Self-Calibration of Gravitational Shear-Galaxy Intrinsic Ellipticity Correlation in Weak Lensing Surveys

Abstract

The galaxy intrinsic alignment is a severe challenge to precision cosmic shear measurement. We propose to self-calibrate the induced gravitational shear-galaxy intrinsic ellipticity correlation (the GI correlation, Hirata & Seljak 2004) in weak lensing surveys with photometric redshift measurement.(1) We propose a method to extract the intrinsic ellipticity-galaxy density cross correlation (I-g) from the galaxy ellipticity-density measurement in the same redshift bin.(2) We also find a generic scaling relation to convert the extracted I-g correlation to the demanded GI correlation. We perform concept study under simplified conditions and demonstrate its capability to significantly reduce the GI contamination. We discuss the impact of various complexities on the two key ingredients of the self-calibration technique, namely the method to extract the I-g correlation and the scaling relation between the I-g and the GI correlation. We expect none of them is likely able to completely invalidate the proposed self-calibration technique.

Simultaneous measurement of cosmology and intrinsic alignments using joint cosmic shear and galaxy number density correlations

“…In particular, adding their subsets to the correlations further decreases ΔFoM below the -only value for the most flexible bias term model. This synergy is presumably related to the internal calibration between the IG and gI signals, as investigated by Zhang (2010). Finally, the full set of shape and number density observables clearly calibrates the nuisance parameters best as it produces the smallest ΔFoM for both the most flexible and the more rigid bias term models.…”

“…The cross-correlations between ellipticity and number density link those signals which depend on both galaxy bias and intrinsic alignments and thus allow for their internal crosscalibration. An example is the study by Zhang (2010) which investigates the interrelations between the IG, gI, and gg terms. In Fig.…”

CFHTLenS tomographic weak lensing cosmological parameter constraints: Mitigating the impact of intrinsic galaxy alignments

“…The model fitting approach does, however, become more promising if the lensing data are analysed simultaneously with galaxy clustering data. These extra data act to self-calibrate the II and GI signals (Zhang 2010;Joachimi & Bridle 2010). Kirk et al (2010) present the first example of such a joint analysis, combining two-dimensional weak lensing data from the 100 square degree lensing survey (Benjamin et al 2007) and SDSS shear-shape clustering data (Mandelbaum et al 2006).…”

Weak lensing power spectra for precision cosmology

“…On the observational side, this requires accurate information on the redshift distribution of source galaxies (Ma et al 2006) and precise measurements of galaxy shapes which correct for observational systematics such as pixelization, noise, blurring by seeing and a spatially variable point spread function (see Massey et al 2007a;Bridle et al 2009). On the theoretical side, astrophysical contaminants, like source lens clustering (Bernardeau et al 1997;Schneider et al 2002), intrinsic alignment (King & Schneider 2003) and the correlation between the gravitational shear and intrinsic ellipticities of galaxies (Hirata & Seljak 2004;King 2005;Joachimi & Schneider 2008;Zhang 2010;Joachimi & Schneider 2009), need to be understood and removed. The prediction of lensing observables also requires precise models of the non-linear matter power spectrum and models for the relation between lensing distortion and large scale matter distribution which go beyond linear theory.…”