Detection of large-scale intrinsic ellipticity—density correlation from the Sloan Digital Sky Survey and implications for weak lensing surveys

By Rachel Mandelbaum, C. Hirata, M. Ishak, Uros Seljak, J. Brinkmann. 2005

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The power spectrum of weak lensing shear caused by large-scale structure is an emerging tool for precision cosmology, in particular for measuring the effects of dark energy on the growth of structure at low redshift. One potential source of systematic error is intrinsic alignments of ellipticities of neighbouring galaxies [the intrinsic ellipticity-intrinsic ellipticity (II) correlation] that could mimic the correlations due to lensing. A related possibility pointed out by Hirata & Seljak is correlation between the intrinsic ellipticities of galaxies and the density field responsible for gravitational lensing shear [the gravitational shear-intrinsic ellipticity (GI) correlation]. We present constraints on both the II and GI correlations using 265 908 spectroscopic galaxies from the Sloan Digital Sky Survey (SDSS) and using galaxies as tracers of the mass in the case of the GI analysis. The availability of redshifts in the SDSS allows us to select galaxies at small radial separations, which both reduces noise in the intrinsic alignment measurement and suppresses galaxy-galaxy lensing (which otherwise swamps the GI correlation). While we find no detection of the II correlation, our results are none the less statistically consistent with recent detections found using the SuperCOSMOS survey. Extrapolation of these limits to cosmic shear surveys at z ∼ 1 suggests that the II correlation is unlikely to have been a significant source of error for current measurements of σ 8 with ∼ 10 per cent accuracy, but may still be an issue for future surveys with projected statistical errors below the 1 per cent level unless eliminated using photometric redshifts. In contrast, we have a clear detection of GI correlation in galaxies brighter than L. that persists to the largest scales probed (60 h -1 Mpc) and with a sign predicted by theoretical models. This correlation could cause the existing lensing surveys at z ∼ 1 to underestimate the linear amplitude of fluctuations by as much as 20 per cent depending on the source sample used, while for surveys at z ∼ 0.5 the underestimation may reach 30 per cent. The GI contamination is dominated by the brightest galaxies, possibly due to the alignment of brightest cluster galaxies (BCGs) with the cluster ellipticity due to anisotropic infall along filaments, although other sources of contamination cannot be excluded at this point. We propose that cosmic shear surveys should consider rejection of BCGs from their source catalogues as a test for GI contamination. Future high-precision weak lensing surveys must develop methods to search for and remove this contamination if they are to achieve their promise.

Subfields: Astronomy and Astrophysics, Electrical and Electronic Engineering, Instrumentation

