulations to investigate the theory of galaxy-galaxylensing by non-spherical dark matter haloes. The simulations include a carefulaccounting of the effects of multiple deflections. In a typical data set wherethe mean tangential shear of sources with redshifts zs ~ 0.6 is measured withrespect to the observed symmetry axes of foreground galaxies with redshifts zl~ 0.3, the signature of anisotropic galaxy-galaxy lensing differs substantiallyfrom the expectation that one would have in the absence of multipledeflections. The observed ratio of the mean tangential shears, g+-g-, isstrongly suppressed compared to the function that one would measure if theintrinsic symmetry axes of the foreground galaxies were known. Depending uponthe characteristic masses of the lenses, the observed ratio of the meantangential shears may be consistent with an isotropic signal despite the factthat the lenses are non-spherical, or it may even be reversed from theexpected signal i.e., the mean tangential shear for sources close to theobserved minor axes of the lenses may exceed the mean tangential shear forsources close to the observed major axes of the lenses. These effects arecaused primarily by the fact that the lens galaxies have, themselves, beenlensed and therefore the observed symmetry axes of the lenses differ from theirintrinsic symmetry axes. The effects of lensing of the foreground galaxies onthe observed function g+-g- cannot be eliminated by the rejection of foregroundgalaxies with small image ellipticities, nor by focusing the analysis onsources that are located very close to the observed symmetry axes of theforeground galaxies. We conclude that any attempt to use a measurement of g+-g-to constrain the shapes of dark matter galaxy haloes must include Monte Carlosimulations that take multiple deflections properly into account.

Author: ** Paul J. Howell, Tereasa G. Brainerd**

Source: https://arxiv.org/