Journal Article

Galaxy–galaxy lensing by non-spherical haloes – I. Theoretical considerations

Paul J. Howell and Tereasa G. Brainerd

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 407, issue 2, pages 891-909
Published in print September 2010 | ISSN: 0035-8711
Published online September 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.16979.x
Galaxy–galaxy lensing by non-spherical haloes – I. Theoretical considerations

More Like This

Show all results sharing this subject:

  • Astronomy and Astrophysics

GO

Show Summary Details

Preview

We use a series of Monte Carlo simulations to investigate the theory of galaxy–galaxy lensing by non-spherical dark matter haloes. The simulations include a careful accounting of the effects of multiple deflections on the galaxy–galaxy lensing signal. In a typical observational data set where the mean tangential shear of sources with redshifts zs≃ 0.6 is measured with respect to the observed symmetry axes of foreground galaxies with redshifts zl≃ 0.3, we find that the signature of anisotropic galaxy–galaxy lensing differs substantially from the simple expectation that one would have in the absence of multiple deflections. In general, the observed ratio of the mean tangential shears, γ+(θ)/γ(θ), is strongly suppressed compared to the function that one would measure if the intrinsic symmetry axes of the foreground galaxies were known. Depending upon the characteristic masses of the lenses, the observed ratio of the mean tangential shears may be consistent with an isotropic signal (despite the fact that the lenses are non-spherical), or it may even be reversed from the expected signal (i.e. the mean tangential shear for sources close to the observed minor axes of the lenses may exceed the mean tangential shear for sources close to the observed major axes of the lenses). These effects are caused primarily by the fact that the images of the lens galaxies have, themselves, been lensed and therefore the observed symmetry axes of the lens galaxies differ from their intrinsic symmetry axes. We show that the effects of lensing of the foreground galaxies on the observed function γ+(θ)/γ(θ) cannot be eliminated simply by the rejection of foreground galaxies with very small image ellipticities nor by simply focusing the analysis on sources that are located very close to the observed symmetry axes of the foreground galaxies. We conclude that any attempt to use a measurement of γ+(θ)/γ(θ) to constrain the shapes of dark matter galaxy haloes must include Monte Carlo simulations that take multiple deflections properly into account.

Keywords: gravitational lensing; galaxies: haloes; dark matter

Journal Article.  11967 words.  Illustrated.

Subjects: Astronomy and Astrophysics

Full text: subscription required

How to subscribe Recommend to my Librarian

Users without a subscription are not able to see the full content. Please, subscribe or login to access all content.