TITLE:
Intrinsic alignment-lensing interference as a contaminant of cosmic shear
AUTHOR(S):
Christopher M. Hirata and Uros Seljak (Princeton Univ.)
DATE:
2004 Jun 10 (arXiv, v1, posted); 2004 Jun 15 (Phys. Rev. D, submitted);
2004 Aug 20 (revised); 2004 Aug 24 (Phys. Rev. D, accepted);
2004 Sep 14 (arXiv, v2, posted); 2004 Sep 21 (Phys. Rev. D, published).
AVAILABILITY:
arXiv
astro-ph/0406275 (free);
PROLA (requires subscription).
PUBLICATION INFORMATION:
Physical Review D, 70, 063526 (2004), 11 pages.
ABSTRACT:
Cosmic shear surveys have great promise as tools for precision cosmology,
but can be subject to systematic errors including intrinsic
ellipticity correlations of the source galaxies. The intrinsic alignments
are believed to be small for deep surveys, but this is based on intrinsic
and lensing distortions being uncorrelated. Here we show that the
gravitational lensing shear and intrinsic shear need not be independent:
correlations between the tidal field and the intrinsic shear cause the
intrinsic shear of nearby galaxies to be correlated with the gravitational
shear acting on more distant galaxies. We estimate the magnitude of this
effect for two simple intrinsic alignment models: one in which the galaxy
ellipticity is linearly related to the tidal field, and one in which it is
quadratic in the tidal field as suggested by tidal torque theory. The
first model predicts a gravitational-intrinsic (GI) correlation that can
be much greater than the intrinsic-intrinsic (II) correlation for broad
redshift distributions, and that remains when galaxies pairs at similar
redshifts are rejected. The second model, in its simplest form, predicts
no gravitational-intrinsic correlation. In the first model and assuming a
normalization consistent with recently claimed detections of intrinsic
correlations we find that the GI correlation term can exceed the usual
II term by >1 order of magnitude and the intrinsic correlation
induced B-mode by 2 orders of magnitude. These interference effects
can suppress the lensing power spectrum for a single broad redshift
bin by of order ~10% at zs=1 and ~30% at zs=0.5. We
conclude that, depending on the intrinsic alignment model, the
GI correlation may be the dominant contaminant of the lensing signal and
can even affect cross-spectra between widely separated bins. We describe
two ways to constrain this effect, one based on density-shear correlations
and one based on scaling of the cross-correlation tomography signal with
redshift.
ADS BIBLIOGRAPHIC CODE:
2004PhRvD..70f3526H
COMMENTS: