Christopher Hirata's Publication List

TITLE: Intrinsic galaxy alignments from the 2SLAQ and SDSS surveys: luminosity and redshift scalings and implications for weak lensing surveys
AUTHOR(S): Christopher M. Hirata, Rachel Mandelbaum (IAS); Mustapha Ishak (UT Dallas); Uros Seljak (Zurich); Robert Nichol (Portsmouth); Kevin Pimbblet (Queensland); Nicholas P. Ross and David Wake (Durham).
DATE: 2007 Jan 24 (arXiv, v1, posted); 2007 Jan 27 (MNRAS, submitted); 2007 Jul 30 (revised); 2007 Aug 01 (MNRAS, accepted); 2007 Sep 26 (MNRAS, published); 2007 Oct 28 (arXiv, v2, posted).
AVAILABILITY: arXiv astro-ph/0701671 (free); Blackwell Synergy (requires subscription).
PUBLICATION INFORMATION: Mon. Not. R. Astron. Soc. 381, 1197--1218 (2007).
ABSTRACT: Correlations between intrinsic shear and the density field on large scales, a potentially important contaminant for cosmic shear surveys, have been robustly detected at low redshifts with bright galaxies in SDSS data. Here we present a more detailed characterization of this effect, which can cause anti-correlations between gravitational lensing shear and intrinsic ellipticity (GI correlations). This measurement uses 36278 Luminous Red Galaxies (LRGs) from the SDSS spectroscopic sample with 0.153sigma detections of the effect for all galaxy subsamples within the SDSS LRG sample; for the 2SLAQ sample, we find a 2sigma detection for a bright subsample, and no detection for a fainter subsample. Fitting formulae are provided for the scaling of the GI correlations with luminosity, transverse separation, and redshift. We estimate contamination in the measurement of sigma_8 for future cosmic shear surveys on the basis of the fitted dependence of GI correlations on galaxy properties. We find contamination to the power spectrum ranging from -1.5 (optimistic) to -33 per cent (pessimistic) for a toy cosmic shear survey using all galaxies to a depth of R=24 using scales l~500. This corresponds to a bias in sigma_8 of Delta sigma_8=-0.004 (optimistic), -0.02 (central), or -0.10 (pessimistic). We provide a prescription for inclusion of this error in cosmological parameter estimation codes. The principal uncertainty is in the treatment of the L<=L* blue galaxies. Characterization of the tidal alignments of these galaxies, especially at redshifts relevant for cosmic shear, should be a high priority for the cosmic shear community. (Abridged)
ADS BIBLIOGRAPHIC CODE: 2007MNRAS.381.1197H
COMMENTS: This is a follow-up to our earlier paper looking for the effect at low redshift.

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