Dark energy constraints from cosmic shear power spectra: impact of intrinsic alignments on photometric redshift requirements

By Sarah Bridle, L. King. 2007

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Cosmic shear constrains cosmology by exploiting the apparent alignments of pairs of galaxies due to gravitational lensing by intervening mass clumps. However, galaxies may become (intrinsically) aligned with each other, and with nearby mass clumps, during their formation. This effect needs to be disentangled from the cosmic shear signal to place constraints on cosmology. We use the linear intrinsic alignment model as a base and compare it to an alternative model and data. If intrinsic alignments are ignored then the dark energy equation of state is biased by ∼50%. We examine how the number of tomographic redshift bins affects uncertainties on cosmological parameters and find that when intrinsic alignments are included two or more times as many bins are required to obtain 80% of the available information. We investigate how the degradation in the dark energy figure of merit depends on the photometric redshift scatter. Previous studies have shown that lensing does not place stringent requirements on the photometric redshift uncertainty, so long as the uncertainty is well known. However, if intrinsic alignments are included the requirements become a factor of three tighter. These results are quite insensitive to the fraction of catastrophic outliers, assuming that this fraction is well known. We show the effect of uncertainties in photometric redshift bias and scatter. Finally, we quantify how priors on the intrinsic alignment model would improve dark energy constraints.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/7fd45504fa08d97ab352acb43056e541950c81bf

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Citations in the corpus

KiDS-450: The tomographic weak lensing power spectrum and constraints on cosmological parameters (2017, neutral): “…these effects as in Hildebrandt et al. (2017) and employ the non-linear modification of the tidal alignment model of IAs (Hirata & Seljak 2004; Bridle & King 2007; Joachimi et al. 2011), so that we can write CIIμν( ) = ∫ χH 0 dχ nμ(χ )nν(χ )F 2(χ ) f 2K(χ ) Pδ ( k = + 0.5 fK(χ ) ; χ )…”
Results of the GREAT08 Challenge?: an image analysis competition for cosmological lensing: Results o (2009, background): “…alignment signal (ii) can be removed if (i) can be solved perfectly (Takada & White 2004; Joachimi & Schneider 2008) and otherwise the two are closely linked (Heymans & Heavens 2003; King & Schneider 2003; King 2005; Bridle & King 2007; Zhang 2008; Bernstein 2009; Joachimi & Schneider 2009).”
Observational probes of cosmic acceleration (2012, background): “These errors, and the steps to remove them, are not independent — for example, marginalizing out the intrinsic alignment effects can amplify systematic errors in photometric redshifts (Bridle and King, 2007).”
KiDS+GAMA : cosmology constraints from a joint analysis of cosmic shear, galaxy-galaxy lensing, and angular clustering (2017, background): “…which is assumed to follow the non-linear modification of the linear alignment model (Catelan, Kamionkowski & Blandford 2001; Hirata & Seljak 2004; Bridle & King 2007; Hirata & Seljak 2010): PδI(k, z) = −AIAC1ρcrit m D(z) Pδ(k, z), (21) with Pδ(k, z) the full non-linear matter power spectrum,…”
Cosmic Discordance: Are Planck CMB and CFHTLenS weak lensing measurements out of tune? (2014, methodology): “We follow HE13 by using the non-linear linear alignment model (henceforth NLA model, Bridle & King (2007)) to account for intrinsic alignments.”
Galaxy Alignments: Observations and Impact on Cosmology (2015, methodology): “Mandelbaum et al. (2011) fit two simple models to their intrinsic alignment measurements: a power-law in transverse separation and the non-linear alignment model with an additional free power-law dependence on redshift (Bridle & King 2007).”
Weak Gravitational Lensing (2012, background): “The parameters of the model can thus be varied and marginalized over to constrain cosmological parameters [13, 10, 39].”
Cosmological constraints from cosmic shear two-point correlation functions with HSC survey first-year data (2019, methodology): “We employ the standard theoretical model for these terms, namely, the nonlinear modification of the tidal alignment model (Hirata & Seljak 2004; Bridle & King 2007; Joachimi et al. 2011).”
Galaxy Alignments: An Overview (2015, methodology): “The first study of intrinsic alignments that had many galaxy pairs on the scales used for cosmological weak lensing analysis was that of Brown et al. (2002). They used digitized photographic data (which is subject to a number of technical difficulties in shape measurement, see Section 1) from the Su”
The WiggleZ Dark Energy Survey: Direct constraints on blue galaxy intrinsic alignments at intermediate redshifts (2009, methodology): “…the contributions to the lensing power spectra.2 This model is not expected to be an accurate description of alignments on non-linear scales, and Bridle & King (2007) were inspired by H07 to insert the non-linear matter power spectrum into the model in place of the linear matter power spectrum.”
The Intrinsic Alignment of Galaxies and its Impact on Weak Gravitational Lensing in an Era of Precision Cosmology (2014, methodology): “A more general approach is that of Bridle and King (2007), where a parameterized set of models is constructed which vary from a base physical model, in this case the nonlinear alignment model, through a reasonable set of the parameter space.”
Constraints on intrinsic alignment contamination of weak lensing surveys using the MegaZ-LRG sample (2010, methodology): “Our default normalisation of the growth factor is in line with Bridle & King (2007) whose value forC1 we have adopted.”
CFHTLenS revisited: assessing concordance with Planck including astrophysical systematics (2016, background): “Following Bridle & King (2007) in using the non-linear matter power spectrum within the linear theory of Hirata & Seljak (2004), we express the II term: C ij II ( ) = ∫ χH 0 dχ ni(χ )nj (χ )Fi(χ )Fj (χ ) [fK (χ )]2 Pδδ ( + 1/2 fK (χ ) , χ ) , (5) and the GI term: C ij GI( ) = ∫ χH 0 dχ qi(χ )nj (χ…”