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Citations in the corpus

Masses of Galaxy Clusters from Gravitational Lensing (2013, methodology): “This approach has been applied with great success to the SDSS data to measure the ensemble averaged lensing signal around galaxies (e.g., Fischer et al. 2000; Guzik & Seljak 2002; Mandelbaum et al. 2005), groups and clusters (e.g., Mandelbaum et al. 2006; Sheldon et al. 2009).”
Constraints on intrinsic alignment contamination of weak lensing surveys using the MegaZ-LRG sample (2010, methodology): “While the methodology for the analysis of spectroscopic galaxy samples is already well established (Mandelbaum et al. 2006; Hirata et al. 2007), we consider for the first time a sample with only photometric redshift information, obtained fromthe MegaZ-LRG catalogue.”
Galaxy Alignments: Observations and Impact on Cosmology (2015, methodology): “8 p , from the WiggleZ data of Mandelbaum et al. (2011). Results are shown averaged over all WiggleZ regions, for the two redshift subsamples.”
Cosmological constraints from the 100-deg2 weak-lensing survey (2007, methodology): “With the exception of u∗ these filters are designed to match the Sloan Digital Sky Survey (SDSS) photometric system (Fukugita et al. 1996).”
Gravitational lensing (2010, background): “They quantified this systematic effect [191, 298] and showed that it can substantially reduce the measured shear signal, leading to a likely underestimate of the σ8 parameter by several per cents.”
Intrinsic alignments of SDSS-III BOSS LOWZ sample galaxies (2014, background): “…function of mass. Observationally, several studies have detected the intrinsic alignments for Luminous Red Galaxies (LRGs) to tens of Mpc scales (Mandelbaum et al. 2006; Hirata et al. 2007; Okumura, Jing & Li 2009; Joachimi et al. 2011), finding the radial dependence of the signal to be…”
CFHTLenS tomographic weak lensing cosmological parameter constraints: Mitigating the impact of intrinsic galaxy alignments (2013, methodology): “This modification to the original model was motivated by comparisons of the model predictions to measurements of intrinsic alignments from data (Mandelbaum et al. 2006), and simulations (Heymans et al. 2004), and the desire to make the linear tidal field alignment model more realistic on small…”
KiDS+GAMA : cosmology constraints from a joint analysis of cosmic shear, galaxy-galaxy lensing, and angular clustering (2017, background): “…although intrinsic alignments have been detected for luminous red galaxies (e.g. Joachimi et al. 2011; Singh, Mandelbaum & More 2015), the constraints for less luminous red galaxies and blue galaxies are consistent with zero (Mandelbaum et al. 2006; Hirata et al. 2007; Mandelbaum et al. 2011).”
The Intrinsic Alignment of Galaxies and its Impact on Weak Gravitational Lensing in an Era of Precision Cosmology (2014, methodology): “(90), Mandelbaum et al. (2006b) defined for the galaxy-intrinsic shear correlation function the estimator ξ̂g+(rp,Π) = S+(D −R) RR = S+D − S+R RR , (91) where S+D is the sum over all pairs with separations rp and Π of the + component of shear, i.e.”
Simultaneous measurement of cosmology and intrinsic alignments using joint cosmic shear and galaxy number density correlations (2009, methodology): “…because it is known that both the intrinsic alignments ad the galaxy bias vary considerably with galaxy type and luminosity (for recent examples see Mandelbaum et al. 2006; Hirata et al. 2007; McCracken et al. 2008; Swanson et al. 2008; Simon et al. 2009; Cresswell & Percival 2009; Wang et al.…”
Spin alignments within the cosmic web: a theory of constrained tidal torques near filaments (2015, background): “…and observational (e.g. Brown et al. 2002; Lee & Pen 2002; Bernstein & Norberg 2002; Heymans et al. 2004; Hirata et al. 2004; Hirata & Seljak 2004; Mandelbaum et al. 2006; Hirata et al. 2007; Mandelbaum et al. 2011; Joachimi et al. 2011, 2013a) efforts have been invested to control the level of…”
COSMOLIKE - cosmological likelihood analyses for photometric galaxy surveys (2016, methodology): “…we consider intrinsic alignment of source galaxies, which has been studied in observations, simulations and theory (e.g. Hirata & Seljak 2004; Mandelbaum et al. 2006; Joachimi & Bridle 2010; Singh, Mandelbaum & More 2014; Troxel & Ishak 2014; Tenneti et al. 2015; Blazek, Vlah & Seljak 2015).”
Density profiles of galaxy groups and clusters from SDSS galaxy–galaxy weak lensing (2006, background): “Correlations between intrinsic ellipticity and density have been demonstrated robustly using bright, red galaxies on large scales (Mandelbaum et al. 2006) and on small scales (Mandelbaum et al. 2005c; Donoso et al. 2006; Yang et al. 2006), with the effect being more controversial for the gen- c©…”
Evidence of the accelerated expansion of the Universe from weak lensing tomography with COSMOS (2009, background): “This reduces potential contamination, given that LRGs were found to carry the strongest alignment signal (Mandelbaum et al. 2006, 2009; Hirata et al. 2007).”
The WiggleZ Dark Energy Survey: Direct constraints on blue galaxy intrinsic alignments at intermediate redshifts (2009, methodology): “First, Mandelbaum et al. (2006b) presented GI and II correlations for SDSS Main spectroscopic sample galaxies (typical z ∼ 0.1) split into luminosity bins, which included a positive detection of GI signal for the bins with L > L∗.”
Observational probes of cosmic acceleration (2012, background): “Also, intrinsic alignments of galaxies were detected at high significance even in the linear regime, at a level that represented a potentially serious systematic error even for then-ongoing surveys (Mandelbaum et al., 2006).”