Quantifying the effect of baryon physics on weak lensing tomography

Abstract

We use matter power spectra from cosmological hydrodynamic simulations to quantify the effect of baryon physics on the weak gravitational lensing shear signal. The simulations consider a number of processes, such as radiative cooling, star formation, supernovae and feedback from active galactic nuclei (AGN). Van Daalen et al. (2011) used the same simulations to show that baryon physics, in particular the strong feedback that is required to solve the overcooling problem, modifies the matter power spectrum on scales relevant for cosmological weak lensing studies. As a result, the use of power spectra from dark matter simulations can lead to significant biases in the inferred cosmological parameters. We show that the typical biases are much larger than the precision with which future missions aim to constrain the dark energy equation of state, w_0. For instance, the simulation with AGN feedback, which reproduces X-ray and optical properties of groups of galaxies, gives rise to a ~40% bias in w_0. We demonstrate that the modification of the power spectrum is dominated by groups and clusters of galaxies, the effect of which can be modelled. We consider an approach based on the popular halo model and show that simple modifications can capture the main features of baryonic feedback. Despite its simplicity, we find that our model, when calibrated on the simulations, is able to reduce the bias in w_0 to a level comparable to the size of the statistical uncertainties for a Euclid-like mission. While observations of the gas and stellar fractions as a function of halo mass can be used to calibrate the model, hydrodynamic simulations will likely still be needed to extend the observed scaling relations down to halo masses of 10 ^12 M_sun/h.Comment: 17 pages, 14 Figures, MNRAS accepted. Small changes to the published version: typos in Eq. 4 corrected, Figure 2 updated (y-ticks of the previous version were wrong). Bibliography updated with published papers when possibl

Probing cosmology with weak lensing Minkowski functionals

“…[75] have shown recently with hydrodynamic simulations including processes like radiative cooling, star formation, supernovae and feedback from active galactic nuclei that baryon physics, in particular the strong feedback required to solve the overcooling problem, modifies the matter power spectrum on scales relevant for cosmological lensing studies. In [76] they show that the use of power spectra from pure CDM simulations can lead to significant biases in the cosmological parameters inferred from the weak lensing shear signal. Figure 6 for zs = 2 and θG = 1 arcmin, but showing only the constraints from the MFs combined (pink) and the convergence power spectrum (turquoise).…”

Observational probes of cosmic acceleration

“…In their simulations, AGN feedback has the effect of reducing the baryon content of the haloes, consistent with X-ray observations of intrahalo gas: the matter power suppression quoted above is thus within the range of "reasonable" rather than "extreme/unrealistic" models. Semboloni et al (2011) show that the results of the simulations can be captured by a parameterized halo model for the baryons, so one may be able to use this approach to marginalize over uncertainties, but at the price of reducing the cosmological information derived from WL measurements on these scales. Moreover, their mitigation procedure involves tuning the halo model to the van Daalen et al (2011) simulations.…”

“…Moreover, their mitigation procedure involves tuning the halo model to the van Daalen et al (2011) simulations. Therefore one should worry that the removal of baryonic physics-induced bias seen by Semboloni et al (2011) might not be realized in practice, if the simulation captures the qualitative features of AGN feedback but does not quantitatively reproduce the correct functional form. Zentner et al (2012) avoid this issue by fitting cosmic shear power spectra based on the van simulations using a mitigation procedure tuned to the Rudd et al (2008) simulations.…”

Luminosity Bias: From Haloes to Galaxies

“…One advantage of gas simulations over semi-analytics is that they can follow the redistribution of matter due to outflows of baryons. Calculations using the OverWhelmingly Large Simulations have shown that the physics of galaxy formation, particularly active galactic nucleus (AGN) feedback, has an impact on the distribution of matter which has implications for the interpretation of weak lensing measurements (Semboloni et al 2011;van Daalen et al 2011).…”