Weak lensing probes of primordial non-Gaussianity and mass estimators of weak-lensing clusters
Zusammenfassung der Projektergebnisse
The research programme made possible by this funding followed three different topics: shear-peak cosmology, galaxy-galaxy lensing, and optimal estimation of the matter power spectrum using measurements of the cluster power spectrum. The first topic was the cosmological information of weak lensing (WL) peaks, focusing on two other statistics besides their abundance: the stacked tangential-shear profiles and the peak-peak correlation function. We used a large ensemble of simulated WL maps with survey specifications relevant to future missions like Euclid and lsst, to measure and examine the three peak probes. We found that the auto-correlation function of peaks with high signal-to-noise (S{N ) ratio measured from fields of size 144 deg2 had a maximum of ~ 0.3 at an angular scale ϑ ~ 10 arcmin. For peaks with smaller S{N , the amplitude of the correlation function decreased, and its maximum occurred on smaller angular scales. The stacked tangential-shear profiles of the peaks also increased with their S{N . We compared the peak observables measured with and without shape noise and found that for S{N ~ 3, only ~ 5% of the peaks were due to large-scale structures, the rest being generated by shape noise. The correlation function of these small peaks was therefore very weak compared to that of small peaks measured from noise-free maps, and also their mean tangential-shear profile was a factor of a few smaller than the noisefree one. The covariance matrix of the probes was also examined: the correlation function was only weakly covariant on scales ϑ < 30 arcmin, and slightly more on larger scales; the shear profiles were very correlated for ϑ > 2 arcmin. The cross-covariance of the three probes was relatively weak. Using the Fisher-matrix formalism, we computed the cosmological constraints for {Ωm, σ8, w, ns} considering each probe separately, as well as in combination. We found that the peak-peak correlation and shear profiles yield marginalized errors which were larger by a factor of 2-4 for {Ωm, σ8} than the errors yielded by the peak abundance alone, while the errors for {w, ns} were similar. By combining the three probes, the marginalized constraints were tightened by a factor of ~ 2 compared to the peak abundance alone, the least contributor to the error reduction being the correlation function. This work therefore recommends that future WL surveys use shear peaks beyond their abundance in order to constrain the cosmological model. The second topic was to investigate the potential of galaxy-galaxy lensing and galaxy clustering data to simultaneously constrain both the cosmological and galaxy formation models. We performed a comprehensive exploration of these signals and their covariances through a combination of analytic and numerical approaches. First, we derived analytic expressions for the projected galaxy correlation function and stacked tangential shear profile and their respective covariances, which included Gaussian and discreteness noise terms. Secondly, we measured these quantities from mock galaxy catalogues obtained from the Millennium-XXL simulation and state-of-the-art semi-analytic models of galaxy formation. We found that on large scales (R > 10 h´1 Mpc), the galaxy bias was roughly linear and deterministic. On smaller scales (R ≤ 5 h´1 Mpc) the bias was a complicated function of scale and luminosity, determined by the different spatial distribution and abundance of satellite galaxies present when different magnitude cuts are applied, as well as by the mass dependence of the host haloes on magnitude. Our theoretical model for the covariances provided a reasonably good description of the measured ones on small and large scales. However, on intermediate scales (1 < R < 10 h´1 Mpc), the predicted errors were ~ 2–3 times smaller, suggesting that the inclusion of higher-order, non-Gaussian terms in the covariance will be required for further improvements. Importantly, both our theoretical and numerical methods showed that the galaxy-galaxy lensing and clustering signals have a non-zero cross-covariance matrix with significant bin-to-bin correlations. Future surveys aiming to combine these probes must take this into account in order to obtain unbiased and realistic constraints. The third topic was on the power spectrum of galaxy clusters as a probe of the cosmological model. We developed a formalism to compute the optimal weights for the estimation of the matter power spectrum from cluster power spectrum measurements. We found a closed-form analytic expression for the optimal weights, which takes into account: the cluster mass, finite survey volume effects, survey masking, and a flux limit. The optimal weights were determined. We compared our optimal weighting scheme with mass weighting and also with the original power spectrum scheme of Feldman, Kaiser and Peacock (1994). We showed that the optimal weighting scheme outperforms these approaches for both volume- and flux-limited cluster surveys. Finally, we presented a new expression for the Fisher information matrix for cluster power spectrum analysis. Our expression showed that for an optimally-weighted cluster survey the cosmological information content is boosted, relative to the standard approach of Tegmark et al. (1997).
Projektbezogene Publikationen (Auswahl)
- The cosmological information of shear peaks: beyond the abundance. MNRAS 432, 1338 (2013)
L. Marian, R. E. Smith, S. Hilbert,P. Schneider
(Siehe online unter https://doi.org/10.1093/mnras/stt552) - Precision cosmology in muddy waters: Cosmological constraints and N-body codes. MNRAS 440, 249 (2014)
R. E. Smith, D. S. Reed, D. Potter, L. Marian, M. Crocce, B. Moore
(Siehe online unter https://doi.org/10.1093/mnras/stu272) - Toward optimal cluster power spectrum analysis
R. E. Smith, L. Marian
- An exploration of galaxy-galaxy lensing and galaxy clustering in the Millennium-XXL simulation. MNRAS (2015)
L. Marian, R. E. Smith, R. Angulo
