Intrinsic galaxy alignments from the 2SLAQ and SDSS surveys: luminosity and redshift scalings and implications for weak lensing surveys

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dc.creatorHirata, Christopher M.
dc.creatorMandelbaum, Rachel
dc.creatorIshak, Mustapha
dc.creatorSeljak, Uros
dc.creatorNichol, Robert
dc.creatorPimbblet, Kevin A.
dc.creatorRoss, Nicholas P.
dc.creatorWake, David
dc.date2007-01-24
dc.date2007-10-28
dc.date.accessioned2026-07-07T12:36:35Z
dc.date.available2026-07-07T12:36:35Z
dc.descriptionCorrelations 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 0.15<z<0.35, split by redshift and luminosity; 7758 LRGs from the 2SLAQ Survey at 0.4<z<0.8; and a variety of other SDSS samples from previous, related work. We find >3sigma 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)
dc.descriptionMatches MNRAS accepted version. Extended/updated data tables and expanded comparison to theory
dc.identifierhttps://arxiv.org/abs/astro-ph/0701671
dc.identifierhttp://arxiv.org/abs/astro-ph/0701671
dc.identifierMon.Not.Roy.Astron.Soc.381:1197-1218,2007
dc.identifierdoi:10.1111/j.1365-2966.2007.12312.x
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/218144
dc.subjectAstrophysics
dc.titleIntrinsic galaxy alignments from the 2SLAQ and SDSS surveys: luminosity and redshift scalings and implications for weak lensing surveys
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