The impact of the observed baryon distribution in haloes on the total matter power spectrum

Abstract

The interpretation of upcoming weak gravitational lensing surveys depends critically on our understanding of the matter power spectrum on scales k < 10 h Mpc −1 , where baryonic processes are important. In this paper we study the impact of gas flows associated with galaxy formation on the matter power spectrum using a halo model that treats the stars and gas separately from the dark matter distribution. The baryonic components are constrained empirically: the hot gas using fits to X-ray observations of groups and clusters of galaxies, and the stellar component using a halo occupation distribution. Since X-ray observations cannot generally measure the hot gas content outside r 500c , we vary the gas density profiles beyond this radius. Compared with dark matter only models, we find a total power suppression of 1 % (5 %) on scales 0.2 − 1 h Mpc −1 (0.5 − 2 h Mpc −1 ), where lower baryon fractions result in stronger suppression. We show that groups of galaxies (10 13 < m 500c /(h −1 M ) < 10 14 ) dominate the total power at all scales k 10 h Mpc −1 . We illustrate the importance of measuring accurate halo masses by comparing models that do and do not account for a hydrostatic bias of 1−b = 0.7 in the halo masses from X-ray observations. We find that using biased halo masses results in an underestimation of the power suppression of up to 4 % at k = 1 h Mpc −1 . Contrary to work based on hydrodynamical simulations, our conclusion that baryonic effects can no longer be neglected is not subject to uncertainties associated with our poor understanding of feedback processes. Our findings highlight the need for observations to probe the outskirts of groups and clusters since these observations are the most constraining for the power suppression on scales k 1 h Mpc −1 .

The BAHAMAS project: effects of dynamical dark energy on large-scale structure

“…In addition, it is well known that baryonic effects on the matter power spectrum are of the order of ∼10-20% and cause a suppression in the power spectrum at k > ∼ 0.1 Mpc −1 h (van Daalen et al 2011;Mummery et al 2017;Schneider et al 2019;van Daalen et al 2020;Debackere et al 2020). The DDE cosmologies considered here produce effects of similar magnitude, although they extend throughout the linear and non-linear regime and should therefore be distinguishable from baryonic effects given a wide enough range of well-sampled k values.…”

“…It is therefore vital for the calibration statistics to be mostly unaffected by a change in cosmology, or to re-calibrate after every change. The calibration statistics for BAHAMAS are the observed stellar and hot gas mass of haloes, which were specifically chosen because they are expected to be relatively insensitive to changes in cosmology (as confirmed in McCarthy et al 2018, S20, and later here) and because these quantities are directly related to impact of baryons on the matter power spectrum (van Daalen et al 2020;Debackere et al 2020).…”

Euclid: Impact of non-linear and baryonic feedback prescriptions on cosmological parameter estimation from weak lensing cosmic shear

“…On the small scales of interest, however, baryons collapse into the dark matter haloes to form stars, or are heated up, or even expelled into the intergalactic medium. These processes modify the matter distribution, and it is therefore important to account for baryonic physics when computing the matter power spectrum P δδ (k, z) (e.g., Casarini et al 2012;Castro et al 2018;Debackere et al 2020). This can be done by multiplying the non-linear power spectrum, P δδ (k, z) -computed using one of the non-linear prescriptions discussed above -with B(k, z), a 'baryon correction model' (BCM) that captures the baryonic effects (e.g., Semboloni et al 2011), so that…”

“…Moreover, our ability to extract cosmological information from WL measurements on small scales is limited further by baryonic feedback processes (Semboloni et al 2011) because gas cooling, star formation, galactic winds, supernova explosions, and feedback from active galactic nuclei (AGNs) modify the expected distribution of matter on small scales (Jing et al 2006;Rudd et al 2008;Casarini et al 2011bCasarini et al , 2012Castro et al 2018;Debackere et al 2020). Accurate predictions of the matter power spectrum on those scales require hydrodynamical simulations that not only need to reproduce the non-linear clustering of cold dark matter particles, but should also reliably describe the baryonic component.…”

Cross-correlation of the astrophysical gravitational-wave background with galaxy clustering

“…Note in particular that the magnitude of the signal changes drastically with k max , meaning that the autocorrelation signal depends heavily on the shape of the low redshift power spectrum on nonlinear scales. This is likely one of the causes behind the discrepancy between Jenkins et al and Cusin et al and suggests that an accurate prediction of the autocorrelation signal should take into account not only the shot-noise contribution [38,44], but also the uncertainties due to baryonic effects in the matter distribution at small scales [50,51]. We point out, in particular, that the galaxy catalogue based on dark-matteronly simulations of [52] and the HaloFit model of [53] are not designed to consistently or accurately model this uncertainty.…”