Friday.
1601.05417
Quantifying environmental and line-of-sight effects in models of strong gravitational lens systems
McCully, Keeton, Wong, Zabludoff
Matter near a gravitational lens galaxy or projected along the LoS can affect SL observables by more than contemporary measurement errors. Simulate lens fields with realistic 3d mass configurations (self-consistently including kids), and then use lens models to quantify biases and uncertainties associated with different ways of treating the lens environment (ENV) and LoS. Identify the combination of mass, projected offset, and redshift that determines the importance of a perturbing galaxy for lensing. Foreground structures have a stronger effect on the lens potential than background structures, due to non-linear effects in the foreground and downweighting in the background. There is dramatic variation in the net strength of ENV/LoS effects across different lens fields; modeling fields individually yields stronger priors on H0 than ray tracing through N-body simulations. Lens systems in groups tend to have stronger ENV/LoS contributions than non-group lenses. In models, ignoring mass outside the lens yields poor fits and biased results. Adding external shear can account for tidal stretching from galaxies at redshifts z>=z_lens, but it requires corrections for external convergence and cannot reproduce non-linear effects from foreground galaxies. Using the tidal approximation is reasonable for most perturbers as long as non-linear redshift effects are included. Yet even then, the scatter in H0 is limited by the lens profile degeneracy. Asymmetric image configurations produced by highly elliptical lens galaxies are less sensitive to the lens profile degeneracy, so they offer appealing targets for precision lensing analyses in future surveys like LSST.
1601.05720
Constraining multiplicative bias in CFHTLenS weak lensing shear data
Liu, Ortiz-Vazquez, Hill
Several recent cosmo analyses found tension between constraints derived from CFHTLenS data and this derived from other data sets, such as Planck CMB. Similarly, a direct cross-correlation of the CFHTLenS data with Planck CMB lensing data yielded an anomalously low amplitude compared to expectations based on Planck or WMAP-derived cosmo parameters (Liu + Hill 2015). One potential explanation for these results is a multiplicative bias afflicting the CFHTLenS galaxy shape measurements, from which shears are inferred. Simulations are used in the CFHTLenS pipeline to calibrate such biases, but no data-drive constraints have been presented to date. In this paper, cross-correlate CFHTLenS galaxy density maps with CFHTLenS shear maps and Planck CMB lensing maps to independently calibrate the multiplicative shear bias in CFHTLenS, m, following methods suggested by Vallinotto (2012) and Das+2013. Analyze three magnitude-limited galaxy samples, finding 2-4 sigma evidence for m<1 using the deepest sample (i<24), while the others are consistent with m=1 (no bias). This matches the expectation that the shapes of faint galaxies are the most difficult to measure. The results for m are essentially independent of the assumed cosmology, and only weakly sensitive to assumptions about the galaxy bias. Consider 3 galaxy bias models, finding in all cases that the best-fit multiplicative shear bias is less than unity. A value of m~0.9 would suffice to reconcile the amplitude of density fluctuations inferred from CFHTLenS shear 2pt statistics with that inferred from Planck CMB temperature data. This scenario is consistent with the results.
1601.05779
CosmoLike - cosmological likelihood analyses for photometric galaxy surveys
Krause, Eifler
Explore strategies to extract cosmo constraints from joint analysis of cosmic shear, gg lensing, galaxy clustering, cluster number counts and cluster WL. Utilize the CosmoLike software to simulate results from an LSST like data set, specifically, (1) compare individual and joint analyses of the different probes, (2) vary the selection criteria for lens and source galaxies, (3) investigate the impact of blending, (4) investigate the impact of the assumed cosmo model in multi-probe covariances, (6) quantify information content as a function of scales, and (7) explore the impact of intrinsic galaxy alignment in a multi-probe context. The analyses account for all cross correlations within and across probes and include the higher-order (non-Gaussian) terms in the multi-probe covariance matrix. Simultaneously model cosmo parameters and a variety of systematics, e.g., uncertainties arising from shear and photo-z calibration, cluster mass-observable relation, galaxy intrinsic alignment, and galaxy bias (up to 54 parameters altogether). Highlight 2 results: (1) increasing the number density of source galaxies by ~30% which corresponds to solving blending for LSST, only gains little information. (2) Including small scales in clustering and gg lensing, by utilizing HODs, can substantially boost cosmo constraining power. The CosmoLike modules used to compute the results in this paper at github.com/elikrause/CosmoLike_Forecasts.
1601.05786
CFHTLenS revisited: assessing concordance with Planck including astrophysical systematics
Joudaki, Blake, Heymans, Choi, Harnos-Deraps, Hildebrandt, Joachimi, Johnson, Mead, Parkinson, Viola, van Waerbeke
Investigate the impact of astrophysical systematics on cosmic shear cosmo param constraints from CFHTLenS, and the concordance with CMB measurements by Planck. Present updated CFHTLenS cosmic shear tomography measurements extended to degree scales using a covariance calibrated by a new suite of N-body sims. Analyze these measurements with a new model fitting pipeline, accounting for key systematic uncertainties arising from intrinsic galaxy alignments, baryonic effects in the NL matter PS, and photo-z uncertainties. Examine the impact of the systematic degrees of freedom on the cosmo param constraints, both independently and jointly. When the systematic uncertainties are considered independently, the IA amplitude is the only degree of freedom that is substantially preferred by the data. When the sys uncertainties are considered jointly, there is no consistently strong preference in favor of the more complex models. Quantify the level of concordance between the CFHTLenS and Planck datasets by employing two distinct data concordance tests, grounded in Bayesian evidence and information theory. Find that the two data concordance tests largely agree with one another, and that the level of concordance between CFHTLenS and Planck datasets is sensitive to the exact details of the systematic uncertainties included in the analysis, ranging from decisive discordance to substantial concordance as the treatment of the systematic uncertainties becomes more conservative. The least conservative scenario is the one most favored by the cosmic shear data, but it is also the one that shows the greatest degree of discordance with Planck. The data and analysis code are public at github.com/sjoudaki/cfhtlens-revisited.
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