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

Abstract

We present a finely-binned tomographic weak lensing analysis of the Canada-FranceHawaii Telescope Lensing Survey, CFHTLenS, mitigating contamination to the signal from the presence of intrinsic galaxy alignments via the simultaneous fit of a cosmological model and an intrinsic alignment model. CFHTLenS spans 154 square degrees in five optical bands, with accurate shear and photometric redshifts for a galaxy sample with a median redshift of z m = 0.70. We estimate the 21 sets of cosmic shear correlation functions associated with six redshift bins, each spanning the angular range of 1.5 < θ < 35 arcmin. We combine this CFHTLenS data with auxiliary cosmological probes: the cosmic microwave background with data from WMAP7, baryon acoustic oscillations with data from BOSS, and a prior on the Hubble constant from the HST distance ladder. This leads to constraints on the normalisation of the matter power spectrum σ 8 = 0.799 ± 0.015 and the matter density parameter Ω m = 0.271 ± 0.010 for a flat ΛCDM cosmology. For a flat wCDM cosmology we constrain the dark energy equation of state parameter w = −1.02 ± 0.09. We also provide constraints for curved ΛCDM and wCDM cosmologies. We find the intrinsic alignment contamination to be galaxy-type dependent with a significant intrinsic alignment signal found for early-type galaxies, in contrast to the late-type galaxy sample for which the intrinsic alignment signal is found to be consistent with zero.

Cosmic discordance: are Planck CMB and CFHTLenS weak lensing measurements out of tune?

“…Kilbinger et al (2013) performed a 2d cosmic shear analysis of the CFHTLenS data, producing constraints on the ΛCDM model which they approximated by σ8(Ωm/0.27) 0.59 = 0.787 ± 0.032. Heymans et al (2013) (HE13 henceforth) performed a tomographic cosmic shear analysis of the CFHTLenS data, dividing the galaxies into six tomographic redshift bins (with photometric redshift estimate between 0.2 and 1.3) and taking into account the effect of galaxy intrinsic alignments using a free parameter for the overall intrinsic alignment amplitude. For each tomographic bin combination, they measured the real space shear-shear correlation functions ξ+,−(θ) in 5 evenly logspaced angular bins for 1 θ 40 arcmin.…”

“…The Planck Collaboration et al (2013d) noted an approximately 2σ discrepancy between their Planck CMB analysis and the CFHTLenS analysis of Heymans et al (2013) and noted that further work will be required to resolve the difference. They allow freedom in the effect of lensing on the primary anisotropies and find that a larger lensing amplitude is preferred when the Planck data is combined with smaller scale CMB measurements.…”

“…In contrast to the earlier papers, we use the full 6 tomographic redshift bins and marginalise over intrinsic alignments, as in Heymans et al (2013) and described in Section 2. Earlier papers drew conclusions about agreement between datasets by comparing marginalised contours in one or two dimensions.…”

“…We perform an independent analysis of the CFHTLenS six bin tomography results of Heymans et al (2013). We extend their systematics treatment and find the cosmological constraints to be relatively robust to the choice of non-linear modeling, extension to the intrinsic alignment model and inclusion of baryons.…”

The potential of likelihood-free inference of cosmological parameters with weak lensing data

“…One such setting would be that of tomographic weak lensing analysis, as in Heymans et al (2013), wherein the data vector consists of auto-and cross-correlation functionsξ i,j ± within or between various bins in redshift. In this setting, where the dimension of the data vector is inherently much larger, the motivation for principled dimension reduction is apparent.…”