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Intrinsic and extrinsic galaxy alignment

Catelan, Paolo and Kamionkowski, Marc and Blandford, Roger D. (2001) Intrinsic and extrinsic galaxy alignment. Monthly Notices of the Royal Astronomical Society, 320 (1). L7-L13. ISSN 0035-8711.

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We show with analytic models that the assumption of uncorrelated intrinsic ellipticities of target sources that is usually made in searches for weak gravitational lensing arising from large-scale mass inhomogeneities (‘field lensing’) is unwarranted. If the orientation of the galaxy image is determined either by the angular momentum or by the shape of the halo in which it forms, then the image should be aligned preferentially with the component of the tidal gravitational field perpendicular to the line of sight. Long-range correlations in the tidal field will thus lead to long-range ellipticity–ellipticity correlations that mimic the shear correlations arising from weak gravitational lensing. We calculate the ellipticity–ellipticity correlation expected if halo shapes determine the observed galaxy shape, and we discuss uncertainties (which are still considerable) in the predicted amplitude of this correlation. The ellipticity–ellipticity correlation induced by angular momenta should be smaller. We consider several methods for discriminating between the weak-lensing (extrinsic) and intrinsic correlations, including the use of redshift information. An ellipticity–tidal-field correlation also implies the existence of an alignment of images of galaxies near clusters. Although the intrinsic alignment may complicate the interpretation of field-lensing results, it is inherently interesting as it may shed light on galaxy formation as well as on structure formation.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Kamionkowski, Marc0000-0001-7018-2055
Blandford, Roger D.0000-0002-1854-5506
Additional Information:© 2001 RAS. Accepted 2000 October 11. Received 2000 October 2; in original form 2000 May 31. We thank D. Bacon, R. Croft, R. Ellis, A. Heavens, M. Metzger, C. Metzler, A. Refregier, M. Santos and M. White for discussions, and we thank especially U.-L. Pen and M. Zaldarriaga for identifying an error in an earlier draft. This work was supported in part by NSF AST-9900866, AST-0096023, NASA NAG5-8506, and DoE DE-FG03-92-ER40701.
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG03-92-ER40701
Subject Keywords:gravitational lensing, cosmology: theory, large-scale structure of Universe
Issue or Number:1
Record Number:CaltechAUTHORS:20170409-072654766
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Official Citation:Paolo Catelan, Marc Kamionkowski, Roger D. Blandford; Intrinsic and extrinsic galaxy alignment, Monthly Notices of the Royal Astronomical Society, Volume 320, Issue 1, 1 January 2001, Pages L7–L13,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:76435
Deposited By: 1Science Import
Deposited On:03 Apr 2018 20:48
Last Modified:03 Oct 2019 17:01

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