Tomographic weak-lensing shear spectra from largeN-body and hydrodynamical simulations

Abstract

Context. Forthcoming experiments will enable us to determine tomographic shear spectra at a high precision level. Most predictions about them have until now been based on algorithms yielding the expected linear and non-linear spectrum of density fluctuations. Even when simulations have been used, so-called Halofit predictions on fairly large scales have been needed. Aims. We wish to go beyond this limitation. Methods. We perform N-body and hydrodynamical simulations within a sufficiently large cosmological volume to allow a direct connection between simulations and linear spectra. While covering large length-scales, the simulation resolution is good enough to allow us to explore the high-harmonics of the cosmic shear (up to ∼ 50 000), well into the domain where baryon physics becomes important. We then compare shear spectra in the absence and in presence of various kinds of baryon physics, such as radiative cooling, star formation, and supernova feedback in the form of galactic winds. Results. We distinguish several typical properties of matter fluctuation spectra in the different simulations and test their impact on shear spectra. Conclusions. We compare our outputs with those obtainable using approximate expressions for non-linear spectra, and identify substantial discrepancies even between our results and those of purely N-body results. Our simulations and the treatment of their outputs however enable us, for the first time, to obtain shear results that are fully independent of any approximate expression, also in the high-range, where we need to incorporate a non-linear power spectrum of density perturbations and the effects of baryon physics. This will allow us to fully exploit the cosmological information contained in future high-sensitivity cosmic shear surveys, exploring the physics of cosmic shears via weak lensing measurements.

The effects of baryons on the halo mass function

“…Pedrosa, Tissera & Scannapieco 2009; Duffy et al 2010; Tissera et al 2010). In line with this result on halo concentration, also the total matter power spectrum in radiative hydrodynamic simulations has been shown to have a higher amplitude than for DM‐only N ‐body simulations, small non‐linear scales k > 1 h Mpc −1 (Jing et al 2006; Rudd et al 2008; van Daalen et al 2011; Casarini et al 2012). However, also the simple case of non‐radiative hydrodynamics has been suggested to increase halo concentration, as a consequence of a redistribution of energy between baryons and DM during halo collapse (Rasia, Tormen & Moscardini 2004; Lin et al 2006).…”

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

“…Jing et al (2006), Rudd et al (2008), Guillet et al (2010), Casarini et al (2012) all confirmed the significance of baryonic feedback at k > 1h Mpc −1 by comparing hydrodynamical simulations to pure N-body dark matter ones. Schaye et al (2010) .…”

Fourier band-power E/B-mode estimators for cosmic shear

“…Notice that in real-space, these estimators are very efficient at excluding small-scale modes in the shear correlation functions. Thus these estimators can be used to help render cosmic shear measurements insensitive to potential systematic effects on small scales, like baryonic effects in the matter power spectrum (e.g., Zhan & Knox 2004;White 2004;Rudd et al 2008;van Daalen et al 2011;Casarini et al 2012) or the small-scale selection effects in shear measurements (e.g., Hartlap et al 2011). Similarly, these estimators do not use the shear correlation functions at zero separation, rendering them unbiased by shape noise.…”